Stop 9 of 12 · The path
Solutions — dissolved
Most chemistry happens in water. Solute dissolves in solvent; concentration says how crowded the solute is.
Bench tool
The molarity mixer
Molarity = moles ÷ litres. Push the numbers:
Concentration =
1 mol NaCl (58.5 g) in 1 L → 1 M. Halve the water → 2 M.
How it works
- Like dissolves like. Polar water takes salts and sugars; oil needs non-polar solvents.
- Stirring speeds, heating usually helps. Both move particles past each other faster.
- Dilution keeps moles. M₁V₁ = M₂V₂ — add water, moles stay.
Worked examples
0.5 L of 2 M sugar. 2 × 0.5 = 1 mol sugar inside.
Dilute 100 mL of 1 M to 0.25 M. Needs 400 mL total — add 300 mL water.
Oil and water. Shake all you like; they separate. Different polarities.
Where it goes wrong
Dissolving is not melting. Salt water still holds salt — evaporate to prove it.
Try it at home: sweet saturation
Fill the glass. Stir sugar into cold water spoon by spoon until one spoonful refuses to dissolve. Repeat with adult-poured warm water — the warm glass takes more. Solutions fill up, and warmth raises the limit.
For teachers
Learners say dissolved things vanish or melt — probe by asking how to get the salt back. Quickest check: ask what one extra crystal does in a saturated solution.