A solution of NaOH has a concentration of 25.00% by mass. What mass of NaOH is present in 0.250 g of this solution? Use the periodic table in the toolbar if needed.

0.0625

g

What mass of NaOH must be added to the solution to increase the concentration to 30.00% by mass?

g

1) 0.0625 g.

2) 0.0125 g.

3) 80.0 g

Explanation:

edge

1) 0.0625 g.

2) 0.0125 g.

Explanation:

1) A solution of NaOH has a concentration of 25.00% by mass. What mass of NaOH is present in 0.250 g of this solution?

We can use the relation:

mass% of NaOH = [ (mass of NaOH) / (mass of solution) ] x 100.

mass% of NaOH = 25.0%, mass of NaOH = ? g, mass of solution = 0.250 g.

∴ mass of NaOH = (mass% of NaOH) (mass of solution) / 100 = (25.0%) (0.250 g) / 100 = 0.0625 g.

2) What mass of NaOH must be added to the solution to increase the concentration to 30.00% by mass?

We can use the relation:

mass% of NaOH = [ (mass of NaOH) / (mass of solution) ] x 100.

mass% of NaOH = 30.0%, mass of NaOH = ? g, mass of solution = 0.250 g.

∴ mass of NaOH = (mass% of NaOH) (mass of solution) / 100 = (30.0%) (0.250 g) / 100 = 0.075 g.

∴ The mass of NaOH should be added = 0.075 - 0.0625 = 0.0125 g.