Calculate the percent by mass of 10 grams of calcium hydroxide mixed in 65 grams of water

13.3 %

Explanation:

Percent by mass indicates the mass of solute in 100g of solution.

We must know the solution's mass:

Solution's mass = Solute mass + solvent mass

Solution's mass = 10 g + 65 g = 75 g

Percent by mass = (10 g / 75 g).100 = 13.3 %

Otherwise, we can make a rule of three:

In 75 g of solution we have 10 g of solute

In 100 g of solution we must have (100. 10) / 75 = 13.3 %