Sulphur

Quote of the Day “Outcome is not in your control. What is in your control is your effort and your intentions”- Professor Amit Sood

Objectives Sulphur Sulphur dioxide Reactions of sulphuric acid

Where is sulphur found? On the surface of the earth in volcanic areas. Extracted from natural gas and crude oil Underground deposits.

Uses of sulphur Used to make sulphuric acid and other chemicals Vulcanizing rubber Cosmetics, lotions, shampoos. Added to cement to make sulphur concrete.

Properties of sulphur Brittle yellow solid. Allotropes (Rhombic under < 96° C and monoclinic is> 96° C) Has a low melting point. Does not conduct electricity. Insoluble in water Reacts with metals to form sulphides. Burns in oxygen to from sulphur dioxide.

Rhombic and monoclinic sulphur

Sulphur Dioxide Heavy colourless gas with a choking smell. Has a boiling point of -10° C so can be easily liquiefied by pressuring it to 3 times atmospheric pressure.

Uses of sulphur dioxide Manufacture of sulphuric acid (Contact Process). Preservative for food and jam – stops the growth of bacteria and moulds. Used to make bleach, silk, wood pulp of making paper. Metal canisters of liquid sulphur dioxide are a convenient store for the gas. The compound is a liquid while it is under pressure in the canister. When the tap is opened and the pressure is released, the liquid boils and the gas forms.

Lab Preparation of Sulphur Dioxide Burning sulphur in air. Simplest way of making sulphur dioxide. A lot of sulphur dioxide for industry is made this way. Roasting sulphur-containing metal ores in air. This method is used in industry as a source of metal oxides and sulphur dioxide. The heating of iron pyrites is typical. 4 FeS2 (s) + 11 O2 (g) --------> 2 Fe2O3 (s) + 8 SO2 (g) The iron oxide formed is used to make iron. Action of acid on sulphite. Sulphur dioxide is made whenever sulphite salts are heated with dilute acid.

Lab Preparation of Sulphur Dioxide

Reactions of Sulphur Dioxide Sulphur dioxide is soluble in water. It turns damp blue litmus red. Sulphur dioxide reacts with alkalis. As soon as sulphur dioxide is bubbled through a solution of sodium hydroxide, the gas dissolves in the water of the solution and forms sulphurous acid.. This then neutralises the alkali, so that a salt plus water are formed. Sulphur dioxide is a strong reducing agent. This is only so when it is in solution. Change of colour as a test for sulphur dioxide. If bubbled through acidified potassium manganate (VII) solution, the potassium manganate is reduced. Purple to colourless. If bubbled through acidified potassium dichromate (VI) solution. It is reduced from orange to green.

Reactions of Sulphuric Acid Concentrated sulphuric acid is not an acid. This is because its structure is covalent. It does not contain hydrogen ions. When it is diluted its covalent structure breaks down and it ionises, evolving a great deal of heat. H2SO4 (l) ---------> 2 H+ (aq) + SO42- (aq) Remember when diluting concentrated sulphuric acid, add acid to water. The diluted solution may boil as the acid is being added. Once sulphuric acid is dilute, it adopts acidic characteristics. Hot concentrated sulphuric acid is an oxidising agent. It will oxidise metals to form salts, being reduced by the metals to form sulphur dioxide and water. Cu (s) + 2H2SO4 (l) --------> CuSO4 (aq) + SO2 (g) + 2 H2O (l)

Reactions of Sulphuric Acid Cold concentrated sulphuric acid is a dehydrating agent. When cold concentrated sulphuric acid is added to blue copper (II) sulphate crystals, they slowly turn white as their water of crystallisation is removed by the acid. CuSO4.5 H2O (s) --------> CuSO4 (s) + 5 H2O (g) Blue white 2. When cold concentrated sulphuric acid is added to sucrose, it goes black. Sucrose is a carbohydrate and when the water elements are removed from its molecules, only carbon is left. C12H22O11 --------------> 12 C + steam + decomposition products of the acid