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SS2 Chemistry Lesson Note (Second Term) 2023
SECOND TERM E-LEARNING NOTES
SUBJECT: CHEMISTRY CLASS: SS 2
SCHEME OF WORK
- Revision of last term’s work
- Hydrogen: Configuration, possible oxidation, Isotopes of hydrogen and unique Position of hydrogen in the periodic table, Laboratory and Industrial preparation of hydrogen, Physical and Chemical Properties, compounds of hydrogen, Uses and Test of Hydrogen.
- Oxygen: Laboratory and industrial preparation of oxygen, general properties of
oxygen- Physical and chemical properties of oxygen, Oxides of oxygen, Uses and
Test of oxygen
- Halogens: 1. Electronic Configuration of Halogens, Physical Properties of Halogens
and Gradation down the Group, Chemical properties of halogens and Gradation
down the group, Uses of halogens and their compounds.
- Halogens: Preparation of chlorine (Laboratory and Industrial), Properties of chlorine
(Physical and chemical), Hydrogen chloride gas: Laboratory preparation, Properties
and uses, Test for HCl gas and Fountain experiment.
- Nitrogen: General properties of Nitrogen–group VA elements, Laboratory and
Industrial preparation of Nitrogen, Properties and Uses of Nitrogen, Compound of nitrogen – Ammonia- Laboratory and Industrial Preparation, Properties and Uses, Test for Ammonia, Fountain experiment
- Mid-Term Break and Holiday ASSIGNMENT
- Nitrogen: Compounds of Nitrogen: Trioxonitrate(V) acid – Laboratory Preparation,
Properties and Uses, Trioxonitrate(V) salts- Action of heat, Test for trioxonitrate(V)
- Sulphur: General Properties of Group VIA Element, Allotropes and uses of sulphur,
Compounds of sulphur- Trioxosulphate(IV) acids and its salts, Tetraoxosulphate(VI)
acid: Industrial preparation, Reactions and uses.
WEEK 1: Revision of last term’s work.
- Configuration, possible oxidation, Isotopes of hydrogen and unique Position of hydrogen of hydrogen in periodic table,
- Laboratory and Industrial preparation of hydrogen
- Physical and chemical properties,
- Compounds of hydrogen, Uses and test of hydrogen.
PERIOD 1: CONFIGURATION, POSSIBLE OXIDATION AND ISOTOPES OF HYDROGEN AND UNIQUE POSITION OF HYDROGEN OF HYDROGEN IN PERIODIC TABLE.
Hydrogen is the first element in the periodic table with nucleus and electron. It is a gas; diatomic molecule in which two atoms of hydrogen are covalently bonded. The atomic number of hydrogen is one. The electronic configuration of hydrogen is 1s1. It has oxidation number of +1 and -1
ISOTOPES OF HYDROGEN
Hydrogen exhibits Isotope with Hydrogen or protium [11H], Deuterium or heavy hydrogen [21H or D] and tritium [31H or T] as the Isotopes. These Isotopes have relative atomic masses of 1, 2 and 3 respectively.
The Isotopes have similar chemical properties but different physical properties although tritium is radioactive.
UNIQUE POSITION OF HYDROGEN IN THE PERIODIC TABLE
It can lose this single electron to form positive ions[H+] just like the elements in groups [Li, Na, K, Rb, Cs and Fr] and based on the argument it can be considered to be placed in group 1 along with group 1 elements. However, the H+ ion is not stable like ions formed by group 1 elements. Most of the properties of H+ are not similar to the properties of group I elements.
Hydrogen can also gain one electron to form hydride ion (H–) similar to halogens (group 7 elements) forming halides ion. Thus hydrogen is unique and anomalous in being similar to two different groups of elements. With electro positive alkali and alkali-earth metals, hydrogen forms compounds like LiH, NaH, and CaH2 etc. Similar to halogens form LiCl, Na, CaCl2 etc. On being electrolysed these hydrides yield hydrogen or halogen at the anode showing the similarities between the two. The ionisation energy of hydrogen and halogen are comparable. While those of alkali- metal are very low. It is similar to halogen in been a non-metal, a bad conductor of heat and electricity and diatomic. Hydrogen form covalent compound like those of halogens.
- To which group does hydrogen belong?
- What is the position of hydrogen in the periodic table?
- Mention the existing Isotopes of hydrogen
- Discuss the uniqueness of hydrogen
PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF HYDROGEN.
Laboratory preparation of hydrogen:
Hydrogen is liberated when active metals react with dilute mineral acid, water or steam.e.g action of zinc on H2SO4
Zn(s) + H2SO4(aq) ZnSO4 (aq) +H2 (g)
The hydrogen gas is dried by passing it through Calcium chloride. The apparatus is set up as shown below.
Dilute hydrochloric acid can also be used in place of H2SO4. Magnesium and iron can be used in the place of zinc.
Zn(s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)
Mg(s) + H2SO4 (aq) MgSO4(aq) + H2 (g)
Dilute trioxonitrates (v) acid is never used in the preparation of hydrogen because of its strong oxidizing property and it produces water instead of hydrogen on reaction with metals. However, very dilute trioxonitates (v) acid give out hydrogen on reaction with Magnesium.
Hydrogen can also be prepared in the laboratory in the following ways,
- By the action of Sodium hydroxide on zinc metal or aluminium.
Zn(s) + 2NaOH(aq) Na2ZnO2(s) + H2(g)
2Al(s) + 2NaOH(aq) + 2H2O(l) 2NaAlO2(s) + 3H2 (g)
- Action of steam on heated metals e.g. Iron, Magnesium.
3Fe(s) + 4H2O(g) → 2NaOH(aq) + H2(g)
PREPARATION OF DRY HYDROGEN
The hydrogen gas produced in the first method of flask containing concentrated tetraoxosulphate (vi) acid or anhydrous calcium (ii) chloride as d drying agents.
SUB TOPIC 2: INDUSRIAL PREPARATION OF HYDROGEN
Hydrogen can be prepared industrially by different methods. These methods are as follows;
From water gas; in this case, water gas and excess stream are passed over a catalyst such as Iron (III) oxide, Fe2O3 at a temperature of 723k. The products are hydrogen and carbon (iv) oxide as shown in the equation below.
CO(g) + H2 (g) + H2O ⇌ CO2 (g) +2H2 (g)
It is a reversible reaction. CO2 is dissolved in water under pressure of 30atm or absorbed by caustic soda, leaving hydrogen in good yield. This is Bosch process.
H2O(l) + CO2( g) H2CO3(aq)
From natural gas. E.g methane – when natural gas is heated to a temperature of 1000 [thermal cracking] hydrogen is produced as shown in the equation below
CH4(g) 2H2(g) + C(s)
Methane [CH4] is one of the main constituents of natural gas.
METHOS 3 – FROM HYDROCARBONS
When hydrocarbon e.g methane or propane mixed with steam it is heated to a temperature of 800 in the presence of nickel catalysts, CO(g) and H2(g) are produced.
CH4(g) + H2O(g) CO(g) + 3H2(g)
The mixture of carbon (ii) oxide and hydrogen gas is called synthestic gas. The mixture of [CO(g) + H2(g) is reacted with more steam
CO(g) + H2(g) + H2O(g) ⇋ CO2(g) + 2H2(g)
The CO2(g) is removed by absorption in water or any alkali such as Sodium hydroxide [NaOH] solution.
METHOD 4 – FROM COAL
Here, steam is passed over red-hot coal to obtain water gas[CO + H2]:
C(s) + H2O(g) CO(g) + H2(g)
The water gas [CO + H2] is reacted with more steam in the presence of nickel or platinum catalyst to produce CO(g) + H2(g) + H2O(g) ⇋ CO2(g) + 2H2(g)
METHOD 5- FROM ELECTROLYSIS OF BRINE
Hydrogen is obtained as a by- production in the electrolysis of brine for the large scale production of Sodium hydroxide and Chlorine H2 can also be produced by electrolysis of acidified water
- What do you observe when a piece of sodium is placed on the surface of water?
- With equations only, describe at least two more methods of laboratory preparation of hydrogen.
- What the precaution that one must take while preparing Hydrogen.
- With equations only describe the preparation of hydrogen from hydrocarbons.
PERIOD 3; PHYSICAL AND CHEMICAL PROPERTIES OF HYDROGEN
- It is a colourless, odourless and tasteless gas which burns in air with a high pitch sound.
- It is combustible and when it burns in the absence of gas, it burns quietly with pale blue flame.
- It is the highest known gas.
- It is 14.4 times less than air.
- It exists ad diatomic molecule [H2 ]
- At high pressure, hydrogen can be liquefy at a critical temperature of -235
- It is neutral to litmus and is insoluble in water
- It does not support combustion.
The chemical reactions of hydrogen arise from the fact that it can donate its single electron to form a positive ion [H+]; it can accept electron [to give a dublet structure] to form a negative hydride ion [H–] and it can share electron with another atom to form a covalent molecule.
- Hydrides of hydrogen: An important reaction of hydrogen is the formation of hydride with metals and non-metals.
- Metallic hydrides: Hydrogen is slightly electro negative and forms ionic hydrides e.g. NaH (Na++ H-) with alkali metals which are strongly electro positive. These hydrides contain the hydride ion H–
2Li + H2 → 2LiH (Lithium hydride)
Ca + H2 CaH2[ Calcium hydride]
The hydrides react with water with the liberation of hydrogen.
CaH2(s) + 2H2O(l) Ca[OH]2(aq) + 2H2(g)
(ii) Non-metallic hydrides: Hydrogen forms mainly covalent compounds with less electropositive metals [e.g. aluminium] and with non-metals. These are covalent hydrides. The reaction is spontaneous as shown in the reaction with fluorine and chlorine.
F2(g) + H2(g) 2HF ——————-(1)
Cl2(g) + H2(g) 2HCl (g) —————–(2)
The reaction with chlorine is explosive in the presence of sunlight. Reactions with oxygen, sulphur and nitrogen require the use of catalyst.
Hydrogen reacts with molten sulphur to form hydrogen sulphide which smells like a rotten egg and it also reacts with nitrogen to form ammonia.
H2(g) + S(s) H2S(g) ————(3)
3H2(g) + N2(g) 2NH3(g)———(4)
- Hydrogen is strong reducing agent when it is passed over the heated oxides as shown below.
PbO(s) + H2(g) Pb(s) + H2O(g)
FeO4(s) + 4H2(g) ⇌ 3Fe(s) + 4H2O(g)
The reaction of tri-iron tetraoxide and hydrogen is a reversible reaction, other reduction reaction are
- CuO(s)+ H2(g) Cu(s) + H2O(g)
- ZnO(s)+ H2(g) Zn(s) + H2O(g)
- Fe2O3+ 3H2(g) 2Fe(s) + 3H2O(g)
- Hydrogen burns in air with pop sound and with formation of water [steam] as shown in the equation below.
2H2(g) + O2(g) 2H2O(g)
The reaction is explosive and gives out a large amount heat.
- List three physical properties of hydrogen with equations where necessary.
- With equations only represent the reaction of hydrogen with (i) non-metals (ii) metals.
PERIOD 4 : USES OF HYDROGEN AND COMPOUNDS OF HYDROGEN
- It is used in the synthesis of ammonia as shown in the equation below
N2(g) + 3H2(g) ⇌ 2NH3(g)
The ammonia formed is used in the manufacture of fertilizers, drugs, plastics, wares, dyes among others.
- It is used in the hardening of vegetable and animal oils for the manufacture of Margarine, candles, soap among others. The hydrogenation reaction occurs at high pressure and in presence of catalyst.
- It is used to inflate airships and balloons, but hydrogen is very flammable. The use of hydrogen in balloons, but hydrogen in very flammable. The use of hydrogen in balloons is due to its low density.
- In oxy-hydrogen flames, small quantities of hydrogen are required to produce high temperature that can melt metals.
- It is used in the synthesis of methanol and HCl(aq)
- Hydrogen + powder coal + oil at high pressure and temperature when a mixture of hydrocarbon is called synthetic petroleum from petrol (gasoline) and lubricants are obtained.
- Gaseous hydrogen is a constituent of coal gas and water gas, and liquid hydrogen is used as rocket fuel.
COMPOUNDS OF HYDROGEN
When hydrogen combines with other elements it forms hydrides
- The hydrides of alkali and alkaline earth metals are crystalline solids with high melting points that conduct electricity when molten. They react with water to liberate hydrogen gas.
CaH2 + 2H2O Ca(OH)2 + 2H2
- Boron and aluminium form complex covalent hydrides which are important reducing agents especially in organic chemistry. Some of them are lithium tetrahydridoaluminate (iii) and sodium tetrahydridoborate (iii)
TEST FOR HYDROGEN
If a lighted splint is plunged into a gas jar of hydrogen, it gives a pop sound.
- Enumerate five uses of hydrogen.
- How can you test the presence of hydrogen in the laboratory?
- If the valency of hydrogen is one and that of oxygen is two the formula is ___________. (a) HO2(b) H2O (c) 2OH (d) H2O3
- One of the Isotopes of hydrogen is _____________. (a) Ozone (b) Deuterium (c) diamond (d) graphite
- Hydrogen is prepared in the laboratory by the action of dilute H2SO4on the following metals except (a) Zn (b) Na (c)Al (d)Fe
- The gas given out when sodium reacts with water is ……….. (a) oxygen (b) hydrogen (c) nitrogen (d) Chlorine
- On a large scale hydrogen is produced from ___________ (a) producer gas (b) water gas (c) coke (d) coal tar
- Describe how you can prepare a sample of hydrogen in the laboratory
- Discuss the reducing properties of this gas
- How do you test for hydrogen in the lab?
- Enumerate five uses of hydrogen
- Describe commercial preparation of hydrogen.
Read revised 2nd Edition Comprehensive Certificate Chemistry by G.N.C Ohia, et al pages 245-253
PRE READING ASSIGNMENT
Read about oxygen and its properties.
Explain how oxygen can be prepare in the laboratory and in the industry
- Revised 2ndedition comprehensive certificate chemistry G.N.C Ohia, et al
- New school chemistry for senior secondary by Osei Yaw Ababio.
- GENERAL PROPERTIES OF OXYGEN, ELECTRONIC CONFIGURATION AND BONDING CAPACITY OF OXYGEN
- LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN
- PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN.
- COMPOUNDS OF OXYGEN AND USES OF OXYGEN
PERIOD 1: GENERAL PROPERTIES OF OXYGEN
Oxygen is the most abundant element on earth. It is prepared in the laboratory by catalytic decomposition of Potassium trioxochlorate(V) or hydrogen peroxide. Industrially, it is prepared by the liquefaction of air followed by fractional distillation of liquefied air.
Oxygen, being strongly electronegative, is chemically very reactive. It reacts with most metals to form basic oxides which are ionic, they also reacts with most non- metals to form acidic oxides which are covalent molecules and they reacts with hydrocarbons, fuels[to form CO2 and H2O. It rekindles a glowing splint to indicate its presence in any place.
The oxides of oxygen can be classified into basic, acidic, amphoteric and neutral oxides. Peroxide is prepared by the action of a dilute acid on the peroxides of certain metals. It is a strong oxidizing agent. However, in the presence of more powerful oxidizing agents, ozone, O3, is an unstable allotrope of oxygen. The ozone layer in the atmosphere acts as a protective shield by preventing too much ultra-violet radiation from falling on earth and harming living organism.
Electronic Structure and Bonding Capacity Of Oxygen
Oxygen is an element in group (VIA) of the periodic table. Its atomic number is 8, and has an electronic configuration of 1S2 2S2 2P4 ————-Electronic structure
Thus, oxygen forms a complete octet by either accepting two electrons from a donor to form O2-in an ionic substance, or by sharing two electrons with other atoms to form a covalent substance. At room temperature and pressure, oxygen exists as a discrete gaseous diatomic molecule, O2 the two toms are joined together by double covalent bond, O=O.
- What is the name of the most abundant element on earth?
- Enumerate the main classes of oxides of oxygen
- Oxygen belongs to which group in periodic table.
- What is the atomic number of oxygen?
- Write electronic structure of oxygen.
PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN
There are two general and common methods for the laboratory preparation of oxygen
- Thermal decomposition of salts containing anions rich in oxygen, e.g. Potassium trioxochlorate(v) KClO3(s).
The equation for the reaction is given as shown below.
2KClO3(s) KCl(s) + 3O2(g)
- Decomposition of hydrogen peroxide: In this case, no heat is applied to the decomposing substance, H2O2,but immediately, the MnO2 touches H2O2, effervescence occurs releasing the gas oxygen as seen in the equation below.
2H2O(l) 2H2O(l) + O2(g)
Dry oxygen gas is obtained by passing it through a woulf [wash] bottle containing conc. H2SO4; the gas is then collected by downward delivery (or upward displacement of air), since pure oxygen is slightly denser than air.
Oxygen is produced, in large quantity from the following sources.
- From liquefied air: Oxygen is obtained industrially from atmospheric air by liquefaction, followed by fractional distillation of the liquefied air.
- Atmospheric air is purified by the removal of Carbon(IV) oxide, water vapour and dust.
- The purified air is compressed at a pressure of about 200 atmospheres, heated and then cooled. It is then allowed to expand suddenly, for further cooling.
- By successive heating and cooling, the pure air becomes liquefied at about -200[73k]. This process is called LIQUEFACTION.
- The liquefied air is then fractionated by boiling. Nitrogen, being more volatile, boils first at – 196[77k], leaving oxygen, which is about 99.5% pure. This separation technique is called FRACTIONAL DISTILLATION.
Liquefied oxygen is usually stored in cylinders for medical and industrial use.
- By electrolysis: Oxygen, like hydrogen is obtained during the electrolysis of dilute H2SO4.
- Statetwo main processes involved in the manufacture of oxygen from air.
- Outline industrial production of oxygen from air.
PERIOD 3: PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN
- Pure oxygen is colourless, odourless and tasteless.
- It is slightly denser than air.
- It is slightly soluble in water.
- It is a diatomic (O2) gas that is neutral to litmus paper.
- It boils (turn to gas) at -1830C and solidifies at -2250C
- Reaction with metals: Metals such as Na, K, Ca, Mg, Al, Zn burn brightly in oxygen. Metals such as silver, Gold and platinum do not react with oxygen. Oxides of metals are generally basic. e.g.
4Na(s)+ O2(g) 2Na2O(g)
- Reaction with non-metals: Some burning non-metals when lowered into a jar of oxygen, burn to form acidic oxides or acid anhydrides which when dissolved in water form acidic solutions. E.g.
CO2(g) + H2O(l) H2CO3(aq)
- Test for oxygen:Oxygen is identified by its ability to rekindle a glowing splint. Nitrogen (I) oxide does this as well but is distinguished from oxygen by its pleasant sickly smell while oxygen is odourless. Oxygen also reacts with nitrogen(II)0xide to give brown fumes of nitrogen(IV)oxide which nitrogen(I)oxide does not do.
NO (g) + O2(g) NO2(g)
Reaction of oxygen:
Oxidation and combustion:
Many compounds are oxidized when heated in oxygen (combustion). E.g. all hydrocarbons burn in oxygen to form carbon (iv) oxide and water, sulphides burn in oxygen to give sulphur (iv) oxides.
- With carbon
C(s) + O2(g) CO2(g)
- With sulphur
S(s) + O2(g) SO2(g)
- With phosphorus
4P(s) + 5O2(g) P4O10(s)
- Formation of water: Hydrogen burns violently in oxygen with a pale –blue flame, to produce water.
2H2(g) + O2(g) 2H2O(l)
- Formation of Ozone: When a silent electric discharge is passed through oxygen, gaseous ozone, O3, (trioxygen) is formed. The reaction is reversible:
3O2(g) ⇌ 2O3(g)
Ozone is an allotrope of oxygen. Allotropes are two or more different forms of the same element, in the same physical state. The phenomenon is called allotropy. Other elements that exhibits allotropy are sulphur, carbon and phosphorous.
- Write two equations for each, showing reaction of oxygen with metal and with non- metal.
- Enumerate three physical properties of oxygen
- List five chemical properties of oxygen.
- Mention the allotropes of oxygen.
PERIOD 4: COMPOUNDS OF OXYGEN
Binary Compounds of Oxygen- Classification of Oxides
Based on their acid –base properties, there are four classes of oxides of elements in Periods 2 and 3: acidic, basic, amphoteric and neutral.
Acid oxides: These are of non-metals which dissolve in water to form acidic solution. And react with base to form salt and water. Examples of acid oxides are P5O10, NO2, SO2, SiO2 etc. They are called acid anhydride. E.g.
CO2 +NaOH Na2CO3 + H2O
SO3 + 2KOH K2SO4 + H2O
NOTE: SiO2 is insoluble in water
Basic oxides: They are metallic oxides that are basic in nature because they react with acids to form salt and water only. Examples are K2O, MgO, CaO, Li2O etc. Soluble basic oxides are called alkali. E.g.
Na2O(g) + H2O(l) 2NaOH(aq)
Na2O(s) + 2HCl(aq) 2NaCl(aq) + H2O(l)
Amphoteric oxides: These are oxides that behave both like acidic and basic oxides. They react with both acid and base E.g. ZnO, Al2O3, PbO etc
ZnO(s) + H2SO4(aq) ZnSO4 + H2O(l)
ZnO + 2NaOH + H2O Na2Zn(OH)4
Neutral oxides: They are neither acidic nor basic in character. E.g. water, CO, N2O
Peroxide oxides: These are higher oxides where O-O bond is present. They give hydrogen peroxide when reacted with a dilute acid. E.g. Barium peroxide BaO2, Calcium peroxide CaO2, Sodium peroxide Na2O2, Hydrogen peroxide H2O2 (most common).
USES OF OXYGEN
- It is used in oxy-hydrogen for welding and cutting of metals. A mixture of hydrogen and oxygen can burn to produce a temperature of 2,500
- In oxy- ethyne [oxy-acetylene] flame for welding and cutting of steel. The reaction is highly exothermic.
- In respiration by plants and animals.
- As breathing aids in hospitals, high altitude flying and sea- dividing.
- In steel production by Linz- Donawitz [L-D] process.
- Liquefied oxygen is used in explosives, and as a rocket fuel
The Ozone Layer and Green House Effect
The ozone layer or ozone shield is a region of Earth‘s stratosphere that absorbs most of the Sun‘s ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically. It has been ascertained through observation from satellites, that the ozone layer has been depleted more over the Antartic and there is now the creation of ‘ozone hole’. This depletion or reduction in the levels of ozone in the ozone layer has caused worldwide changes in climate and sea levels caused by an increases warming of the atmosphere due to release of gases, principally, carbon(IV) oxide, CO2, in what is termed ‘Green house effect’. Green house gases e.g. CO2, water vapour, chlorofluorocarbons are transaparent to short wave radiation, but absorb radiation at certain long wavelengths. Thus, the gases form a blanket, trapping out-going heat, much as the glass or plastic does in a green house, thereby leading to rising sea levels and general atmospheric warming, as well as melting of ice and changes in vegetation. This has led to the problems of desertification and flooding.
- State three uses of oxygen.
- Define four types of oxide with one example each.
- In which group is oxygen in the periodic table? (a) IV (b) VI (c) VII (d) IV
- Which of the following is an allotrope form of oxygen? (a) oxide (b) Ozone (c) diamond (d) graphite
- Oxygen is prepared by heating. (a) Na2CO3(b) KClO3(c) K2SO4 (d) H2S
- The existence of two or more forms of the same element in the same physical state is known as. (a) Isotopic (b) allotropy (c) oxides (d) homologous.
- Amphoteric oxides are oxides which (a) react with neither acids nor alkalis (b) react with both acids and alkalis (c) react with acid only (d) react base only.
- What is allotropy? Name an allotrope of oxygen.
- Name the four classes of oxygen and give example of each class.
- Describe the commercial preparation of oxygen.
- Describe simple test to distinguish between oxygen and nitrogen(I)oxide
- Name the product formed when the following are burnt in oxygen:
- Carbon (ii) sulphur (iii) phosphorous (iv) magnesium.
PRE READING ASSIGNMENT
Read about halogens.
Describe the manufacturing of chlorine by the electrolysis of brine. State clearly the products liberated at the various electrodes and why these products were preferred.
- ELECTRONIC CONFIGURATION OF HALOGENS, PHYSICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP.
- CHEMICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP
- USES OF HALOGENS AND THEIR COMPOUNDS.
PERIOD 1 AND 2: ELECTRONIC CONFIGURATION OF HALOGENS
Halogens are found in group (viii) of the periodic table and consist of fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At),.
The name halogen is of Greek origin meaning salt formers because they readily form salts from metals. Halogens are very reactive non- metals with remarkable similarities in properties. This is because each halogen atom has seven only one electron to attain the octet. They are strong oxidizing agents with varying oxidation Numbers. The halogens are highly electro negative elements. The halogens share electrons to form covalent compounds or accept electrons to form ionic compounds. It is the electronic configuration of halogens that accounts for their electronegative nature, oxidising ability and the fact that they form mainly single covalent bonds.
ELECTRO CONFIGURATION AND SOME PROPERTIES OF THE HALOGENS AND GRADATION OF THE PROPERTIES
|Atomic radius||Ionic radius||Electro-negativity||Electro-affinity|| Atomic|
|Fluorine [F]||9||[2,7] IS22S22P5||0.072||0.136||4.0||-3.35||19.0|
|Chlorine [Cl]||17||[2,8,7] IS22S2 2p63S23P5|
PHYSICAL PROPERTIES OF THE HALOGENS
|Relative Atomic Mass||19||25.5||79.9||126.9|
|Physical state at 20||Gas||Gas||Liquid||Solid|
|Colour||Pale yellow||Greenish yellow||Dark-red||Black|
|Melting point (). Boiling point (||-220||-101||-7||113|
|Solubility in water(g per 100g of water)||Reacts readily with water||0.59||3.6||0.018|
- What is the atomic number of chlorine?
- With the knowledge of atomic number, draw the electronic configuration of chlorine.
- What is the colour of chlorine gas?
PERIOD 3: CHEMICAL PROPERTIES AND GRADATION DOWN THE GROUP
The chemical reactivity of the halogens decreases down the group from fluorine to iodine. The halogens are good oxidising agents and their oxidising power decreases from fluorine to iodine. The halogens try to attain the stable noble gas configuration either by sharing electrons or by accepting electrons. The following reactions illustrate the reactivity trend among the halogens.
- Halogens can react with metals as shown in the equations below
2Na(s) + F2(g) 2NaF(s)
- Halogens react with non-metals as shown below
C(s) + 2F2(g) CF4(s)
Xe+ 2F XeF4(s)
P4(s) + 6I2(s) 4PI3(s)
P4(s) + 6Cl2(g) 4PCl2(s)
P4(s) + 10Cl2(g) 4PCl5(s)
H2(g) + F2(g) 2HF(g)
H2(g) + Cl2(g) 2HCl(g)
Br2(g) + H2(g) 2HBr(g)
I2(g) + H2(g) 2HI(g)
The order of reacting is F2> Cl2>Br2>I2. The acid strength of the hydrogen halides follow the order:
The stability of Hydrogen halides decreases from chlorine to iodine: HCl>HBr>HI.
Chlorine is now an electron acceptor and so are other halogens and in so doing acts as oxidising agents.
2Na(s) + Cl2(g) 2Na+Cl–(s)
The order of decreasing power as oxidising agents is F2> Cl2>Br2>I2.
- More reactive halogen displaces the less reactive from aqueous solution
Cl2 + 2Br– 2Cl- + Br2
Cl2 + 2I– 2Cl– + I2
Br2 + 2I– 2Br– + I2
Iodine is a weak oxidizing agent.
- Reaction with water.
2F2(g) + 2H2O(l) 4HF(g) + O2
3F2(g) + 3H2O 6HF(g) + O3(g)
Cl2(g) + H2O(l) HCl(aq) + HClO(aq)
- Reaction with Alkalis
Cl2(g) + 2NaOH(aq) NaOCl(aq) + NaCl + H2O
3Cl2(aq) + 6NaOH(aq) NaClO3(aq) + 5NaCl + 3H2O(l)
Bromine and iodine react in a similar manner to form the oxobromate(v) and iodated(v) ions.
3Br2(aq) + 6KOH(aq) KBrO3(aq)
3I2(aq) + 6KOH(aq) KIO3(aq) +5KI(aq) + 3H2O(l)
- Give one for each equation of reaction to demonstrate the reaction of Cl2, Br2, I2and F2
PERIOD 4: USES OF HALOGENS AND THEIR COMPOUNDS
- Fluorine is used in rocket propulsion and in making Uranium(iv) fluoride. It is also used in making fluorocarbon compounds which are used as refrigerant, aerosol propellant, anaesthetics and fire extinguisher and fluids. The flouoro- carbons contain only carbon and fluorine and are extremely inert and also are used as polytetrafluoroethene[PTFE] with the trade name Teflon in making valves, seals, gaskets, electrical insulators among others.
- CHLORINE: is used as oxidant in the manufacture of bromine and as bleach and germicide in treatment of water. Chlorine is used in production of HCl (hydrogen chloride) in commercial quantity, in the production of fabrics and papers and also insecticides. (e.g DDT)(3) Iodine dissolved in alcohol or potassium iodide [KI] is used as antiseptic for cuts and scratches.
- HYDROCHLORIC ACID which is one of the most laboratory acid, is used to remove rust from steel sheet before galvanizing.
- SODIUM OXOCHLORATE (I) [NaCLO] is used as disinfectant and for bleaching in laundries.
- SODIUM OXOCHLORATE (1) decomposes on warming to sodium oxochlorate(v), NaCLO3 which is used as weed killer.
- Tetrachloromethan and trichloroethene are degreasing solvents.
- Polychloroethene is used in making plastics
- Dettol is used as disinfectant and antiseptics.
- Dichlorodiphenyltrichloroethane (DDT) and benezehexachloride are used as pesticides
- Bromine finds application in the manufacture of dyestuffs and in making silver bromide used in photographic materials.
Enumerate five uses of halogens you know
- What is the atomic number of chlorine? A. 35 B. 53 C. 82 D. 17
- 2, 8,18,7 is the electronic configuration of A. F B. Cl C. Br D. I
- Why is the preparation of halogens carried out in a fume cupboard? A. they are odourless B. they are poisonous C. They are colourless D. They are harmless.
- In halogens the order of decreasing power as oxidising agents is
- F2>Cl2>Br2>I2B .Cl2>F2>Br2>I2C. Br2>F2>I2>Cl2 D. Br2>Cl2>F2>I2
- In halogens, melting points and boiling points increase with an increase in A. Molecular mass B. Valence C. oxidation number D. Atomic number
- Name two natural compounds of halogens.
- State the similarities in chemical properties of halogens giving balanced reactions.
- Write on the following giving balanced reaction examples. Halogen reaction with
(i) water (ii) iron (iii) alkali
- (a) What is the atomic number of chlorine? (b) Why is the preparation of halogens carried out in a fumed cupboard?
- What are the chemical properties of halogens?
- Read 2ndedition comprehensive certificate chemistry by by G.N.C Ohia, et al, pages 272-284
PRE READING ASSIGNMENT
Read about the uses of halogens and laboratory and chemical preparation of chlorine
- Write the formulae of the following.
(i) Chloroform (ii) iodoform (iii) Carbon tetrachloride (iv) fluorine molecule
- What are the uses of Carbon tetrachloride?
- 2ndEdition Comprehensive Certificate Chemistry By By G.N.C Ohia, et al.
- New school chemistry for senior secondary schools by Osai Yaw Ababio reversed by L.E.S Akpanisi Herbert Igwe.
- PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)
- PROPERTIES OF CHLORINE (PHYSICAL AND CHEMICAL)
- HYDROGEN CHLORIDE GAS: LABORATORY PREPARATION PROPERTIES AND USES,
- TEST FOR HCL GAS AND FOUNTAIN EXPERIMENT.
PERIOD1: PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)
In the laboratory chlorine is prepared by the oxidation of concentrated hydrochloric acid with manganese (IV) oxide. The mixture is heated to obtain a greenish- yellow gas (chlorine).
MnO2(s) + 4HCl (aq) MnCl2(aq) + 2H2O + Cl2
Chlorine is prepared industrial by the electrolysis of brine and molten metallic chlorides
Describe the laboratory preparation of chlorine
PERIOD 2: PHYSICAL PROPERTIES OF CHLORINE
- It is a greenish-yellow gas with an unpleasant choking smell.
- It is denser than air.
- It is slightly soluble in water.
- It is poisonous.
The chemical properties od chlorine have been discussed under the general properties of halogens. Let’s discuss the oxidizing properties of chlorine.
- Chlorine oxidizes hydrogen sulphide to yellow sulphur.
Cl2 + H2S 2HCl + S
- Bleaching property of chlorine
Chlorine bleaches by oxidation. When chlorine dissolves in water, it forms hydrochloric acid and oxochlorate (i) acid (chlorine water).
Cl2 + H2O HCl + HOCl
In bleaching oxochlorate (i) acid gives out oxygen atom. The oxygen atom then bleach the material by oxidation. This bleaching action is permanent because the material cannot be re-oxidize by atmospheric oxygen.
- State four physical properties of chlorine.
- Describe the bleaching action of chlorine.
PERIOD 3: HYDROGEN CHLORIDE GAS-PREPARATION, PROPERTIES AND USES.
Hydrogen chloride is prepared in the laboratory by the action of concentrated tetraoxosuphate (vi) acid on sodium chloride. The gas is dried by passing it through concentrated tetraoxosulphate (vi) acid and collected by downward displacement of air.
NaCl(s) + H2SO4(aq) Na2SO4(aq) + HCl(g).
Dissolution of hydrogen chloride in water gives hydrochloric acid.
PHYSICAL PROPERTIES OF HYDROGEN CHLORIDE
- It is a colourless gas with sharp irritating smell.
- It is denser than air.
- It is very soluble in water.
- It turns moist blue litmus paper red.
- It is soluble in non-polar solvent like methylbenzene. It solution in methylbenzene cannot conduct electricity because it does not undergo ionization when dissolved in methylbenzene. But when dissolved in water, it undergoes ionization and so conduct electricity becase of the presence of free mobile ions.
CHEMICAL PROPERTIES OF HYDROGEN CHLORIDE
- It reacts with active metals to liberate hydrogen gas e.g
Zn(s) + 2HCl(g) ZnCl2(s) + H2(g)
- It reacts with ammonia to form a dense white fume of ammonium chloride.
HCl(g) + NH3(g) NH4Cl(s)
- Hydrochloric acid (obtained when hydrogen chloride dissolved in water) reacts with metallic trioxocarbonate (iv) or metallic hydrogentrioxocarbonate (iv) to liberate carbon (iv) oxide.
2HCl(aq) + Na2CO3(s) 2NaCl(aq) + H2O(l) + CO2(g)
- Hydrochloric acid (obtained when hydrogen chloride dissolved in water) precipitates silver chloride from solution.
AgNO3(aq) + HCl(aq) AgCl(s) + HNO3(aq)
USES OF HYDROGEN CHLORIDE GAS AND HYDROCHLORIC ACID
- It is used for the synthesis of vinyl chloride which is used for the manufacture of plastics.
- Hydrochloric acid is used for pickling of metals prior electroplating.
- Hydrochloric acid is for the synthesis and analysis of many compounds.
- State three physical properties of hydrogen chloride.
- Mention three chemical properties of hydrochloric acid.
- State four uses of hydrogen chloride.
PERIOD 4: TEST FOR HCL GAS AND FOUNTAIN EXPERIMENT.
- GENERAL PROPERTIES OF NITROGEN–GROUP VA ELEMENTS, LABORATORY AND INDUSTRIAL PREPARATION OF NITROGEN,
- PROPERTIES AND USES OF NITROGEN
- COMPOUND OF NITROGEN – AMMONIA- LABORATORY AND INDUSTRIAL PREPARATION
- PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT
PERIOD 1: GENERAL PROPERTIES OF NITROGEN – GROUP V ELEMENTS
Nitrogen and other group VA elements are non-metals and show two common valences of 3 and 5. They are electron acceptors and both form several acidic oxides. They also form similar hydrides and chloride e.g. Nitrogen and phosphorus form N2O3 and P4O6, N2O5 and P4O10, NH3, PH3, NCl3 and PCl3
Properties of VA elements
|Outer electron configuration||2s22p6||3s23p3||3d104s2 4p3||4d104s25p3||4f15d106s26p3|
W = white, gr = grey, p = 28 atmospheres, r = red, s = sublimes
LABORATORY AND INDUSTRIAL PREPARATION OF NITROGEN
- Laboratory preparation of nitrogen from air
Atmospheric air is passed through aqueous NaOH, in order to absorb carbon (iv) oxide.
2NaOH(aq) + CO2(g) Na2CO3(aq) + H2O
It is then passed over red-hot copper metal in a combustion tube in order to remove oxygen.
Cu(s) + O2(g) 2CuO(s)
The residual gas collected over water is Nitrogen contaminated with small quantity of noble gases. Other methods of preparing nitrogen in the laboratory include:
Preparation from Ammonia gas.
CuO(s) + NH3(g) 3Cu(s) + H2O(g) + N2(g)
From ammoniumdioxonitrate (iii)
NaNO2(aq) + NH4Cl(aq) NH4NO2(aq) + NaCl(aq)
- Industrial preparation of nitrogen
Nitrogen is produced commercially from fractional distillation of liquefied air.
PROCEDURE: Carbon (iv) oxide is removed from air. This air is liquefied by subjecting it to succession compression and cooling processes.
Nitrogen is collected first after distillation before oxygen because it has a lower boiling point than oxygen.
Nitrogen is stored in steel in steel cylinders and sold as liquid nitrogen or as the compressed gas.
- Describe how nitrogen can be obtained from ammonia.
- Name the reagents necessary for the laboratory preparation of nitrogen from air.
- How is nitrogen obtained commercially?
PERIOD 2 : PROPERTIES AND USES OF NITROGEN
- Pure nitrogen is colourless, odourless and tasteless
- It is insoluble in water
- It is lighter than air.
- It has no effect on litmus paper
- Combustion: Nitrogen gas is generally unreactive at ordinary temperatures and pressures. It does not burn and does not support burning. It extinguishes a lighted splint.
- Reaction with metals. Magnesium ribbon burns in air to produce a mixture of magnesium oxide and magnesium nitricide, a white solid.
2Mg(s) + O2(g) MgO(s)
3Mg(s) + N2(g) Mg3N2(s)
Magnesium nitride decomposes on addition of water to liberate ammonia gas
Mg3N2(s) + 6H2O(l) 3Mg(OH)2(aq) + 2NH3(g)
- (a) Reaction with non-metals: (a) under conditions of high temperatures and pressures, and in the presence of finely divided iron as catalyst, nitrogen combines with hydrogen, to produce ammonia. The reaction in reversible.
N2(g) + 3H2(g) 2NH3(g)
(b) Nitrogen combines with oxygen at high temperature and pressure to produce Nitrogen (ii) oxide, an unstable colourless and odourless gas. The reaction is reversible.
N2(g) + O2(g) ⇌ 2NO(g)
USES OF NITROGEN
- In the Haber process in production of ammonia.
- Liquid nitrogen is used as a refrigerant.
- Due to its inertness and because it does not support combustion it is used for the following purposes:
(a) For prevention of fire
(b) As a diluents: to reduce combustion (nitrogen is responsible for the low heating value of producer gas, and the low combustion rate of atmospheric oxygen.
(c) Nitrogen provides inert atmosphere for food processing and packaging, and during some chemical reactions.
The continuous circulation of nitrogen between the free gaseous nitrogen in the atmosphere and the combined nitrogen in the proteins of the living tissues is known as the Nitrogen circle.
Nitrogen is an essential element in the formation of proteins in plants and animals. Unfortunately, it cannot be used directly in its free gaseous state, except in the form of trioxonitrate (v) salts (Nitrate). There are various processes through which atmospheric nitrogen is converted into trioxonitrate (v) salts in the soil, the process are called FIXATION OF FIXING OF NITROGEN.
- When there is a thunder storm or lightning electric discharges are produced, during which atmospheric nitrogen and oxygen combine to form unstable and colourless nitrogen (ii) oxide
N2(g) + O2(g) 2NO(g)
The nitrogen (II) oxide readily combines with more oxygen, to form brown fumes of nitrogen (iv) oxide.
2NO(g) + O2(g) 2NO(g)
The nitrogen (iv) oxide dissolves in rain water in the presence of oxygen, to produce a very dilute solution of trioxonitrate (v) acid, HNO3, which falls as acid rain.
4NO2(g) + 02(g) 2NO2(g)
- Plants absorb trioxnitrate (v) salts through the roots for the formation of flesh, and the excess is excreted as urea-in urine and faeces. When plants and animal die and decay, the bacteria in the soil decompose the proteins into organic compounds of nitrogen which are then converted into ammonia and ammonium salts, by PUTREFYING bacteria. A portion of the ammonium salts, in alkali medium, is oxidized into trioxonitrate(v) salt by NITRIFYING bacteria, while the remaining portion in acidic medium is oxidized to nitrogen, by DENTRIFYING bacteria. The nitrogen eventually goes back into the atmosphere. This is the process that usually compensate for the lost of atmospheric nitrogen.
- Manure and nitrogeneous fertilizers are being added to the soil periodically, in order to replace nitrogen that has been used up by crops or plants. The nitrogen cycle operates in nature such that the percentage of nitrogen in the atmosphere remains constant.
THE NITROGEN CYCLE
- Name one process, which converts atmospheric nitrogen to nitrate (v) in the soil.
- Explain the formation of trioxonitrate (v) acid in the nitrogen cycle.
PERIOD 3: COMPOUNDS OF NITROGEN-AMMONIA LABORATORY AND INDUSTRIAL PREPARATION
OXIDES OF NITROGEN
The common oxides of nitrogen are:-Dinitrogen(i) oxide, N2O- Nitrogen (ii) oxide, NO. Nitrogen (iv) oxide, NO2, others are dinitrogen(iii) oxide, N2O3, a pale blue liquid at room temperature and dinitrogen(iv) oxide, N2O4, a yellow liquid below the room temperature and dinitrogen(v) oxide N2O5 that exists as an unusual white solid at room temperature.
INDUSTRIAL PRODUCTION OF AMMONIA
The Haber process: Ammonia is manufactured from its constituent elements by a process devised by a German chemist, Fritz Haber (1914). The raw materials used are: nitrogen (obtained from water gas or natural gas).A mixture of dried nitrogen and hydrogen in the ratio 1:3 by volume is subjected to a high pressure of 200 – 250 atmosphere, at about 450 and in the presence of finely divided iron as the catalyst; the reaction is exothermic and reversible
N2(g) + 3H2(g) 2NH3(g)
Under these conditions, about 20% ammonia is produced.
Successive heating and cooling under pressure liquefy the ammonia gas produced and the uncombined nitrogen and hydrogen are recycled. The flow chart for the production of ammonia is shown
LABORATORY PREPARATION OF AMMONIA:
Ammonia is prepared in the laboratory by heating a mixture of ammonium salt and non-volatile base. Calcium hydroxide is preferred to sodium hydroxide because calcium hydroxide is cheap and non-deliquescent. Heating a mixture of ammonium chloride and calcium hydroxide produces ammonia gas. The drying agent for ammonia is calcium oxide (quick lime). Concentrated tetraoxosulphate (vi) acid and calcium chloride are not used to dry ammonia because they react with ammonia to form salts
NH4Cl + Ca(OH)2 CaCl2 + H2O + NH3
- State the type of chemical bond between nitrogen and hydrogen atoms in a molecule of ammonia.
- In the industrial production of ammonia.
- What name is given to the process?
- State one source of each of the starting material.
- What are the operating temperature and pressure?
PERIOD 4: PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT
PHYSICAL PROPERTIES OF AMMONIA:
- It is a colourless gas with choking smell.
- It is very soluble in water.
- In large quantities, ammonia is poisonous.
- It is 1.7 times less dense than air
- It turns moist red litmus paper red.
CHEMICAL PROPERTIES OF AMMONIA
- Ammonia burns in oxygen producing steam and nitrogen
4NH3 + 3O2 2N2 + 6H2O
Ammonia reacts with platinium- rhodium catalyst to form nitrogen (ii) oxide.
4NH3 + 5O2 4NO + 6H2O
- Ammonia reduces copper (ii) oxide
2NH3 + 3CuO 3Cu + 3H2O + N2
- Ammonium precipitates many metallic ions from solution as insoluble hydroxides.
FeSO4(aq) + 2NH3(aq) + 2H2O(l) Fe(OH)2(s) + (NH4)2SO4(aq)
USES OF AMMONIA
- Ammonia is used in refrigeration, since it can be liquefied easily.
- In softening water used in laundry, to prevent wastage of soap.
- As a domestic cleaner- to neutralize as in sweat.
- In treating insect stings- to neutralize methanoic acid injected by the insects
- In the production of plastics by polymerization
- In the production of ammonium salts. Fertilizer and trioxonitrate(v) acid.
- As a precipitating regent for the identification of cations in solutions.
TEST FOR AMMONIA GAS
Place any ammonia salt in a test tube, add any alkali and heat the mixture. A colourless gas with choking smell is given off. The gas turns moist red litmus paper to blue and produces dense white fumes with hydrogen chloride gas (from concentrated HCl reagent bottle. The gas is ammonia
- State four physical properties of ammonia
- With chemical equation, describe how ammonia is used to precipitate Pb2+and Zn2+
- Which of the following contains the highest number of molecules at s.t.p?(Avogadro’s constant)= 6.02 × 1023mol-1(a) 1.0g of H2 (H2=2) (b) 4.0g of N2(N2 = 28) (c) 8.0g of O2 (O2=32) (d) 16.0g of O3 (O3= 48)
- The laboratory preparation of nitrogen from air requires the removal of (a) carbon(iv)oxide (b) water vapour (c) oxygen and carbon (iv)oxide (d) carbon (iv) oxide, oxygen and water vapour
- Nitrogen combines reversibly with hydrogen under (a) catalyst (b) high voltage electric spark (c) the presence of traces of NO2(d) platinium
- Nitrogen combines directly with metals except. (a) Cu (b) Mg (c) Ca (d) Al
- Oxidation of Nitrogen in Mg3N2is (a) -3 (b) +3 (c) -2 (d) +2
- Outline the laboratory preparation of Nitrogen from atmospheric air.
- (a) State two physical properties of Nitrogen (b) Name the process used in the commercial production of nitrogen.
- Describe the laboratory preparation of nitrogen with the following (i) magnesium (ii) oxygen
- (i) What is the percentage by volume of nitrogen in air? (ii) Calculate the amount, in mole of magnesium nitride that can be obtained from 3.0g of magnesium (Mg =24)
- (a) State how nitrogen resemble or differ from NH3. (b) How does nitrogen resemble or differ from CO2in its reaction with each of the following (i) litmus (ii) A burning candle (iii) burning magnesium
WEEK 8 TOPIC
- NITROGEN: COMPOUNDS OF NITROGEN: TRIOXONITRATE(V) ACID –
LABORATORY PREPARATION AND PHYSICAL PROPERTIES
- CHEMICAL PROPERTIES OF TRIOXONITRATE (V) ACID
- USES OF TRIOXONITRATE (V) ACID
- TRIOXONITRATE(V) SALTS- ACTION OF HEAT, TEST FOR TRIOXONITRATE(V)
PERIOD 1: NITROGEN: COMPOUNDS OF NITROGEN: TRIOXONITRATE(V) ACID –
LABORATORY PREPARATION AND PHYSICAL PROPERTIES
LABORATORY PREPARATION OF TRIOXONITRATE (V) ACID
Trioxonitrate (v) acid is prepared by heating solid sodium trioxonitrate (v) with concentrated tetraoxosulphate (vi) acid.
NaNO3 + H2SO4 HNO3 + NaHSO4
The apparatus used is completely made of glass because rubber and cork are attack by trioxonitrate (v) acid. The trioxonitrate (v) acid produced in this case is yellow in colour due to the slight decomposition of the acid by heat to produce reddish-brown gas (nitrogen (iv)) which then dissolve in the acid to impart the yellow colour.
4HNO3 H2O + 4NO2 + O2
PHYSICAL PROPERTIES OF TRIOXONITRATE (V) ACID
- It is corrosive and readily destroys organic materials.
- It turns blue litmus paper red.
- It is a colourless liquid which fumes in air on exposure.
- Explain why trioxonitrate (v) acid produced in the laboratory is yellow in colour.
- Why is all-glass apparatus used in the preparation of trioxonitrate (v0 acid.
- State three physical properties of trioxonitrate (v0 acid.
PERIOD 2: CHEMICAL PPROPERTIES OF TRIOXONITRATE (V) ACID
- Reaction as an acid:
(a) It reacts with base to form salt and water
HNO3 + NaOH NaNO3 + H2O
(b) It reacts with trioxonitrate (v) to liberate carbon (iv) oxide
HNO3 + CaCO3 Ca(NO3)2 + H2O + CO2
- As an oxidizing agent:
(a) with metals: Trioxonitraye (v0 acid is a strong oxidizing agent and the oxidizing power of trioxonitrate (v) acid depends on its concentration. In concentrated form, it oxidizes certain metal to trioxonitrate (v) while the acid is reduced to nitrogen (iv) oxide and in moderately concentrated form it reduced to nitrogen (ii) oxide.
Cu + 4HNO3 Cu(NO3)2 + 2H2O + 2NO2
3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO
Lead, mercury and silver react in similar way to copper with the metal
Magnesium, zinc nad iron react with dilute trioxonitrate (v) acid to give ammonium trioxonitrate (v0 or nitrogen (i) e.g
4Zn + 10HNO3 4Zn(NO3)2 + 3H2O + NH4NO3
Aluminium and iron do not react with concentrated HNO3 due to initial formation of an oxide coating on the metal, which prevent further reaction.
(b) With non-metals: Hot concentrated tetraoxosulphate (vi) acid oxidizes non-metals to their oxides, which may dissolve in water to for the corresponding acids.
C + 4HNO3 CO2 + 2H2O + 4NO2
S + 6HNO3 H2SO4 + 2H2O + 6NO2
P + 5HNO3 H3PO4 + H2O + 5NO2
I2 + 10HNO3 2HIO3 + 4H2O + 10NO2
- Explain why metals can displace hydrogen from trioxonitrate (v0 acid.
- State three chemical properties of trioxonitrate (v0 acid
PERIOD 3: USES OF TRIOXONITRATE (V) ACID
- It is an important raw material for the manufacture of many useful trioxonitrate (v0 salts and organic nitro-compounds such as those used for making dyes. Explosives, fertilizers and drugs.
- It is used for making of nylon and terylene.
- It is useful oxidizing agent for many purposes in the laboratory.
State four uses of trioxonitrate (v0 acid.
PERIOD 4: TRIOXONITRATE(V) SALTS- ACTION OF HEAT, TEST FOR TRIOXONITRATE(V)
All trioxonitrate (v) salts are decomposed by heat.
(a) Trioxonitrate (v0 of sodium and potassium are decomposed to the dioxonitrate (iii) compound and oxygen.
NaNO3 NaNO2 + O2
(b) Trioxonitrate (v) of Zn, Cu, Fe, Mg, Ca, Pb and Al are decomposed to the oxide of the metal, nitrogen (iv) oxide and oxygen.
2Pb(NO3)2 2PbO + 4NO2 + O2
(c) Trioxonitrate (v) of Hg and Ag are decomposed to the metal, oxygen and nitrogen (iv0 oxide because the metal oxides are unstable to heat
2AgNO3 2Ag + 2NO2 + O2
TEST FOR TRIOXONITRATE (V0 IONS
BROWN RING TEST
Acidify an unkwon solution with dilute tetraoxosulphate (vi) acid, then add some freshly prepared iron (ii) tetraoxosulphate (vi) and shake. Then keep the test tube in a slanting position and carefully add some concentrated tetraoxosulphate (vi) acid down the side of the test tube. A brown ring will be formed ar the junction of the two liquid layers. This shows that the unknown contains trioxonitrate (v) ions. the brown ring is FeSO4.NO
- Nitrogen combines directly with metals except (a) Ca (b) Mg (c) Cu (d) Al
- Oxidation number of nitrogen in Mg3N2is (a) -3 (b) +3 (c) -2 (d) +2
- Hydride of nitrogen which is capable of turningred litmus blue make nitrogen to have an oxidation state of (a) +2 (b) -2 (c) +3 (d) -3
- Pyre trioxonitrate (v0 acid is colourless but the product of its laboratory preparation is yellow because of the presence of dissolved (a) sulphur (b) sulphur (iv) oxide (c) nitrogen (iv) oxide (d) nitrogen (ii) oxide
- Which of the following will not leave a solid residue when decomposed by heat? (a) (NH4)2SO4(b) NaNO3(c) Ca(NO3)2 (d) KNO3
- Explain what is observed when lead (ii) trioxonitrate (v) is heated.
- Explain why iron (ii) tetraoxosulphate (vi) is always prepared freshly whenever is to be used for analysis.
- Explain why trioxonitrate (v) acid is not used to acidify KMnO4solution.
PRE READING ASSIGNMENT
Read about allotropes of sulphur on page 381 of New School chemistry by Osei Yaw Ababio
Draw the nitrogen cycle in New School chemistry by Osei Yaw Ababio
- GENERAL PROPERTIES OF GROUP VIA ELEMENT
- ALLOTROPES AND USES OF SULPHUR
- COMPOUNDS OF SULPHUR- TRIOXOSULPHATE (IV) ACIDS AND ITS SALTS
- TETRAOXOSULPHATE (VI) ACID: INDUSTRIAL PREPARATION, REACTIONS AND USES.
PERIOD 1: GENERAL PROPERTIES OF GROUP VIA ELEMENT
Group VIA elements usually called oxygen family have the following properties
- They are made up of oxygen (O), sulphur (S), Selenium (Se) Tellurium (Te) and Polonium (Po)
- Oxygen gas is the first member of the group
- Sulphur comes as the second member of the group and it is a solid, followed by other members.
- They have six valence electrons.
- They gain two electrons usually from group I and II metals to attain octet structure or form negative divalent ions e.g. S2, O2
- They form covalent compounds with non-metals e.g. H —–O——–H in water and H—-S—–H , hydrogen sulphide
- Their oxidation states range from -2 in its compounds except peroxides like H2O2and K2O2 where oxygent has -1
ELECTRON STRUCTURE OF SULPHUR
Sulphur is represented with a symbol S, it has 16 atomic numbers. The electronic configuration is 2, 8,6. It is a P block element. Thus have its valence electrons in the p orbital Is2 2s2 2p6 3s23p4
The distribution of electrons into shell is given in the figure below:
Electronic configuration of sulphur
- Enumerate any five (5) general properties of group VIA elements.
- Explain briefly the electron structure of sulphur
PERIOD 2: ALLOTROPES AND USES OF SULPHUR
Sulphur exhibits the phenomenon of allotropy. Allotropy is the existence of an element in two or more different forms in the same physical state. The various forms are known as allotropes. The allotropes of sulphur are Rhombic (or – sulphur), Monoclinic or prismatic – sulphur), Amorphous sulphur (S- sulphur), Plastic sulphur
Rhombic and monoclinic sulphur are crystalline in nature and are actually the important allotropes.
- Rhombic sulphur (α- sulphur): free sulphur exists as allotrope at below 96. It has octahedral structure made up of S8 The colour is brightly yellow and has a melting point of 113and density of 2.08gcm-3
Rhombic sulphur is prepared by allowing a saturated solution of sulphur in carbon (IV) sulphide (carbon disulphide) in a test tube kept below C to evaporate slowly. Octahedral crystals will gradually deposit. This preparation should be done in a fume cupboard because of the poisonous and flammability of carbon disulphide
- Monoclinic sulphur (β– sulphur): It is the only stable allotrope between 96and 119 and consists of long, thin and needle shaped. The colour is amber. At room temperature it changes to rhombic sulphur crystals. Monoclinic sulphur has a melting point of 119oC and density of 1.98gcm-3
Monoclinic sulphur is obtained by cooling molten sulphur. Powdered sulphur is heated in a crucible till it melts into amber -coloured liquid. More sulphur is added, heated and stirred at the same time. This process is repeated until the crucible is filled with molten sulphur. It is then allowed to cool while a hard crust formed at the top. Piercing one or two holes through the crust and pouring off the remaining molten sulphur reveals a needle shaped crystals of monoclinic sulphur deposited on the sides of the crucible.
Rhombic sulphur monoclinic sulphur
- Amorphous sulphur: it is pale – yellow in colour and has no regular crystalline shape. It is prepared as a deposit when hydrogen sulphide is bubbled through water for a long time and the saturation exposed to air. It can also be prepared by the action of dilute HCl acid on trioxothiosulphate (v) solution
H2S (g) + O2(g) → 2H2O(g) + S(g)
S2O32-(aq) +2H+(aq) → 2H2O(l) + SO2(g) + S(s)
- Plastic sulphur: this is prepared by heating yellow sulphur until it boils in a test tube. The boiling sulphur is poured into cold water is seen to roll up into yellow ribbons which look like a plastic. It changes to rhombic sulphur after sometime. It is therefore said to be unstable.
- (a) What is allotropy? (b)(i) Name two allotropes of sulphur (ii) State two differences between them.
- Explain briefly, how Rhombic and monoclinic sulphur are obtained.
- Describe the formation of plastic sulphur and amorphous sulphur.
PROPERTIES OF SULPHUR
- Sulphur is a yellow solid existing in crystalline or amorphous
- It is non-metallic and exhibits allotropy.
- It sublimes to give flowers of sulphur.
- It is a non-conductor of heat and electricity.
- When heated in the absence of air, roll sulphur undergoes the following changes:
- at 1150C it forms amber – coloured liquid.
- at about 1150C the liquid becomes dark and discourse.
- near its boiling point, becomes mobile again and reddish brown in colour.
- at its boiling point of 440C it gives off a brown vapour, condensing this vapour on a cold surface gives flowers sulphur.
(i) Combustion in air: sulphur burns in air with a blue flame to produce sulphur (iv) oxide.
S(s) + O2(g) → SO2(g)
(ii) Reaction with metals: sulphur combines directly with metals to give the corresponding anhydrous sulphides
Fe(s) + S(s ) → FeS(s)
2Cu(s) + S(s) → Cu2S(s)
(iii) Reaction with non- metals: sulphur reacts with coke in the furnace to produce carbon (IV) sulphide
C(s) +2S(s) → CS2(l)
(iv). As a reducing agent: when powdered sulphur is warmed with concentrated H2SO4, it is oxidized to SO2, while its acid is reduced to SO2.
S(s) + H2SO4(aq) → 2H2O(l) + 3SO2(g)
USES OF SULPHUR
- Used in the production of tetraxosulphate (VI) acid.
- Used in vulcanizing rubber. It makes raw rubber to become hard, tough and elastic and hence, suitable for making tyres
- Used in the production of carbon (iv) sulphide used as a solvent and insecticides
- It is used in gun powder and matches, dyes tuffs fungicides, ointment and germicides
- Also used in the production of calcium hydrogen trioxosulphate (iv), Ca(HSO3)2used in bleaching wood pulp for making news prints
- (a) What is flower of sulphur (b) what are the products of reaction of sulphur with it concentrated H2SO4acid
- Mention three(3) physical and four (4) chemical properties of sulphur
- Itemize the uses of sulphur
PERIOD 3: COMPOUNDS OF SULPHUR- TRIOXOSULPHATE (IV) ACIDS AND ITS SALTS
Trioxosulphate (IV) acid is a dibasic acid which is obtained by dissolving sulphur (IV) oxide in water.
LABORATRY PREPARATION OF TRIOXOSULPHATE (IV) ACID
It is prepared by the action of dilute hydrochloric acid on heated sodium trioxosulphate (iv) to produce sulphur (iv) oxide which is then dissolved in water.
Equations of the reactions
(a) Na2SO3(s) + 2HCl(aq) → 2NaCl(qg) + SO2 (g) + H2O(l)
(a) SO2 (g) + H2O (l) → H2SO3 (aq)
Sulphur (IV) oxide is the acidic hydride of trioxosulphate (IV) acid.
PHYSICAL PROPERTIES OF TRIOXOSULPHATE (IV) ACID
- It isa colourless liquid, which smells strongly of SO2.
- 2. It turns blue litmus paper red.
- It mixed readily with water.
- It has an irritating and choking smell.
CHEMICAL PROPERTIES OF TRIOXOSULPHATE (IV) ACID
- Trioxosulphate (iv) acid is a weak dibasic acid. In the presence of a limited amount of sodium hydroxide an acid salt, sodium hydrogen trioxosulphate (IV) is formed.
2NaOH (aq) + H2SO3 (aq) → Na2SO3 (aq ) + 2H2O(l)
However, when the alkali, sodium hydroxide, is in excess, the normal salt sodium trioxosulphate (IV) is produced. That is, complete neutralisation takes place.
NaOH (aq )+ H2SO3(aq)→ NaHSO3(aq), + H2O(l)
- It is oxidized in air t tetraoxosulphate (VI)acid. H2SO4(aq)+ O2(g) →2H2SO4(aq)
- Reducing properties
It is a strong reducing agent. It decolourises the purple colour potassium tetraoxomanganate (vii) solution, and changes the colour of potassium heptaoxodichromate (VI) from orange to green.
- Bleaching properties:dyes are bleached by aqueous solution of trioxosulphate (IV) acid. It bleaches by reduction. Material bleached by trioxosulphate(iv) acid and sulphur (iv) oxide temporal, it can be re-oxidized by atmospheric oxygen.
USES OF TRIOXOSULPHATE (IV) ACID
- It is used for bleaching.
- It is also used as a germicide.
TRIOXOSULPHATE (IV) SALTS
Trioxosulphates (IV) are the salts of trioxosulphate (IV) acid.
LABORATORY PREPARATION OF TRIOXOSULPHATE (IV) SALTS
- By the action of trioxosulphate (iv) on excess alkali. Sodium hydroxide is used.
H2SO3 (aq) + NaOH (aq) → Na2SO3(aq) + 2H2O(l)
This is a neutralization reaction.
- Precipitation of an insoluble trioxosulphate (IV) from the solution of its metallic salt by sulphur (iv) oxide.
SO2 (g) +2H2O (l) +ZNNO3 (ag) → ZnSO3(s) +HNO3 (l)
PHYSICAL PROPERTIES OF TRIOXOSULPHATE (IV) SALTS
Most of the trioxosulphates (IV) are insoluble in water but the trioxosulphate (IV) of calcium; ammonium, potassium and sodium are soluble in water.
CHEMICAL PROPERTIES OF TRIOXOSULPHATE (IV) SALTS
- They liberate sulphur (IV) oxide on reaction with aqueous hydrochloric acid e.g. Na2CO3,
Na2CO3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O (l) +SO2 (g)
- When exposed to air trioxosulphate (IV) salts are slowly oxidised to tetraoxosulphate (VI) salts.
- On addition of barium chloride solution into solution of trioxosulphate (IV) white precipitate of barium trioxosulphate (IV) which is soluble in dilute hydrogen chloride (HCl) is formed.
BaCl2 (aq) + Na2SO3 (aq) → BaSO3(s) + 2NaCl (aq)
TEST FOR TRIOXOSULPHATE (IV) SALT
- On warming with dilute hydrochloric acid sulphur (IV) oxide is given off.
- Add solution of barium chloride to the solution of the substance suspected to be trioxosulphate (IV). Any white precipitate (barium trioxosulphate (IV)), soluble in dilute hydrochloric acid confirms the presence of a trioxosulphate (IV) ion e.g. Na2SO3.
BaCl2 (aq) + Na2SO3 (aq) → 2NaCl (aq) + BaSO3(s)
DIFFERENTIATING TRIOXOSULPHATE (IV) AND TETRAOXOSULPHATE (VI) IONS
For trioxosulphate (IV), the white precipitate (barium trioxosulphate (IV)) is soluble in dilute hydrochloric acid, while the precipitate from tetraoxosulphates (VI) is insoluble in dilute hydrochloric acid.
PERIOD 4: TETRAOXOSULPHATE (VI) ACID: – INDUSTRIAL PREPARATION, REACTIONS AND USES.
Tetraoxosulphate (VI) Acid is a chemical compound with the formula H2SO4.
INDUSTRIAL PREPARATION OF TETRAOXOSULPHATE (VI) ACID – H2SO4
The industrial or commercial production of H2SO4 is through a process known as the contact process. The process involves:
- The oxidation of sulphur (IV) oxide by air to sulphur (VI) oxide using a catalyst such as vanadium (V) oxide, V2O5.
SO2 is produced by burning sulphur or by burning pyrite, FeS2 in air.
S + O2 SO2
2SO2(g) + O2 2SO3(g)
- The absorption of sulphur (VI) oxide, SO3 in conc. H2SO4to form a fuming liquid called ‘Oleum’- heptaoxosulphate (VI) acid.
H2SO4(aq)+ SO3(g)→ H2S2O7(aq)– oleum
- The oleum is diluted with correct amount of water to produce the conc. H2SO4.
H2S2O7(aq)+ H2O(l)→ 2H2SO4(aq)
Note: a direct absorption of SO3 in water is not done – the reaction is violently exothermic, the heat evolved will cause the acid to boil producing a mist of fine drops of di H2SO4 which will fill the environment.
PROPERTIES OF H2SO4
- As an acid – H2SO4is dibasic and ionizes almost completely in solution, this makes it a strong acid. Due to it being dibasic, it forms two kinds of salts with alkalis.
2NaOH(aq)+ H2SO4(aq)→ Na2SO4(aq)+ 2H2O(l) and
NaOH(aq)+ H2SO4(aq)→ NaHSO4(aq)+ H2O(l)
- Action of dilute H2SO4on metals Reactive metals would displace hydrogen from dilute tetraoxosulphate(VI) acid.
Zn(s)+ H2SO4(aq)→ ZnSO4(aq)+ H2(g)
Note:* Less reactive metals such as copper will not displace hydrogen from dilute acid.* Cold concentrated H2SO4 is not attacked by any metal in the complete absence of water.
- Action on trioxocarbonate(IV) ,Carbon(IV) oxide is liberated when H2SO4is added onto a trioxocarbonate(IV).
Na2CO3(aq)+ H2SO4(aq)→ Na2SO4(aq)+ H2O(l)+ CO2(g) On a piece of marble, which has the chemical formula CaCO3, the reaction obtained is prematurely stopped due to the formation of the sparingly soluble salt, CaSO4, which forms a deposit on the surface of the marble.
- Conc. H2SO4as an oxidizing agent When hot and concentrated, the acid accepts electrons from reducing agents such as Cu or Zn. It also oxidizes non-metals, such as carbon and sulphur, and is reduced to SO2in the process.
S(s)+ 2H2SO4(aq)→ 2H2O(l)+ 3SO2(g)
C(s)+ 2H2SO4(aq)→ 2H2O(l)+ 2SO2(g)+ CO2(g)
The SO2 given off is detected using a strip of filter paper moistened with potassium heptaoxodichromate (VI) solution which turns orange to green – this is one of the tests for SO2 discussed earlier.
- As a dehydrating agent Tetraoxosulphate (VI) acid has a strong affinity for water. The addition of the acid to water (conc. acid should always be gradually added to water, with stirring of the liquid as the acid is added – to prevent the acid from forming a lower layer) produces a great amount of heat, hence the addition is not a physical change, but a chemical change.H2SO4is hygroscopic, that is, it absorbs water from the air and becomes dilute. When conc. H2SO4is added to many compounds, it decomposes them by removing elements water from them, that is, it dehydrates them. An example is the removal of rust from iron, and the dehydration of sugar. The sugar becomes a black mass of carbon. Dehydration is the removal of elements of water from a substance and the chemical composition of the substance is changed.
C12H22O11(s) + nH2SO4(l)→ 12C(s)+ 11H2O(l)+ nH2SO4(aq))
In a similar way, conc. H2SO4 acts on the skin and cloth.
TEST FOR TETRAOXOSULPHATE (VI) ION
The characteristic test for any soluble tetraoxosulphate(VI) is the formation of white precipitate (barium sulphate) when a solution of barium chloride, acidified with dilute HCl, or when a solution of barium trioxonitrate (v), acidified with dilute trioxonitrate (v) acid is reacted with it.
BaCl2(aq)+ Na2SO4(aq)→ 2NaCl(aq)+ BaSO4(s)
Ba(NO3)2(aq)+ Na2SO4(aq)→ 2NaNO3(aq)+ BaSO4(s)– white precipitate
Ionically, it represented thus
USES OF TETRAOXOSULPHATE (VI) ACID
Below are some of the uses of H2SO4
- for the manufacture of fertilizer, such as ammonium tetraoxosulphate (VI), (NH4)2SO4, and superphosphates.
- for the manufacture of paints and pigments.
- for the manufacture of artificial and natural fibre.
- for the manufacture of metallic tetraoxosulphate (VI), HCl, HNO3, HF, and plastics.
- for the manufacture of detergents, dyes, explosives and drugs.
- for the extraction of metals, example, in pickling (cleaning) iron and steel before plating them with tin or zinc.
- as electrolyte in lead-acid storage battery.
- In petroleum refining, where to is used to wash impurities out of gasoline and other refinery products
- If sulphur is dissolved in carbon(iv) sulphide and the solution is allowed to evaporate, the allotrope of sulphur formed is (a) plastic sulphur (b) amorphous sulphur (c) Rhombic sulphur (d) monoclinic sulphur (e) colloidal sulphur
- Sulphur is used for the following except. (a) Coating of steel to prevent rusting (b) vulcanization of rubber (c) prevention of growth of fungi (d) manufacture of dyes (e) manufacture of H2SO4acid
- Mono clinic and Rhombic are allotropes of (a) carbon (b) oxygen (c) Neon (d) Polonium (e) sulphur
- The crystalline allotrope of sulphur that is stable at room temperature is (a) plastic sulphur (b) amorphous sulphur (c) rhombic sulphur (d) colloidal sulphur (e) monoclinic sulphur
- Which of the following is the boiling point of sulphur (a) 115(b) 160 (c) 240 (d) 444 (e) 119
- State three properties of the element sulphur and outline three uses of sulphur
- Monoclinic sulphur and rhombic sulphur are the allotropes of sulphur, (i) what are allotropes (ii) name another element which has allotropes
- Describe what happens when sulphur is heated (i) in the absence of air (ii) in air and the product is dissolved in water. Give the equation of ll reactions involved.
- (a) What is the atomic number of sulphur (b) name four forms in which sulphur is found in nature?
- Briefly describe any three allotropes of sulphur (b) put down in tabular form the difference the main difference between rhombic sulphur and monoclinic sulphur.
Read New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio. Pages 381 -403
PRE READING ASSIGNMENT
Read up compounds of sulphur
Describe the stages in the manufacture of H2SO4 acid by contact process.
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