Modern inorganic chemistry

GROUP VI 301

CuSO 4 .5H 2 O -» CuSO 4 + 5H 2 O

and also 'combined' water, for example in sugars and other organic

compounds:

C^H^On -» 12C + 11H 2 O

-» C0| + C0 2 | + H 20

HO O

ethanedioic acid

(oxalic acid)

Oxidising properties

Concentrated sulphuric acid is an oxidising agent, particularly

when hot, but the oxidising power of sulphuric acid decreases

rapidly with dilution. The hot concentrated acid will oxidise non-

metals, for example carbon, sulphur and phosphorous to give,

respectively, carbon dioxide, sulphur dioxide and phosphoric(V)

acid. It also oxidises many metals to give their sulphates; cast iron,

however, is not affected. The mechanisms of these reactions are

complex and the acid gives a number of reduction products.

Hot concentrated sulphuric acid is a useful reagent for differenti-

ating between chloride, bromide and iodide salts, since it is able to

oxidise (a) iodide, giving iodine (purple) and the reduction products,

hydrogen sulphide, sulphur and sulphur dioxide together with a

little hydrogen iodide; (b) bromide, giving bromine (red-brown) and

the reduction product sulphur dioxide together with hydrogen

bromide. It is unable to oxidise the chloride ion and steamy fumes of

hydrogen chloride are evolved.

Acidic properties

Concentrated sulphuric acid displaces more volatile acids from

their salts, for example hydrogen chloride from chlorides (see above)

and nitric acid from nitrates. The dilute acid is a good conductor

of electricity. It behaves as a strong dibasic acid :

H 2 SO 4 4- H 2 O ^ H 3 O+ + HSO4 : Ka = 40 mol T^1 at 298 K

HSO4 + H 2 O^H 3 O+ +SO5":Ka=1.0x 1(T^2 mol 1~^1 at 289K