Question

A solution is made by dissolving 40.0 g of KOH in 100 mL of water (density 0.995 g/mL) to form a solution. What is the mass percent solute in the solution?

1. 40.2%

2. 40.0%

3. 3.49%

4. 28.6%

5. 28.7%

Answer 1

Given mass of KOH is , m = 40.0 g

Volume of the water , V = 100 mL

Density of water , d = 0.995 g/mL

We know that density , d = mass/volume

So mass of water , W = volume x density

                                = 100 mL x 0.995 (g/mL)

                                = 99.5 g

So total mass of solution = mass of KOH + mass of water

                                     = 40.0 + 99.5 g

                                    = 139.5 g

So mass percent of KOH = ( mass of KOH / total mass of solution ) x 100

                                     = ( 40.0 / 139.5 ) x100

                                     = 28.7

Therefore the mass percent of the solute is 28.7 %

So option (5) is correct.