Question

What is the molarity of a 15 ml, 2 M aqueous solution when 285 ml of water is added to it?

(a) 0.400 M

(b) 0.100 M

(c) 0.111 M

(d) 0.105 M

I have been asked this question in examination.

My query is from Expressing Concentration of Solutions topic in section Solutions of Chemistry – Class 12

Answer 1

Right option is (b) 0.100 M

For explanation: Given,

Initial concentration, M1 = 2 M

Initial total volume, V1 = 15 ml

Final total volume, V2 = 15 + 285 = 300 ml

Final concentration, M2 = to be found

Before and after adding water number of moles of solute remain constant since it does not react with water.

Number of moles = concentration x volume

Thus, M1 x V1 = M2 x V2

On substituting, M2 = (2 x 15)/300 = 0.1 M.