To 120 g of a 15% sodium hydroxide solution was added 11 g of sodium hydroxide.

To 120 g of a 15% sodium hydroxide solution was added 11 g of sodium hydroxide. Determine the mass fraction of NaOH in the resulting solution?

Given:

m (solution NaOH) = 120 g

m (NaOH) = 11 g

w% (NaOH) = 15%

To find:

w% (NaOH in final solution) -?

Decision:

1) Find the mass of sodium hydroxide in the initially given solution:

m (NaOH) = 120 g * 0.15 = 18 g;

2) Find the mass of the solution by adding a portion of sodium hydroxide:

m (NaOH solution) = 120 g + 11g = 131 g;

3) Find the mass of sodium hydroxide in the solution after adding alkali:

m (NaOH) = 18 g + 11 g = 29 g;

4) Find the mass fraction of alkali in the resulting solution:

w% (NaOH) = 29g: 131g * 100% = 22.1%.

Answer: w% (NaOH) = 22.1%.