Question

20 g salt is dissolved in water to prepare 20%
(w/w) aqueous salt solution. Calculate the amount
of salt added to this solution to make the final
concentration 30% (w/w). ​

Answer 1

Answer:

1Og

Explanation:

30(w/w),means 30g in 70g of solution.Therefore to make solution of 30 mass percentage 10g should be added to20mass percent solution.

Answer 2

Given:

20 g salt is dissolved in water to prepare 20%

(w/w) aqueous salt solution.

To find:

The amount of salt added to this solution to make the final concentration 30% (w/w).

Solution:

Concentration is given as-

The mass of the solute/mass of the solution is ×100.

The mass of the solute is 20 grams.

Let the mass of the solvent is x grams.

So, the mass of the solution is 20+x grams.

The concentration is 20%.

$\frac{20}{20 + x} \times 100 = 20 \\ 20 + x = 100 \\ x = 80$

Thus, the amount of solvent is 80 grams.

Let y amount of salt is added hence the new mass of solute is 20+y grams.

The mass of the solution is 80+20+y grams.

The concentration is 30%.

$\frac{20 + y}{100 + y} \times 100 = 30 \\ (20 + y) \times 10 = (100 + y) \times 3 \\ 200 + 10y = 300 + 3y \\ 100 = 7y \\ y = 14.28$

Thus 14.28 grams of salt should be added.