Question

Solubility product of silver bromide is 5.0 x 10 -13. The quantity of potassium bromide (molar mass taken as 120 g of mol–1) to be added to 1 litre of 0.05 M solution of silver nitrate to start the precipitation of AgBr is

(1) 1.2 x 10–10 g

(2) 1.2 x 10–9 g

(3) 6.2 x 10–5 g

(4) 5.0 x 10–8 g

Answer 1

(2)

Ag+ + Br– ⇌ AgBr

Precipitation starts when ionic product just exceeds solubility product

i.e., precipitation just starts when 10–11 ***** of KBr is added to 1L of AgNO3 solution.

No. of ***** of KBr to be added = 10-11

weight of KBr to be added 10-11 x 120

= 1.2 x 10-9 g