Acidic Properties of Tetraoxosulphate(VI) Acid

Sulphuric acid is the old name of tetraoxosulphate(VI) acid. It is a typical inorganic acid that reacts with bases, trioxocarbonates(IV) and metals. It is also a strong dibasic acid that undergoes ionization in water in two stages:

The formation of hydrogen tetraoxosulphate(VI) ion, HSO₄^-, and hydroxonium ion, H₃O⁺.

H₂SO₄(aq) + H₂O(l) → H₃O⁺(aq) + HSO₄^-(aq)

The hydrolysis of hydrogen tetraoxosulphate(VI) ion to hydroxonium ion and tetraoxosulphate(VI) ion.

HSO₄^- (aq) + H₂O(l) → H₃O⁺(aq) + SO₄^2-(aq)

The tetraoxosulphate(VI) acid reaction with metals depend on the position of the metal in the electrochemical series. Dilute tetraoxosulphate(VI) acid reacts with metals that are above hydrogen in the electrochemical series to liberate hydrogen gas, H_2, as the tetraoxosulphate(VI) salt of the metal is formed. This is exemplified by the reaction of metallic zinc with dilute tetraoxosulphate(VI) acid to form hydrogen gas and zinc(II) tetraoxolphate(VI) salt.

H₂SO₄(aq) + Zn(s) → ZnSO₄ + H₂(g)

Apart from the normal neutralization reaction where tetraoxosulphate(VI) acid reacts with alkali or bases to form salt and water, tetraoxosulphate(VI) acid also reacts with trioxocarbonate(IV) to liberate carbon(IV) oxide gas. An example is the reaction of copper(II) trioxocarbonate(IV) with tetraoxosulphate(VI) acid to form copper(II) tetraoxosulphate(VI) salt, water and carbon(IV) oxide gas.

H₂SO₄(aq) + CuCO₃(aq) → CuSO₄(aq) + H₂O(l) + CO₂(g)

The reaction can also be expressed ionically as,

2H⁺(aq) + CO₃^2-(aq) → H₂O(l) + CO₂(g)

Tetraoxosulphate(VI) acid enters into acid-base neutralisation reaction where the dilute acid reacts with bases or alkali to form salts and water. The dibasic nature of the acid allows it to form two types of salts. They are the acidic tetraoxosulphate salts as depicted by the formation of sodium hydrogen tetraoxosulphate(VI) salt in the presence of dilute tetraoxosulphate(VI) acid and limited sodium hydroxide

H₂SO₄(aq) + NaOH(aq) → NaHSO₄(aq) + H₂O(l),

and the normal sodium tetraoxosulphate(VI) salts as represented by the reaction of dilute tetraoxosulphate(VI) acid with excess sodium hydroxide:

H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l),

Another very important acidic reaction of tetraoxosulphate(VI) acid is the displacement of volatile acids from their salts. Examples of these salts include: trioxocarbonate(IV) salts, trioxonitrate(V) salts, Chlorides and by extension, trioxosulphate(IV) salts. These salts are of lower boiling points and as such distil over as vapours so that the reactions are used for the qualitative analysis of the metals in the salts.

Sodium hydrogen tetraoxosulphate(VI) salt and hydrogen trioxonitrate(V) gas are formed from sodium trioxonitrate(V) salt.

NaNO₃(s) + H₂SO₄(aq) → NaHSO₄(aq) + HNO₃(g)

Sodium hydrogen tetraoxosulphate(VI) salt is also formed from sodium trioxosulphate(IV), Na₂SO₃, salt with the elimination of sulphur(IV) oxide, SO₂, gas.

Na₂SO₃(s) + 2H₂SO₄(aq) → 2NaHSO₄(aq) + H₂O(l) + SO₂(g)

Carbon(IV) oxide gas is liberated with the formation of sodium tetraoxosulphate(VI) salt from sodium trioxocarbonate(IV) salt.

Na₂CO₃(s) + H₂SO₄(aq) → Na₂SO₄(aq) + H₂O(l) + CO₂(g)

Finally, potassium hydrogen tetraoxosulphate(VI) and hydrogen chloride gas are formed from potassium chloride.