Use quantities consistently
Practise moles, concentration and pressure.
The idea
Convert volumes to litres when computing molar concentration and use SI units for pressure. A pressure difference avoids adding atmospheric pressure.
A method to try
- Write the balanced chemical relationship or physical formula.
- Convert units before substituting.
- Check magnitude and units.
Follow the reasoning.
A solution contains 0.040 mol of solute in 250 mL. Calculate molar concentration.
- Convert 250 mL to 0.250 L before dividing. The total solution volume, rather than solvent volume alone, is the denominator.
- Concentration = 0.040/0.250 = 0.160 mol/L. Check by multiplying back: 0.160 mol/L × 0.250 L = 0.040 mol.
- That reverse check catches a common factor-of-one-thousand error from using millilitres as if they were litres. The amount, volume and concentration should be mutually consistent.
Think it through first.
How much does the pressure difference in the same still liquid change when depth doubles?
Show the explanation
It doubles.
For a fixed density and gravitational acceleration, the pressure difference ρgh is directly proportional to depth.
Make it your own
After reading, explain the method in your own words and identify the condition that makes it valid. Then try the linked starter practice without referring back to the worked example. Review the reasoning behind an error before repeating the same item; remembering an answer is different from being able to solve a new problem.
This lesson is one part of a short starter pathway. It does not cover the full exam syllabus or establish a predicted score.
Official references
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- MUR: 2026/27 decree DM 1005 (opens in a new tab)Checked 2026-09-20
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- University of Pavia: IMAT admission test (opens in a new tab)Checked 2026-09-20
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