Concentration of Solutions
Concentration tells us how much of a substance (solute) is dissolved in a certain volume of a solvent. It is usually measured in grams per decimetre cubed (g/dm³) or moles per decimetre cubed (mol/dm³). A concentrated solution has a large amount of solute in a small amount of solvent.
Full topic guide: the detailed syllabus page with worked examples and common mistakes lives at studyvector.co.uk/gcse/chemistry/quantitative-chemistry/concentration-of-solutions.
Topic preview: Concentration of Solutions
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Topic explanation
Concentration tells us how much of a substance (solute) is dissolved in a certain volume of a solvent. It is usually measured in grams per decimetre cubed (g/dm³) or moles per decimetre cubed (mol/dm³). A concentrated solution has a large amount of solute in a small amount of solvent.
Concentration of Solutions is easiest to revise when it is treated as a precise exam behaviour, not a loose note-taking category. In GCSE Chemistry, the goal is to recognise how the topic appears in a question, identify the command word, and decide what evidence, method, or vocabulary earns marks. StudyVector keeps this page tied to AQA · Edexcel · OCR language where coverage is available, then routes practice towards the same topic so revision moves from explanation into retrieval.
A strong revision session starts with a short recall check. Write down the rule, definition, process, or method linked to Concentration of Solutions before looking at any notes. Then answer one exam-style prompt and compare your answer with the mark-scheme logic: did you make a clear point, support it with the right step, and avoid drifting into a nearby topic? This matters because many lost marks come from almost-correct answers that do not match the expected structure.
Use this guide as the first layer: understand the topic, look at the worked examples, complete the mini quiz, then move into full practice. The full StudyVector practice loop is designed to capture whether mistakes are caused by knowledge, method, language, or timing. That distinction is important. If the error is factual, you need reteaching. If the error is method-based, you need a worked retry. If the error is wording, you need command-word calibration. That is how Concentration of Solutions becomes a controlled revision target rather than another page in a folder.
Lost marks → repair task
Why marks are usually lost here
These are the error patterns StudyVector looks for after an attempt. The goal is not a generic explanation; it is one repair move and one follow-up question.
Unit, formula, or method slip
Examiner move: Select the correct method and keep units, substitutions, signs, and rounding visible.
Repair drill: Redo the calculation or method line slowly, naming the formula before substituting values.
Missing chain of reasoning
Examiner move: Show the link between point, method, evidence, and conclusion instead of jumping to the final line.
Repair drill: Write the missing because/therefore step, then retry one isomorphic question.
Command-word miss
Examiner move: Answer the action in the command word before adding extra detail.
Repair drill: 60-second rewrite: start the answer with explain, compare, evaluate, state, or calculate in mind.
Mini quiz
Use these checks before full practice. They test topic recognition, exam technique, and whether you can connect the explanation to a marked response.
1. What should you check first when a Concentration of Solutions question appears in GCSE Chemistry?
- A.The command word and the exact topic focus
- B.The longest paragraph in your notes
- C.A memorised answer from a different topic
2. Which revision action gives the strongest evidence that Concentration of Solutions is improving?
- A.Rereading the explanation twice
- B.Answering a timed exam-style question and reviewing lost marks
- C.Highlighting every key phrase in the topic notes
Sample questions
Topic-specific public question previews are still being reviewed. We keep them off public pages until the topic match is safe.
Exam tips
- Read the command word carefully — "explain" needs reasons; "state" expects a short fact.
- For Concentration of Solutions, show structured working even when you are practising multiple choice — it builds accuracy under time pressure.
- Mark yourself against the mark scheme style: one clear point per mark, in logical order.
- Come back to this topic after a day or two; short spaced reviews beat one long cram.
Worked examples
Example 1
Modelled exam response
To find the concentration in mol/dm³ of a solution made by dissolving 4g of NaOH (Mr = 40) in 250 cm³ of water: 1. Moles of NaOH = 4g / 40 = 0.1 mol. 2. Volume in dm³ = 250 cm³ / 1000 = 0.25 dm³. 3. Concentration = 0.1 mol / 0.25 dm³ = 0.4 mol/dm³.
Example 2
Identify the task before answering
Question type: a Concentration of Solutions prompt asks for a clear response in GCSE Chemistry. Step 1: underline the command word. Step 2: name the exact part of Concentration of Solutions being tested. Step 3: decide whether the mark scheme wants a definition, method, explanation, comparison, or calculation. Why it works: most weak answers fail before the content starts because they answer the topic generally rather than the exact exam task.
Example 3
Turn feedback into a repair task
Suppose your answer shows partial understanding but loses marks for precision. First, rewrite the missing mark as a short target: "I need to state the mechanism, unit, reason, or evidence explicitly." Then answer one similar question without notes. Finally, compare the second attempt with the first and check whether the same mark was recovered. Why it works: Concentration of Solutions improves faster when feedback creates a specific retry, not another passive reading session.
Next revision routes from this subject
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Common mistakes
- Forgetting to convert volumes from cm³ to dm³. Remember that 1 dm³ = 1000 cm³, so you must divide cm³ by 1000.
- Confusing the terms solute, solvent, and solution. The solute is what dissolves, the solvent does the dissolving, and the solution is the final mixture.
- Using the wrong formula. For concentration in g/dm³, use Mass / Volume. For mol/dm³, use Moles / Volume.
Exam board notes
Concentration calculations are a higher-tier topic for all exam boards. You must be comfortable with both g/dm³ and mol/dm³ and be able to convert between them. Titration calculations also rely heavily on this knowledge.
FAQs
What is a saturated solution?
A saturated solution is one in which the maximum amount of solute has been dissolved in a solvent at a given temperature. No more solute can be dissolved.
How does temperature affect concentration?
For most solid solutes, increasing the temperature of the solvent increases the amount of solute that can dissolve, allowing for a more concentrated solution to be made.
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