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 170oC 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 96oC.
2 Monoclinic Sulphur: This is a needle like crystalline molecule consisting of S8. It has an amber colour and is stable at temperatures above 96oC. It easily reverts to Rhombic below 96oC. The transition temperature between Rhombic and Monoclinic is 96oC.
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 119oC and boils at 444oC
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 (S2-)
Fe(s) + S(s) → FeS(s)
2 It reacts with hydrogen to form hydrogen sulphide;
H2(g) + S(s) → H2S(g)
3. It reacts with excess oxygen to form sulphur (IV) oxide
O2(g) + S(s) →SO2(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) → FeCl2(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) + 3O2(g) → 2H2O(l) + 2SO2(g)
2H2S(g) + O2(g) → 2H2(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.
Na2SO3(aq)+2HCl(aq) → 2NaCl(aq)+ H2O(l) + SO2(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)+ SO2(g) → Na2SO3(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) + SO2(g) → 2H2O(l) + 3S(s)
C(s)+ SO2(g)→CO2(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 450oC and 1 atm pressure in the presence of vanadium (V) oxide or platinized asbestos as catalyst
2SO2(g) + O2(g) →2SO3(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.
Na2SO3(s)+2HCl(aq)→2NaCl(aq) + H2O(l) + SO2(g)
H2O(l)+ SO2(g) → H2SO3(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) + H2SO3(aq)→ Na2SO3(aq) + 2H2O(l)
2. It is oxidized in air to tetraoxosulphate (VI) acid
2H2SO3(aq) + O2(g) → 2H2SO4(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 SO32-
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) + O2(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 450oC to yield sulphur (VI) oxide.
SO2(g) + O2(g) → 2SO3(g) + heat
3. The sulphur (VI) oxide is then dissolved in concentrated H2SO4 to produce a thick oily liquid called Oleum.
H2SO4(aq) + SO3(g)→ H2S2O7(aq)
4. The Oleum is then combined with one mole of water to produce about 98% tetraoxosulphate (VI) acid.
H2O(l)+ H2S2O7(aq) 2H2SO4(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)+ H2SO4(aq)→ MgSO4(aq)+ H2(g)
ii. It reacts with bases to form salts and water ZnO(s)+H2SO4(aq) →ZnSO4(aq)+H2O(l)
iii. It reacts with alkali to form normal and acidic salt
H2SO4(aq)+KOH(aq)→NaHSO4(aq)+ H2O(l)
H2SO4(aq)+ KOH(aq)→ Na2 SO4(aq) + 2H2O(l)
iv.. It reacts with trioxocarbonate (IV) to liberate carbon (IV) oxide
H2SO4(aq)+CuCO3(aq)→CuSO4(aq)+ H2O(l) + CO2(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)+ 2H2SO4(aq)→ CuSO4(aq)+ 2H2O(l)+SO2(g)
C(s) + 2H2SO4(aq)→2H2O(l) + CO2(g)+ 2SO2(g)
H2SO4(aq)+ H2S(g)→S(s)+H2O(l)+ SO2(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
C12H22O11(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)+H2SO4(aq)→NaHSO4(aq) + HCl(g)
Test for SO42-
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
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