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Concentration = mass of solute ÷ volume of solution in g/dm³, so mass of solute = concentration × volume. Free notes and 8 questions answered.
Calculating Mass of Solute in Solutions is part of Use of amount of substance in relation to masses of pure substances in GCSE AQA Higher Chemistry.
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Concentration = mass of solute ÷ volume of solution in g/dm³, so mass of solute = concentration × volume. Free notes and 8 questions answered.
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Use this lesson to stay inside Use of amount of substance in relation to masses of pure substances while connecting the detail back to the wider Topic 3: Quantitative chemistry topic.
Read the core explanations from Calculating Mass of Solute in Solutions before testing yourself from memory.
When you dissolve sugar in tea, you create a solution. But how much sugar is actually in there? This is where concentration becomes crucial - it tells us exactly how much solute is packed into each unit of solution.
Think of concentration like the strength of your coffee. More coffee grounds (solute) in the same amount of water (solvent) gives you a stronger, more concentrated drink. In chemistry, we measure this precisely using mass per unit volume.
Every concentration calculation uses the same fundamental relationship. Once you master this formula, you can find any missing piece of the puzzle.
This formula can be rearranged to find any unknown value. If you know concentration and volume, you can find the mass of solute - which is exactly what we need for exam questions.
Here's where students often lose marks. Concentration can be given in g/dm³ or g/cm³, and volume in dm³ or cm³. The units must match, or your answer will be wrong by a factor of 1000.
Let's tackle some exam-style questions. These follow the exact format you'll see in your GCSE, complete with mark schemes.
Worked example: Calculating Mass of Solute
A solution has a concentration of 25 g/dm³. Calculate the mass of solute in 400 cm³ of this solution. [3 marks]
Answer: 10 g
Worked example: Higher Concentration Calculation
Calculate the mass of sodium chloride in 250 cm³ of a solution with concentration 80 g/dm³. [3 marks]
Answer: 20 g
Concentration questions are mark-heavy in GCSE exams. Get the method right, and you'll pick up most marks even if your final answer has a small error.
The biggest trap is unit confusion. Examiners deliberately mix g/dm³ with cm³ volumes to catch students who don't convert. Always pause and check: do my units match?
Master this formula and you'll never lose marks on concentration questions again. The key is methodical working and careful attention to units - exactly what examiners reward.
Exam precision note: In Calculating Mass of Solute in Solutions - Concentration of solutions - Use of amount of substance in relation to masses of pure substances, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
This GCSE topic uses mass concentration, usually written in g/dm3. That is different from molar concentration, which is written in mol/dm3 and belongs to later chemistry work. Keeping that distinction clear helps students focus on the quantity they are actually calculating here: the mass of solute in a known volume of solution. It also explains why unit conversion is so important, because the volume unit must match the concentration unit before multiplying.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The concentration formula is concentration = mass of solute ÷ volume of solution, measured in g/dm³. It can be rearranged to mass = concentration × volume, so knowing the concentration and volume gives the mass of solute.
The concentration of a solution is measured as mass per unit volume, in g/dm³ or g/cm³. At GCSE it is usually written in g/dm³, which is a mass concentration.
Mass of solute = concentration × volume, with the volume in dm³ when the concentration is in g/dm³. For 400 cm³ of a 25 g/dm³ solution, the volume is 400 ÷ 1000 = 0.4 dm³, so the mass = 25 × 0.4 = 10 g.
Mass concentration is measured in g/dm³ and gives the mass of solute in a volume of solution, while molar concentration is measured in mol/dm³ and belongs to later chemistry work.
Units must match in concentration calculations because concentration can be given in g/dm³ or g/cm³ and volume in dm³ or cm³; if they do not match, the answer will be wrong by a factor of 1000. Convert the volume first, for example 250 cm³ = 0.25 dm³.
The mass of sodium chloride in a solution is found by multiplying its concentration by the volume in dm³. In 250 cm³ of an 80 g/dm³ solution, 250 cm³ = 0.25 dm³, so the mass = 80 × 0.25 = 20 g.
There are 10 g of solute in 400 cm³ of a 25 g/dm³ solution. The volume is converted first, 400 ÷ 1000 = 0.4 dm³, then mass = concentration × volume = 25 g/dm³ × 0.4 dm³ = 10 g.
A solution is more concentrated when more solute is dissolved in the same volume of solution. Like stronger coffee, with more coffee grounds in the same amount of water, a higher concentration means more grams of solute in each dm³.