A piece of sodium hydroxide weighing 4.6 g was dipped into 100 ml of distilled water.

A piece of sodium hydroxide weighing 4.6 g was dipped into 100 ml of distilled water. Determine the mass fraction (%) of sodium hydroxide in the resulting solution.

First, let’s find the mass of water, which is included in the formula for finding the mass fraction of NaOH:

w = m (NaOH) / (m (NaOH) + m (H2O)).

The mass of water is equal to the product of volume and density (the density of water is 1 g / cm3 or 1 g / ml):

m = 100 * 1 = 100 g.

We find the mass fraction:

w = 4.6 / (4.6 + 100) = 0.04. As a percentage, the mass fraction of NaOH is 4%.