Define mass percentage and volume percentage. Find the mass percentage of a solution of 5 g of sugar in 45 g of water, and the volume percentage of 25 mL of ethanol in 200 mL of solution.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define mass percentage. Mass percentage = (mass of solute ÷ mass of solution) × 100, where mass of solution = solute + solvent.
2 · Define volume percentage. Volume percentage = (volume of solute ÷ volume of solution) × 100. Used for a liquid in a liquid.
3 · Work out the mass percentage.
Mass of solution = 5 + 45 = 50 g
(5 ÷ 50) × 100 = 10% w/w
4 · Work out the volume percentage.
(25 ÷ 200) × 100 = 12.5% v/v
5 · Real-life link. Product labels such as '70% v/v alcohol' on a hand sanitiser use volume percentage.
6 · Close in one line. Therefore the sugar solution is 10% w/w and the ethanol solution is 12.5% v/v.
Scoring tip: Write the formula before each sum and add mass of solute and solvent first. End with % w/w or % v/v.
