Determine the mass fraction of the soluble substance obtained by dissolving 10 grams of salt in 70 grams of water.

To solve the problem, we write down the given: m (salt) = 10 g, m (water) = 70 g
Find: mass fraction of soluble substance (w) -?
Decision:
Let’s write down the formula by which we will calculate the mass fraction:
w = m (substance) / m (solution)
To calculate the mass of the solution, it is necessary to add the mass of water to the mass of salt.
m (solution) = m (salt) + m (H2O)
m (solution) = 10 + 70 = 80 g
I know the mass of the salt and the mass of the solution, we can calculate the mass fraction. Let’s plug our data into the formula.
w = 10/80 = 0.125
Mass fraction is measured either in fractions of units or in percent. In order to convert the resulting number into percentages, multiply it by 100
Answer: w = 0.125 or 12.5%