What is the mass fraction of sodium chloride NaCl in a solution obtained by dissolving 5 g of this salt in 45 g of water?

First of all, you need to find the mass of the solution.

The solution is composed of salt and water.

To do this, add up the available masses of salt and water.

M solution = M salt + M water = 5 + 45 = 50 grams;

The mass fraction of salt in the solution will be equal to the ratio of the mass of salt to the mass of the solution and will be equal to:

C salt = M salt / M solution = M salt / (M salt + M water) = 5 / (5 + 45) = 5/50 = 0.1 = 10%;