Grams in every 100 mL
Mass by volume percentage (% m/v).
A bottle of glucose
A hospital bottle is labelled 5 % glucose. Nobody weighs the whole liquid. They measure its volume in a jug.
Why measure volume, not mass?
What this lesson covers
The idea
Mass by volume percentage (% m/v) = (mass of solute ÷ volume of solution) × 100, the grams of solute in 100 mL of solution; it suits cases where measuring a liquid's volume is easier than weighing it.
A bottle of glucose
A hospital bottle is labelled 5 % glucose. Nobody weighs the whole liquid. They measure its volume in a jug.
Why measure volume, not mass?
- Measuring the volume of a liquid is easier than weighing it
- Liquids have no mass
- Volume cannot be measured
Make a glucose solution
Choose the volume and the grams of glucose. Make 5 % twice.
% m/v
Mass by volume percentage (% m/v or % w/v) = (mass of solute ÷ volume of solution) × 100. It tells how many grams of solute are in 100 mL of the solution. It is used where measuring the volume of a liquid is easier than weighing it, for example in medicines and laboratories.
Example 5.2. 5 g of glucose is dissolved in water to make 100 mL of solution. Percentage = (5 g ÷ 100 mL) × 100 = 5 % m/v.
Curiosity. A hospital saline drip is usually 0.9 % m/v sodium chloride: 0.9 g of salt in 100 mL of solution. It is safe for blood and replaces lost fluids.
Notes
% m/v = (mass of solute ÷ volume of solution) × 100: the grams of solute in 100 mL of solution.
Check yourself
10 g of glucose makes 200 mL of solution. What is the % m/v?
Answer: 5 % m/v
(10 g ÷ 200 mL) × 100 = 5 % m/v.
A saline drip is 0.9 % m/v. How many grams of salt are in 100 mL?
Answer: 0.9 g
0.9 g of salt in 100 mL.
Which unit goes with the solution in % m/v?
Where is % m/v commonly used?
- grams (mass). That is % m/m.
- millilitres (volume) — correct. Yes. % m/v is grams of solute per 100 mL of solution.
- litres per second. Not a unit of a solution’s amount.
- In medicines and laboratories, where volume is easier to measure — correct. Yes.
- Only for solid mixtures like spices. Spice mixtures use % m/m.
- Only to mix two liquids. That is % v/v.