Exploring Mixtures and their Separation
Concentration
Measure how concentrated a solution is.
The concentration of a solution tells you how much solute (the thing dissolved) is in a given amount of solvent or solution.
"Why does it matter?" Because the right amount decides whether something works or harms:
- Change the salt or sugar in ORS and it is no longer ORS.
- Too little pesticide doesn't work; too much harms the crops, the soil and the environment.
An Indian doctor who saved millions. Dilip Mahalanabis, a children's doctor, developed ORS (oral rehydration solution) to treat the dangerous loss of water caused by diarrhoea and cholera. The World Health Organization spread it worldwide, and it has saved millions of lives. Careful: not every sugary drink is ORS.
There are three ways to write concentration as a percentage. All of them are part ÷ whole × 100.
| Type | Formula | Example | Used for |
|---|---|---|---|
| Mass by mass (% m/m) | mass of solute ÷ mass of solution × 100 | 10 g salt + 90 g water = 100 g solution, so 10% | Packaged food, milk powder, spice mixes |
| Mass by volume (% m/v) | mass of solute ÷ volume of solution × 100 | 5 g glucose made up to 100 mL, so 5% | Medicines |
| Volume by volume (% v/v) | volume of solute ÷ volume of solution × 100 | 1 mL pesticide in 100 mL spray, so 1% | Two liquids that mix: perfumes, vinegar |
A real example: a hospital saline drip is 0.9% m/v salt. That means 0.9 g of salt in every 100 mL.
A small tip:
- Finding a percentage: multiply by 100.
- Using a given percentage: divide by 100.
In industry you may see % w/w; it is the same number as % m/m.
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