Question

Calculate the mass in grams of NaOH that must be added to make a 15% solution. Density of water= 1g/ml.

Answer 1

Mass percentage $(\frac{W}{W})$ is the mass of solute ( in grams) in $100g$ solution expressed in percentage

Mass by volume percentage $(\frac{W}{V})$ is the mass of solute present in $100ml$ of aqueous solution.

The $15\%$ solution of NaOH is not specified.

Assuming it is $15\%$ in reference to mass percentage $(\frac{W}{W});$

$15g$ of NaOH will be dissolved in $(100-15)=85g$ of water

Volume of $85g$ of water $=\frac{85}{1}=85ml$

Therefore $15g$ of NaOH will be dissolved in 85ml of water.

From mass by volume percentage concept;

$15g$ of NaOH will be dissolved to make 100ml of solution