A workstudy student is asked to prepare 100 mL NaOH solution

A work-study student is asked to prepare 100. mL NaOH solution with a concentration of 5.0% by mass. How many grams of NaOH should he use? Assume the density of 5% NaOH solution is previously reported as 1.02 g/mL.

Solution

volume of solution = 100 mL
density = 1.02 g/mL
so,
mass of solution = density * volume
= 1.02 g/mL * 100 mL
= 102 g

now use:
mass % = mass of NaOH * 100 / mass of solution
5 = mass of NaOH * 100 / 102
mass of NaOH = 5.10 g

Answer: 5.10 g