redox

Question

Which of the following reaction would produce a halogen?
1) sodium chloride and concentrated sulphuric acid
2) sodium bromide and concentrarted sulphuric acid
3) sodium iodide and concentrated sulphuric acid

A. (1) only
B. (3) only
c. (1) and (2) only
d. (2) and (3) only

Answer 1

The answer is d.

(1) is incorrect.
Sodium chloride reacts with concentrated sulphuric acid to give hydrogen chloride gas and sodium hydrogensulphate.
NaCl + H2SO4 → NaHSO4 + HCl
The reducing power of hydrogen chloride is weak, and thus hydrogen chloride cannot be oxidized by the concentrated sulphuric acid.

(2) is correct.
Sodium bromide reacts with concentrated sulphuric acid to give hydrogen bromide gas and sodium hydrogensulphate. The reducing power of hydrogen bromide is quite strong, and thus hydrogen bromide formed is then oxidized by the concentrated sulphuric acid to give bromine.
NaBr + H2SO4 → NaHSO4 + HBr
2HBr + H2SO4 → 2H2O + SO2+ Br2

(3) is correct.
Sodium iodide reacts with concentrated sulphuric acid to give hydrogen iodide gas and sodium hydrogensulphate. The reducing power of hydrogen iodide is strong, and thus hydrogen iodide formed is then oxidized by the concentrated sulphuric acid to give iodine.
NaI + H2SO4 → NaHSO4 + HI
8HI + H2SO4 → H2S + 4H2O + 4I2