SS2 Chemistry Lesson Note on Tetraoxosulphate (VI) Acid

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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:

1. 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

2SO_2(g) + O₂    →  2SO_3(g)

2. The absorption of sulphur (VI) oxide, SO₃ in conc. H₂SO₄ to form a fuming liquid called ‘Oleum’- heptaoxosulphate (VI) acid.

H₂SO_4(aq)+ SO_3(g)→ H₂S₂O_7(aq)– oleum

3. The oleum is diluted with correct amount of water to produce the conc. H₂SO₄.

H₂S₂O_7(aq)+ H₂O_(l)→ 2H₂SO_4(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

1. As an acid – H₂SO₄ is 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)+ H₂SO_4(aq)→ Na₂SO_4(aq)+ 2H₂O_(l) and

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

2. Action of dilute H₂SO₄ on metals Reactive metals would displace hydrogen from dilute tetraoxosulphate(VI) acid.

Zn_(s)+ H₂SO_4(aq)→ ZnSO_4(aq)+ H_2(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.

3. Action on trioxocarbonate (IV), Carbon (IV) oxide is liberated when H₂SO₄ is added onto a trioxocarbonate (IV).

Na₂CO_3(aq)+ H₂SO_4(aq)→ Na₂SO_4(aq)+ H₂O_(l)+ CO_2(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.

4. Conc. H₂SO₄ as 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 SO₂ in the process.

S_(s)+ 2H₂SO_4(aq)→ 2H₂O_(l)+ 3SO_2(g)

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

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