CCEA GCSE Chemistry
CCEA GCSE Chemistry 2.6 Quantitative Chemistry Exam Questions
Free CCEA GCSE Chemistry revision for 2.6 Quantitative Chemistry: what you need to know, common mistakes and exam-style questions with answers. Covers solution concentration in mol per dm3 and g per dm3, acid-alkali titrations, molar gas volume, Avogadro's Law and atom economy.
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About CCEA GCSE Chemistry 2.6 Quantitative Chemistry
Quantitative Chemistry in Unit 2 of CCEA GCSE Chemistry extends the mole calculations from Unit 1 to solutions and gases. You need to calculate concentration in mol per dm3 and g per dm3, carry out titrations accurately in the prescribed practical, and use titration results to find an unknown concentration. The topic also covers the molar gas volume, Avogadro's Law for reacting gas volumes and atom economy as a measure of how efficient a process is. It builds directly on 1.7 and links to acids and salts. Examiners regularly set multi-step titration calculations and expect correct unit conversions from cm3 to dm3.
What you need to know
- Concentration Concentration (mol per dm3) = moles / volume (dm3). Convert cm3 to dm3 by dividing by 1000. Concentration in g per dm3 = concentration in mol per dm3 x Mr.
- Prescribed practical: titration Use a pipette to measure 25.0 cm3 of alkali into a conical flask, add a few drops of indicator and add acid from a burette, swirling, until the indicator just changes colour. Record burette readings to 0.05 cm3 and repeat until you have concordant titres (within 0.10 cm3), then average them.
- Titration calculations Find moles of the substance with known concentration and volume, use the mole ratio from the balanced equation, then divide by the volume of the other solution in dm3 to find its concentration.
- Molar gas volume One mole of any gas occupies 24 dm3 (24 000 cm3) at room temperature and pressure. Volume (dm3) = moles x 24.
- Avogadro's Law Equal volumes of all gases at the same temperature and pressure contain the same number of molecules. So the ratio of gas volumes in a reaction equals the mole ratio in the equation, for example 2H2 + O2 → 2H2O means 2 volumes of hydrogen react with 1 of oxygen.
- Atom economy Atom economy = Mr of desired product / sum of Mr of all reactants x 100. A high atom economy means less waste and is better for sustainability.
Common mistakes in 2.6 Quantitative Chemistry
- Forgetting to convert cm3 to dm3 before using concentration = moles / volume.
- Including rough titres in the average. Use only concordant results.
- Ignoring the mole ratio in titrations such as sulfuric acid with sodium hydroxide, where the ratio is 1 : 2.
- Using 24 dm3 for liquids or solids. The molar volume applies only to gases.
- Confusing atom economy with percentage yield. Atom economy is calculated from the equation, not from experimental masses.
Try three 2.6 Quantitative Chemistry exam-style questions
1. 25.0 cm3 of sodium hydroxide solution was neutralised by 20.0 cm3 of 0.100 mol per dm3 hydrochloric acid. Calculate the concentration of the sodium hydroxide. (3 marks)
Show the mark scheme answer
Moles HCl = 0.100 x 20.0 / 1000 = 0.00200; moles NaOH = 0.00200 (1 : 1 ratio); concentration = 0.00200 / 0.0250 = 0.0800 mol per dm3.
2. Calculate the volume of carbon dioxide at room temperature and pressure produced from 0.25 mol of calcium carbonate reacting with excess acid. (2 marks)
Show the mark scheme answer
Moles CO2 = 0.25; volume = 0.25 x 24 = 6.0 dm3.
3. Calculate the atom economy for making calcium oxide by CaCO3 → CaO + CO2. (Mr CaCO3 = 100, CaO = 56) (2 marks)
Show the mark scheme answer
56 / 100 x 100; = 56%.
2.6 Quantitative Chemistry FAQs
What does CCEA GCSE Chemistry 2.6 Quantitative Chemistry cover?
It covers concentration in mol per dm3 and g per dm3, titrations and titration calculations, molar gas volume, Avogadro's Law and atom economy.
Which unit is 2.6 Quantitative Chemistry examined in?
It is examined in the Unit 2 written paper, and the titration practical can also be assessed in Unit 3 Practical Skills.
What should I remember for titration practical questions?
Know the apparatus (pipette, burette, conical flask, white tile), why you swirl and add dropwise near the end point, how to read the bottom of the meniscus and what concordant results are.
