Question

${\text{KBr}}$, on reaction with ${\text{conc}}{\text{. }}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}$, gives reddish-brown gas which is:
A. Bromine
B. Mixture of bromine and
C. ${\text{HBr}}$
D. ${\text{N}}{{\text{O}}_2}$

Answer 1

Hint: KBr is an alkali metal halide. When it reacts with concentrated acid, we expect the halide to be liberated.

Complete step by step answer:
Potassium bromide on reaction with concentrated sulphuric acid gives potassium bisulphate, sulphur dioxide, bromine gas and water. The reaction for this can be given as –

& \text{ 2KBr + 3}{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}\text{ }\to \text{ 2KHS}{{\text{O}}_{4}}\text{ + B}{{\text{r}}_{2}}\text{ + S}{{\text{O}}_{2}}\text{ + 2}{{\text{H}}_{2}}\text{O} \\\ & \text{Potassium Sulphuric Potassium Bromine Sulphur Water } \\\ & \text{bromide acid bisulphate gas dioxide} \\\ \end{aligned}$$ Thus, the reddish-brown coloured gas we can see is of bromine. Bromine is a third lightest halogen and exists as a brownish liquid at room temperature but immediately vaporizes into fumes of the same colour. Additional information: All alkali metals are highly electropositive and halogens are highly electronegative in nature, all alkali metal halides are ionic in nature. Alkali metal halides are colourless crystalline solids and have very high melting and boiling points. Since, like dissolves like, all alkali metals are highly soluble in water. Elemental bromine does not occur freely in nature as it is highly reactive. It mostly exists in the form of mineral salts. Many compounds of bromine are known to have immense uses in our lives. Silver bromide along with silver iodide is mostly used in photographic emulsions. Ethylene bromide is used as an additive in fuel. Potassium bromide was earlier used as a sedative. Note: We may expect the reaction to produce $${{\text{K}}_2}{\text{S}}{{\text{O}}_4}{\text{ + 2HBr}}$$ instead of $${\text{KHS}}{{\text{O}}_4}$$, but that is not the case. Brown coloured gas is prominently of bromine and hence bromine has to be liberated free.