Question

Calculate the amount of solute added to 150 mL
of 20% aqueous solution to make its concentration
30% (v/v).
9.​

Answer 1

initial concentration of aqueous solution is 20% (v/v).

(v/v) means, volume of solute in 100 ml of solution.

then, 20% (v/v) means , 20mL of solute is available 100ml of solution.

so, in 150ml solution, 20/100 × 150 = 30ml of solute will available.

Let's make it more clear,

initial amount of solute = 30ml

initial amount of solution = 150ml

Let's add x mL of solute in 150ml of solution.

then, concentration of solution (% v/V) = (30 + x)/(150 + x) × 100

given, final concentration is 30% .

so, 30% = (30 + x)/(150 + x) × 100

or, 0.3 = (30 + x)/(150 + x)

or, 0.3(150 + x) = 30 + x

or, 45 + 0.3x = 30 + x

or, 15 = 0.7x

or, x = 15/0.7 = 21.42ml