ALKYNES

 

UNSATURATED HYDROCARBON (ALKYNES)

Alkynes are a homologous series of unsaturated hydrocarbons containing triple bond. It has a functional group of (≡) and general molecular formular of C_nH_2n-2 where n= 1,2,3, ... n for successive members of the group. 

The first member of the alkyne family is ethyne (acetylene).

 Alkynes are named by replacing ending –ane  of the corresponding alkane with –yne.

 

NOTE: Since alkynes contain triple bonds between C≡C therefore n=1 is not visible.

When n=	General Molecular Formulae  CnH2n-2	Name
2.	C2H2x2-2 = C2H2	Ethyne
3.	C3H2x3-2 = C3H4	Propyne
4.	C4H2x4-2 = C4H6	Butyne
5.	C5H2x5-2 = C5H8	Pentyne
6.	C6H2x6-2 = C6H10	Hexyne
7.	C7H2x7-2 = C7H12	Heptyne
8.	C8H2x8-2 = C8H14	Octyne
9.	C9H2x9-2 = C9H16	Nonyne
10.	C10H2x10-2 = C10H18	Decyne
11.	C11H2x11-2 = C11H20	Undacyne
12.	C12H2x12-2 = C12H22	Dodecyne
13.	C13H2x13-2 = C13H24	Tridecyne
14.	C14H2x14-2 = C14H26	Tetradecyne
15.	C15H2x15-2 = C15H28	Pentadecyne
16.	C16H2x16-2 = C16H30	Hexadecyne
17.	C17H2x17-2 = C17H32	Heptadecyne
18.	C18H2x18-2 = C18H34	Octadecyne
19.	C19H2x19-2 = C19H36	Nonadecyne
20.	C20H2x20-2 = C20H38	Icosyne/Eiocosyne
21.	C21H2x21-2 = C21H40	Heneicosyne
22.	C22H2x22-2 = C22H42	Docosyne
23.	C23H2x23-2 = C23H44	Tricosyne
24.	C24H2x24-2 = C24H46	Tetracosyne
25.	C25H2x25-2 = C25H48	Pentacosyne
26.	C26H2x26-2 = C26H50	Hexacosyne
27.	C27H2x27-2 = C27H52	Heptacosyne
28.	C28H2x28-2 = C28H54	Octacosyne
29.	C29H2x29-2 = C29H56	Nonacosyne
30.	C30H2x30-2 = C30H58	Triacontyne

 

 MOLECULAR STRUCTURES OF ALKYNES

N	ALKYNES	STRUCTURAL FORMULAR	MOLECULAR FORMULAR
2.	C2H2 Ethyne	H-C≡C-H	HC≡CH
3.	C3H4 Propyne	H  H-C-C≡C-H       H	CH3C≡CH
4.	C4H6 Butyne	H H  H-C-C-C≡C-H      H H	CH3CH2C≡CH
5.	C5H8 Pentyne	H H H  H-C-C-C-C≡C-H      H H H	CH3(CH2)2C≡CH
6.	C6H10 Hexyne	H H H H  H-C-C-C-C-C≡C-H      H H H H	CH3(CH2)3C≡CH
7.	C7H12 Heptyne	H H H H H  H-C-C-C-C-C-C≡C-H      H H H H H	CH3(CH2)4C≡CH
8.	C8H14 Octyne	H H H H H H  H-C-C-C-C-C-C-C≡C-H       H H H H H H	CH3(CH2)5C≡CH
9.	C9H16 Nonyne	H H H H H H H  H-C-C-C-C-C-C-C-C≡C-H      H H H H H H H	CH3(CH2)6C≡CH
10.	C10H18 Decyne	H H H H H H H H  H-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H	CH3(CH2)7C≡CH
11.	C11H20 Undecyne	H H H H H H H  H H  H-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H  H	CH3(CH2)8C≡CH
12.	C12H22 Dodecyne	H H H H H H H H HH  H-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H HH	CH3(CH2)9C≡CH
13.	C13H24 Tridecyne	H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H	CH3(CH2)10C≡CH
14.	C14H26 Tetradecyne	H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H H	CH3(CH2)11C≡CH
15.	C15H28 Pentadecyne	H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H HH H H H H H H H H H	CH3(CH2)12C≡CH
16.	C16H30 Hexadecyne	H H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H H H H	CH3(CH2)13C≡CH
17.	C17H32 Heptadecyne	H H H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H H H H H	CH3(CH2)14C≡CH
18.	C18H34 Octadecyne	H H H H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H      H H H H H H H H H H H H H H H H	CH3(CH2)15C≡CH
19.	C19H36 Nonadecyne	H H H H H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H H H H H H H	CH3(CH2)16C≡CH
20.	C20H28 Eiocosyne	H H H H H H H H H H H H H H H H H H  H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C≡C-H       H H H H H H H H H H H H H H H H H H	CH3(CH2)17C≡CH

NOMENCLATURE OF ALKYNES

The nomenclature of alkynes is similar to that of alkenes in many respects as shown in the structures below. The only difference lies on the type of bonds, in alkenes (double bond) and alkynes (triple bond).

 

(i)         CH₃-CH₂-C≡CCH₃                     (ii)        CH₃CH₂CH₂C≡CCH₃    

            Pent-2-yne                                           hex-2-yne

            CH₃                                                      CH₃

(iii)       CHC≡CCH₃                               (iv)       CH₂-C≡C-CH₂

CH₃                                                                        CH₃

             4-methylpent-2-yne                            hex-3-yne

                   CH₃                                                                   CH₃       CH₃

(v)        CH₃CHC≡CCHCH₃                                (vi)       CH₃C-C≡C-C-CH₃

                                CH₃                                           CH₃      CH₃

            2,5-dimethylhex-3-yne                                    2,2,5,5-tetramethylhex-3-yne

                                 CH₃

(vii)      CH₃CH-C ≡CC-CH₂CH₃                                 (viii)     CH₃C≡CCH₂

                   CH₃         CH₃                                                           CH₃

             2,5,5-trimethylhept-3-yne                              pent-2-yne

                      CH₃                                                                              CH₃ 

(ix)       CH≡CC-C=C-------CH—CH₂CH₂C≡CH               (x)        CH₃C-CHC≡CC≡CC≡CH 

                      CH₃              CH₂CH₃                                                    CH₂CH₃  

            6-ethyl,3,3-dimethyldec-1,6-diyne                 8-ethyl, 8-methynon-1,3,5-triyne

                                                                                              Cl

(xi)       CH₃C≡CCHCH₃                                    (xii)      CH₃-C-C≡CH 

                          Cl                                                                  Cl

            4-chloropent-2-yne                                         3,3-dichlorobut-1-yne

(xiii)     CH₃CHC≡CC≡CCHCH₃                          (xiv)     CH₃CHC≡CCHC≡CH  

                   Cl                Br                                                      Cl         Cl

            2-bromo, 7-chlorooct-3,5-diyne                     3,6-dichlorohept-1,3-diyne

                        H    

                    H-C-H      

             H H H           

(xv)  H-C-C-C-CC≡CH

             H H H        

                   H-C-H

                       H

            3,3-dimethylhex-1-yne

LABORATORY PREPARATION OF ETHYNES (ALKYNES)

Ethyne is prepared in the laboratory by adding cold water into calcium dicarbide (CaC₂). Much heat is evolved and sand is placed beneath the flask to protect the flask from breakage. Ethyne is collected over water. The chief impurity, phosphine, PH₃ is absorbed by the acidified CuSO₄ solution.

EQUATION FOR THE REACTION

CaC₂  +  2H₂O → Ca(OH)₂  +  C₂H₂.

                                                 Ethyne

 

 

PHYSICAL PROPERTIES OF ETHYNE

1. It is colourless gas

2. It has sweet smell when pure

3. Almost insoluble in water

4. It is neutral to litmus

5. It is strongly exothermic

CHEMICAL PROPERTIES OF ETHYNE

 Alkynes such as ethyne also undergoes addition reaction – a reaction in which one molecule of a compound is simply added on to the alkynes at the position of the carbon – carbon triple bond (C≡C) and this is converted to carbon – carbon single bond (C-C) that is, the alkanes. Examples of addition reaction are:

1.     Reaction of ethyne with hydrogen in the presence of nickel as a catalyst

                            Ni

            CH≡CH + 2H₂   →   CH₃CH₃   

            ethyne                           ethane

2. Reaction of ethyne with bromine to produce 1,1,2,2-tetrabromoethane. The reddish brown colour of bromine is destroyed.

            CH≡CH + 2Br₂ → CHBr₂-CHBr₂

3. Reaction of ethyne with chlorine to produce hydrogen chloride

            CH≡CH + Cl₂ → 2C+ 2HCl

4. Reaction of ethyne with oxygen or combustion reaction of ethyne (alkynes) to produce carbon(iv)oxide and water

            2CH≡CH + 5O₂  →4CO₂ + 2H₂O

5. Polymerization reaction of ethyne to produce benzene.

            3C₂H_{2 →} C₆H₆ 

6. Reaction of ethyne with water in the presence of dilute H₂SO₄ and mercury as a catalyst to produce ethanal

            CH≡CH + H₂O →CH₃CHO

7. Reaction of ethyne with KMnO₄ to produce 1,2-ethan-diol (glycol)

            CH≡CH  +KMnO₄ →CH₂-CH₂

                                                OH   OH

                                               1,2-ethan-diol

USE OF ETHYNE

1. In oxy-acetylene flame for welding and cutting of metals

2. In oxy-acetylene torch

3. In preparation of acetic acid

4. as a starting material for making polyvinylchloride (PVC) which is used in electrical insulation and water proofing.

TESTS TO DISTINGUISHED BETWEEN ALKANES, ALKENES AND ALKYNES.

The following test can be performed to distinguished clearly the different classes of hydrocarbons, that is, the alkanes, alkenes and alkynes.

All alkanes are saturated compounds while both alkenes and alkynes are unsaturated.

TEST 1: To the suspected hydrocarbons, add an acidified solution of KMnO₄ or K₂Cr­₂O₇ solution. Alkanes have no effect in any of these solutions while both alkenes and alkynes decolorized. Acidified KMnO₄ solution changes from purple to colourless, while K₂Cr₂O₇ changes from orange to green.

TEST 2: To the suspected hydrocarbons, add the solution of Ammonical copper (i) chloride. Alkanes and alkenes have no effect, but alkynes form a yellowish or reddish –brown precipitate.

2NH₄OH_(aq)+ 2CuCl  + C₂H₂ → CuC₂  + 2NH₄Cl  + 2H₂O.

TEST: To the suspected hydrocarbon, add solution of Ammonical silver tronitrate (v). Alkanes and alkenes have no effect, but alkynes form a yellowish precipitate.  

2NH₄OH + 2AgNO₃ + C₂H₂ → 2AgC + 2NH₄NO₃ + 2H₂O.

 

SULPHUR AND ITS COMPOUNDS at a glance

 

 SULPHUR

CONTENT

•             General Properties of Sulphur Group.

•             Electronic Structure of Sulphur Group.

•             Extraction of Sulphur.

•             Allotropes of Sulphur.

•             Uses of Sulphur

GENERAL PROPERTIES OF GROUP VI ELEMENTS

Group VI elements include Oxygen, Sulphur, Selenium, Tellurium and Polonium.  

1.   All the elements are solid except oxygen which is a gas at room temperature

2.  Metallic property increases down the group. Oxygen and sulphur are non-metal; selenium and tellurium are metalloid, while polonium is a metal.

3. Oxygen and sulphur exhibit allotropy.

4.   They have six electrons in their outermost shell. Hence their oxidation number is -2; though sulphur can exhibit -4 and -6 states in some compounds.

5.  Electronegativity decreases down the group. Thus, oxygen is a good oxidizing agent.

ELECTRONIC STRUCRURE OF SULPHUR GROUP

 The electronic configurations of the members of the group are shown below: 

Oxygen = 8: - 1s² 2s² 2p⁴

Sulphur = 16: - 1s² 2s² 2p⁶ 3s² 3p⁴

Selenium= 34: - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

Tellurium = 52: - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁴

Polonium = 84: - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁴

SULPHUR

Sulphur is found in group VI period II in the Periodic Table. It occurs as a free element found in underground deposits. It is also  found in the combined state as metallic  Sulphide and as tetraoxosulphate (IV).

EXTRACTION OF SULPHUR

Sulphur is extracted from underground deposits by the Frasch process. In this process: Three concentric pipes are is driven down a hole drilled to the Sulphur bed.  Super  heated water at 170^oC and 10atm is forced down one of the pipes to melt the solid Sulphur, hot compressed air is then forced down the second pipe as a result the molten Sulphur is then forced out through the third pipe by the compressed air. The molten Sulphur is continuously pumped out into large tanks where it is allowed to solidify. Sulphur obtained is  about 99.5% pure.

ALLOTROPES OF SULPHUR

There are two main crystalline allotropes of Sulphur they are: -

1   Rhombic Sulphur: This is a bright yellow octahedral crystalline solid made up of S₈ molecules. It is stable below 96^oC.

2 Monoclinic Sulphur: This is a needle like crystalline molecule consisting of S8. It has an amber colour and is stable  at temperatures above 96^oC. It easily reverts to Rhombic below 96^oC. The transition temperature between Rhombic and Monoclinic is 96^oC.

Comparison of the Physical Properties of Rhombic and Monoclinic Sulphur

	Rhombic sulphur	Monoclinic sulphur
Colour	Bright yellow	Amber
Shape	Octahedral	Needle-shaped
Density	2.80 g/cm3	1.98g/cm3
Melting point	1130C	119oC
Stability	Stable below 96oC	Stable above 96oC

There are other non crysatlline allotropes of Sulphur such as 

1.  Amorphous sulphur: formed when sulphur is dissolved in carbon(IV) sulphide and the solution is allowed to evaporate.

2.  Plastic sulphur: formed when molten Sulphur is suddenly poured into cold water:00

     

PHYSICAL PROPERTIES

1.   Sulphur is a yellow solid.

2.    It melts at 119^oC and boils at 444^oC

3.   It is insoluble in water but soluble in carbon (IV) sulphide and tolune

3.    It is a poor – conductor of heat and electricity.

CHEMICAL PROPERTIES

1.  It reacts directly with metals to form sulphide (S^2-)

   Fe_(s) + S_(s) → FeS_(s)

2    It reacts with hydrogen to form hydrogen sulphide;

       H_2(g) + S_(s) → H₂S_(g)

 3.   It reacts with excess oxygen to form sulphur (IV) oxide

  O_2(g) + S_(s) →SO_2(g)

 4.  It reacts with coke (carbon) to form carbon (II) sulphide 

     C(s) + S(s) → CS₂   

USES

1.  It used in manufacturing tetraoxosulphate (IV) acid

2.  It used in vulcanization of rubber

3.   It used as germicides

4.   It used in manufacturing bleaching agent

COMPOUNDS OF SULPHUR

1.    HYDROGEN SULPHIDE, H2S

Hydrogen sulphide is found in volcanic gases, sulphur springs, coal gas and natural gas.

LABORATORY PREPARATION

Hydrogen sulphide is prepared in the laboratory by the action of dilute acids on metallic sulphide like Iron (II) sulphide 

2HCl_(aq)+ FeS_(s) → FeCl_2(aq) + H₂S_(g)

The apparatus used for regular supply of hydrogen sulphide in the laboratory is Kipp’s apparatus.

                 

PHYSICAL PROPERTIES

1.  Hydrogen sulphide is a colourless gas

2. It smells  like that of rotten egg.

2.  It is a poisonous gas 

3.  It is about 1.18 times denser than air.

4.  It is moderately soluble in water to form very weak acidic solution.

5.  It burns with pale blue flame.

CHEMICAL PROPERTIES

1. As an acid it reacts with alkali to form a normal salt and water    

   2NaOH_(aq) + H₂S_(g) → Na₂S_(aq) +2H₂O_(l)

2. It reacts with excess oxygen to form sulphur (VI) oxide but forms deposit of sulphur with limited oxygen

 2H₂S_(g) + 3O_2(g) → 2H₂O_(l) + 2SO_2(g)

 2H₂S_(g) + O_2(g) → 2H_2(l) + 2S_(s)

3.   As a reducing agent, it reacts with many oxidizing agents such as acidified KMnO₄, acidified K₂Cr₂O₇, chlorine gas, FeCl₂, SO₂, H₂SO₄ and HNO₃

TEST FOR HYDROGEN SULPHIDE

Moistened a piece of filter paper with lead (II) trioxonitrate (V) solution and dropped it into a gas jar of the unknown gas. If the paper turns black, then the gas is H₂S.

SULPHUR (IV) OXIDE, SO₂

LABORATORY PREPARATION

Sulphur (IV) oxide is prepared in the laboratory by heating sodium or potassium trioxosulphate (IV) with tetraoxosulphate (VI) acid or hydrochloric acid.

         Na₂SO_3(aq)+2HCl_(aq) →   2NaCl_(aq)+ H₂O(l) + SO_2(g)

Physical Properties 

1.            Sulphur (IV) oxide is a colourless poisonous gas.

2.            It smell like that of burning matches.

2. It is very soluble in water.

3.  It is about 2.5 times denser than air.

Chemical Properties

1.  As an acid: - it reacts with alkali to form normal salt and water only.

    2NaOH_(aq)+ SO_2(g) → Na₂SO_3(aq) + H₂O_(l)

2.   As reducing agent: - Sulphur (IV) oxide reduces oxidizing agents such as acidified KMnO₄; acidified K₂Cr₂O₇; FeCl₃, HNO₃, chlorine gas. It decolorizes acidified purple KMnO₄ and turns acidified orange K₂Cr₂O₇ to green.

3.   As an oxidizing agent: -Sulphur (IV) oxide reacts as oxidizing agent in the presence of strong reducing agent such as hydrogen sulphide.

2H₂S_(g) + SO_2(g) → 2H₂O_(l) + 3S_(s)

C_(s)+ SO_2(g)→CO_2(g)+ S_(s)

4.  As a bleaching agent: - It reacts as bleaching agent decolourising dye by its bleaching action. The bleaching action is similar to that of chlorine in that there must be water. But, while chlorine bleaches by oxidation sulphur IV oxide bleaches by reduction.

USES

1.It is used in manufacture of tetraoxosulphate (VI) acid.

2. It is used as a germicide and a fumigant especially for destroying termites.

3.  It is used as bleaching agent for straw, silt and wood.

4. It is used as preservative in some liquid e.g orange juice.

5.  Liquid sulphur (IV) oxide is used as refrigerant.

Test for SO2

1. Bubbled the unknown gas through solution of either acidified potassium heptaoxodichromate (VI) or potassium tetraoxomanganate (VII). If it changes the colour of acidified K₂Cr₂O₇ from orange to green or it changes the colour of acidified KMnO₄ purple to colourless, then the gas is SO₂ 

SULPHUR (VI) OXIDE, SO₃

Sulphur (VI) oxide is prepared by reacting sulphur (IV) oxide and oxygen at 450^oC and 1 atm pressure in the presence of vanadium (V) oxide  or platinized asbestos as catalyst

     2SO_2(g) + O_2(g) →2SO_3(g)

PHYSICAL PROPERTIES OF SO₃

1.  It is a white needle-like crystal at room temperature.

2.    It has a low boiling point and vapourizes on gentle heating.

3 It dissolves readily in water to give tetraoxosulphate (VI) acid.

TRIOXOSULPHATE IV ACID, H₂SO₃

Trioxosulphate (IV) acid is a dibasic acid with a molecular formula H₂SO₃

Laboratory Prepaaration  OF H₂SO₃

It is prepared in the lab by the action of dilute hydrochloric acid on heated sodium trioxosulphate (IV) to produce sulphur (IV) oxide, which is then dissolved in water.

    Na₂SO_3(s)+2HCl_(aq)→2NaCl_(aq) + H₂O_(l) + SO_2(g)

    H₂O_(l)+ SO_2(g) → H₂SO_3(aq)

Sulphur (IV) Oxide is the acid anhydride of trioxosulphate (IV) acid.

PHYSICAL PROPERTIES OF H₂SO₃

1. It is colourless liquid.

2.  It is readily soluble in water.

3. It has an irritating and choking smell.

Chemical Properties oF H₂SO₃

1. It reacts with alkalis to form salt and water.

     2NaOH_(aq) + H₂SO_3(aq)→ Na₂SO_3(aq) + 2H₂O_(l)

2.     It is oxidized in air to tetraoxosulphate (VI) acid

 2H₂SO_3(aq) + O_2(g) → 2H₂SO_4(aq)

3.    As a reducing agent: - It reduces oxidizing agent such as acidified KMnO₄ and acidified K₂Cr₂O₇

4    It bleaches dyes in the presence of water.

Test for SO₃^2-

Add a little amount of barium chloride solution to a solution of the unknown substance. If a white precipitate is formed which is soluble in dilute hydrochloric acid then the presence of a trioxosulphate (IV) ion is confirmed.

USES OF H₂SO₃

1.   It is used for bleaching straw and other fabrics.

2.  It is used as a germicide.

TETRAOXOSULPHATE VI ACID, H₂SO₄

Tetraoxosulphate VI acid is one of the most important chemical compounds known. It is used in almost every manufacturing process; hence it is mostly prepared industrially.

INDUSTRIAL PREPARATION OF H₂SO₄

It is manufactured industrially by Contact process. The following equations summarizes the steps involved in the Contact process.

1.   Sulphur is burnt in dry air to obtain sulphur (IV) oxide, SO₂

    S_(s) + O_2(g) → SO₂(g)

2.The Sulphur (IV) oxide produced is combined with excess oxygen in the presence of vanadium V oxide (V₂O₅ ) as catalyst at a temperature of 450^oC to yield sulphur (VI) oxide.

 SO₂(g) + O_2(g) → 2SO_3(g) + heat

3. The sulphur (VI) oxide is then dissolved in concentrated H₂SO₄ to produce a thick oily liquid called Oleum.

H₂SO_4(aq) + SO_3(g)→ H₂S₂O_7(aq)

4.    The Oleum is then combined with one mole of water to produce about 98% tetraoxosulphate (VI) acid.

 H₂O_(l)+ H₂S₂O_7(aq)  2H₂SO_4(aq)

NOTE: Dissolving Sulphur (VI) oxide in water directly is highly exothermic and will cause the acid to vaporize, producing a mist of droplets of the concentrated acid which can spread and cause acid burns.

PHYSICAL PROPERTIES

1.  It is a colourless, viscous liquid with density of 1.84gcm^-3

2.  It is corrosive and cause burns when in contact with the skin.

3. It is highly soluble in water evolving large amount of heat.

CHEMICAL PROEPERTIES

1.  As an acid, 

i.  It reacts with metal higher than hydrogen in the electrochemical series to liberate hydrogen ga Mg_(s)+ H₂SO_4(aq)→ MgSO_4(aq)+ H_2(g)

ii.  It reacts with bases to form salts and water ZnO_(s)+H₂SO_4(aq) →ZnSO_4(aq)+H₂O_(l)

iii.  It reacts with alkali to form normal and acidic salt

H₂SO_4(aq)+KOH_(aq)→NaHSO_4(aq)+ H₂O_(l)

 H₂SO_4(aq)+ KOH_(aq)→ Na₂ SO_4(aq) + 2H₂O_(l)

iv.. It reacts with trioxocarbonate (IV) to liberate carbon (IV) oxide

H₂SO_4(aq)+CuCO_3(aq)→CuSO_4(aq)+ H₂O_(l) + CO_2(g)

2.  As oxidizing agent: - Concentrated H₂SO₄ oxidize metals and non –metals to yield the corresponding tetraoxosulphate VI and itself reduced to SO2.  It oxidises hydrogen sulphide to Sulphur.

 Cu_(s)+ 2H₂SO_4(aq)→ CuSO_4(aq)+ 2H₂O_(l)+SO_2(g)

C_(s) + 2H₂SO_4(aq)→2H₂O_(l) + CO_2(g)+ 2SO_2(g)

H₂SO_4(aq)+ H₂S_(g)→S_(s)+H₂O_(l)+ SO_2(g)

3. As a dehydrating agent: - Concentrated tetraoxosulphate (VI) acid also behaves as a dehydrating agent, removing components of water from compounds like sugar and ethanedioic acid

         C₁₂H₂₂O_11(s)→12C_(s) +11H₂O_(l)

  ^{sugar                    charcoal}

  COOH

 |            + conc.                        COOH    H2SO4 → CO2 + CO + H2O            

 4.  Concentrated tetraoxosulphate (VI) displaces volatile acids from their salts 

 NaCl_(s)+H₂SO_4(aq)→NaHSO_4(aq) + HCl_(g)

Test for SO₄^2-

 Add Barium chloride solution to a solution of the unknown salt. If a white precipitate is formed which is insoluble in excess dilute hydrochloric acid, then the presence of a tetraoxosulphate (VI) ion is confirmed.

USES OF H₂SO₄

1.     It is used as an electrolyte in lead  accumulator.               

2.   It is used in production of fertilizers e.g ammonium tetraoxosulphate (VI).

3. It is used in purification of crude oil.

 4.  It is used as drying agent for many gases except NH₃ and H₂S gas.

5    It is used to clean metals before electroplating.

6.   It is used in the production of fibres

7.  It is used in the manufacture of synthetic detergents

TETRAOXOSULPHATE (VI) SALTS: - These are salts formed when metals, bases/ alkalis and trioxocarbonate IV reacts with H2SO4

USES OF TETRAOXOSULPHATE (VI) SALTS

1.  Ammonium tetraoxosulphate (VI) (NH4)2SO4 used as fertilizers

2.  Sodium tetraoxosulphate (VI) (Na2SO4) is used in paper manufacture and as a purgative

3.  Calcium tetraoxosulphate (VI) (CaSO4) is mined as gypsum and when heated forms plaster of Paris       (POP) used to set broken bones.

4. Aluminum tetraoxosulphate (VI) (Al2(SO4)3) is used to coagulate precipitate in purification of water

5. Iron II tetraoxosulphate (VI) is used to treat anemia.

OBJECTIVE QUESTIONS 

1. The acid anhydride of tetraoxosulphate (VI) acid is 

a. SO2 

b. SO3 

c. SO4 

d. SO

2. Which of the following compounds gives a white precipitate with acidified barium chloride solution? a. K2SO4 

b. NaNO3 

c. KCl 

d. CaCO3

3

4. Which of the following is used as catalyst in the Contact process? 

a. V2O5 

b. Platinum 

c. Fe3O2 

d. Nickel

5.Whatbis the effect of using vanadium  (V) oxide as a catalyst in the reaction represented by the following equation?  2SO2  + O2   SO3   H= -xkjmol-1 

A. Decreases the value of H

B. Increases the collision rate of reactant particles 

C. Shift equilibrium position to the right.

D. Reduces the time for attainment of equilibrium.

6. What is the colour of tetraoxosulphate VI acid?

 a. Colourless 

b. White 

c. Blue 

d. Pale white

7. In which of the following is the oxidation number of Sulphur equal to -2

A. S8

B. H2S

C.SO2

D.SO32-

8. 

9.            

10. Why do we acidify the solution used for testing for the presence of S042-

a. To prevent the precipitation of any other ion that may be present in the solution. 

b. To acidify the test solution. 

c. To increase the rate of the reaction 

d. The acid acts as catalyst.

THEORY QUESTIONS 

1.

(I). Name the process represented by the chart 

ii). Identify reactant X and product Y.

iii). What are the operating temperature and pressure at stage II

iv). Mention the stage which requires a catalyst and state the catalyst used. 

v) give the reason why the SO3 produced in stage II is not dissolved directly in water.

2.(a). State two physical properties of hydrogen sulphide 

(ii). Name the laboratory equipment used for intermittent production of hydrogen sulphide?

b. What property of hydrogen sulphide is illustrated in the reaction represented by the following equation? 

H2S + 2NaOH ---> Na2S + H2O 

EQUILLIBRIUM at a glance

EQUILLIBRIUM is said to be established in a reversible reaction when the rate of forward reaction is equally to the rate of backward reaction.

 We can describe equilibrium here as a state where there is no observable change.

In this Chapter we will be looking at Equilibrium in Chemistry and try to explain it as best as we can

Types of Equilibrium

Equilibrium can be Static  and  Dynamic

I. Static equilibrium: - In static equilibrium there is basically no movement within the system and the substances involved are at the same level. An example of a static equilibrium is when two children on a seesaw are suspended in space.

You will observe that both children suspended in space have the same potential energy. But any slight disturbance and the equilibrium will be lost.

Ii. Dynamic equilibrium: - In dynamic equilibrium, there is actually movements, but the changes are not observable. For example, a child going up an escalator that is actually descending at the same speed as the child, the child would seem to remain at a particular spot even though he is moving up.

Dynamic equilibrium can be grouped into two

I. Physical equilibrium and 

Ii. Chemical equilibrium

I. Dynamic physical equilibrium: -In dynamic equilibrium no new substance is formed (just like a physical change). For example, when sodium chloride is dissolved in water to give a saturated solution, the dissolved crystals will crystallize out of the solution just as undissolved crystals are dissolving into the solution, with these forward and backward reactions occurring at the same rate, we say the saturated solution is in equilibrium. 

NaCl(s) ⇌ NaCl(aq)

II. Dynamic Chemical Equilibrium: - In this equilibrium system a new substance is formed (just like a chemical change).

An example is the reaction between Nitrogen and Hydrogen to yield Ammonia

N2(g) + 3H2(g) ⇌ 2NH3(g)

In dynamic equilibrium a new substance is formed.

Properties Of a System in Equilibrium

If a system is in equilibrium, then it will possess the following properties

I. The reaction must be a reversible reaction 

Ii. The rate of forward reaction must be equal to the rate of backward reaction 

III. ∆G must be equal to zero. (delta G is the Gibbs free energy)

IV. The equilibrium can be approached from either side of the reaction.

V. The reaction must occur in a closed system.

Factors affecting a system in equilibrium position of a reversible reaction

I. Temperature 

II. Concentration 

III. Pressure

IV. Catalyst

 

Le Chatelier's Principle: See laws and principles

The effect in equilibrium position brought about by a change in any of the factors mentioned above was predicted and may be explained by Le Chatelier's principle 

i. How Temperature Affects equilibrium position of a reversible reaction: - Given a reaction where the forward reaction is exothermic, then the backward reaction will be endothermic.  For such a reaction, an increase in temperature will shift the position of Equilibrium to the left, that is, it will favor the backward reaction on the other hand, a decrease in temperature will favor the forward reaction since it does not require much heat.

How Concentration Affects the equilibrium position of a reversible reaction: - When any one of the reactants in a reversible reaction is increased this will cause the equilibrium position to shift to the right, favouring the forward reaction.   This is because an equilibrium has already been established and adding more reactants will alter that equilibrium, and so according to Le Chatelier's principle the reactants will be quickly used up and be converted to product. 

If the products are removed from the system as they produced, this can also cause the equilibrium to shift to the right.

For example, let us consider the equilibrium reaction of the Haber process, that the reaction between H2 and N2 the produce NH3 

 

                    N2(g) + 3H2(g) ⇌ 2NH3(g) 

An increase in the concentration of the N2 or H2 will cause the equilibrium position to shift to the right, favouring the forward reaction.

How Pressure Affects the equilibrium position of a reversible reaction: - For Pressure to affect the equilibrium position of a reversible reaction, at least one of the reactants or products must be a gas and the total number of mols (vol.) of the reactants must be different from the total number of mols (vol.) of the product. 

For example, considering the two reactions 

  1. Fe(s) + 4H2O(g) ⇌ Fe2O3 + 4H2(g) 

                  4vol.                      4vol.

      

         2.  N2O4(g) ⇌ 2NO2(g)

              1vol.        2vol.

Pressure cannot affect the position of equilibrium of equation 1 because the volumes of both the gaseous reactant and gaseous product are the same (i.e. 4vol.)

However, in equation 2. the total volume of reactants is different from the volume of product, so an increase in pressure for such a reaction will lead to a decrease in volume (Boyle's law) hence causing the equilibrium to shift the left (the position that has a small volume) favouring the backward reaction. Similarly, a decrease in pressure will result to an increase volume and this will cause the equilibrium to shift to the right (area with larger volume) favouring the forward reaction.

Equilibrium Constant 

The equilibrium constant for a reaction in equilibrium, is the product of the molar concentrations (or pressures) of the products divided by the product of the reactants raised to the power of the coefficient of each reactant.

For a reaction 

            aA +bB ⇌ cC + dD

The equilibrium constant for the reaction will be 

                Kc = [C]^c[D]^d
                        [A]^a[B]^b

         

OBJECTIVE QUESTIONS

1. what will happen if more heat is applied to the following system in equilibrium

   

     X_2(g) + 3Y_2(g) ⇌ 2XY_3(g); ∆H= -xkjmol^-1

   

A. The yield of XY₃ will increase.

B. More of will XY₃ decompose 

C. more of X₂ will react 

D. The forward reaction will go to completion

2. What is the expression for the equilibrium constant (Kc) for the following reaction?  N_2(g) + O_2(g) ⇌ 2NO_(g)

A.      [NO]²
      [N₂] + [O₂]  

 

b.       [2NO]²
         [N₂]]O₂]

 

c.     [N2] + [O]
          2[NO]²

 

d.       [NO]²

        [N₂][O₂]

3. A reaction represented by the equation below  

     A_2(g) + B_(2(g) ⇌ 2AB_(g); ∆H = +X kjmol^-1             

which of the following statement about the system is correct

a. The forward reaction is exothermic 

b. The reaction goes to completion at equilibrium 

c. Pressure has no effect on the equilibrium mixture

d. At equilibrium increase in temperature favours the reverse reaction.

 

4. What will happen if more heat is applied to the following system at equilibrium?

                X_2(g) + 3Y_(2(g) ⇌ 2XY_(g); ∆H = -X kjmol^-1

a). The yield will increase of XY³ will increase.

b).  More of XY₃ will decompose 

c). . More of X₂ will react 

d).  The forward reaction will go to completion

5. The position of equilibrium ina reversible reaction is affected by 

a). Particle size of the reactants 

b). Change in concentration of the reactants 

c). Change in the size of the reaction vessel 

d). Vigorous stirring of the reaction mixture.

THEORY

1(a). When few drops of aqueous KSCN are added to a solution of iron (III) salt the following equilibrium is s_{The equilibrium mixture has a pale colour}

                                          ^{Yellow      colourless         deep red} 

(i). Explain what will happen if more KSCN were added to the equilibrium mixture 

(ii). Which of the ions in the equilibrium mixture forms an insoluble hydroxide with NAOH (aq)?   Write an equation for the reaction

(iii).  State two changes observed on adding NaOH to the equilibrium mixture.

(b)i.