Question

Bromine turns starch iodide paper :
A. Blue
B. Red
C. Colourless
D. Yellow

Answer 1

Hint: Bromine is a more reactive halogen than iodine so, it can liberate iodine gas from potassium iodide. This iodine gas reacts with starch which acts as an indicator and gives a highly intense colour.

Complete Step by Step Answer:
Bromine reacts with potassium iodide to produce potassium bromide along with iodine gas as the products. The reaction can be given as follows:
$B{{r}_{2}}+2KI\to 2KBr+{{I}_{2}}$
Thus in this reaction one mole of bromine reacts with two moles of potassium iodide to form two moles of potassium bromide along with one mole of iodine gas. Thus in this reaction the iodide ion is oxidised to iodine gas. The liberated iodine can be used for further reactions.

Starch is a polymer of alpha D- glucose. It is a polysaccharide. Its monomer is glucose. Starch generally acts as an indicator in titration reactions to determine the end point of a titration. Iodine gas reacts with starch, an indicator gives blue colour. Thus we can write that bromine turns starch iodide paper blue.
Thus the correct option is A.

Note: If iodine liberate the bromine gas then it will give brown color as bromine is a brown colored gas. But it is not possible as bromine is more reactive.