GCSE-A level Chemistry Calculations: Answers to advanced Q's using the mole concept

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Answers to the more advanced level mole concept calculations

Doc Brown's Chemistry - GCSE/IGCSE/GCE (basic A level) Online Chemical Calculations

ANSWERS to Part 7 - the more advanced mole Q's 

The ORIGINAL mole Questions

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Quantitative chemistry calculations This page has the answers to the more advanced mole based questions from calculations section 7. for more advanced chemistry students. Online practice exam chemistry CALCULATIONS and solved problems for KS4 Science GCSE/IGCSE CHEMISTRY and basic starter chemical calculations for A level AS/A2/IB. These revision notes and practice questions on how to do chemical calculations and worked examples should prove useful for the new AQA, Edexcel and OCR GCSE (91) chemistry science courses.

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Mole calculations introduction * Molar gas volume * Advanced Redox titration Q's * Non-redox titration Q's

Qa7.1 (a) f. mass Al2O3 = 102, 2 102 x 3 x 6.02 x 1023 = 3.54 x 1022 oxide ions

(b) f. mass H2 = 2, 3 2 x 6.02 x 1023 = 9.03 x 1023 molecules

(c) 1.2 24000 x 6.02 x 1023 = 3.01 x 1019 molecules

(d) f. mass Cl2 = 71, 3 71 x 6.02 x 1023 = 2.54 x 1022 molecules

(e) Neon exists as single atoms (Ar = 20), 10 20 x 6.02 x 1023 = 3.01 x 1023 atoms

(f) 2Na + 2H2O ==> 2NaOH + H2,

1 mole sodium gives 0.5 moles hydrogen,

mole Na = 0.2 23 = 0.008696, so mole H2 = 0.008696 2 = 0.004348

so volume H2 = 0.004348 x 24000 = 104.3 cm3 or 0.104 dm3

(g) e.g. Mg + 2HCl ==> MgCl2 + H2

1 mole magnesium gives 1 mole hydrogen, mole Mg = 2 24.3 = 0.0823

so mole H2 = 0.0823, so volume H2 = 0.0823 x 24 = 1.975 dm3

(h) both 1 mole of Na2CO3 or NaHCO3 will give 1 mole of CO2

(1) VCO2 = mol Na2CO3 x 24000 = 0.76 106 x 24000 = 172cm3

(2) VCO2 = mol NaHCO3 x 24000 = 0.76 84 x 24000 = 217cm3

(i) Zn + 2HCl ==> ZnCl2 + H2 , mole H2 = mole HCl 2

mol HCl = 50 1000 x 0.2 = 0.01 mol

so mole H2 = 0.005, VH2 = 0.005 x 24000 = 120cm3

(j) CaCO3 + 2HCl ==> CaCl2 + H2O + CO2

mole CO2 = mole HCl 2, mol HCl = 75 1000 x 0.05 = 0.00375 mol

so mole CO2 = 0.001875, VCO2 = 0.001875 x 24000 = 45cm3

Above is typical periodic table used in GCSE science-chemistry specifications in doing chemical calculations, and I've 'usually' used these values in my exemplar calculations to cover most syllabuses


  1. What is relative atomic mass?, relative isotopic mass and calculating relative atomic mass

  2. Calculating relative formula/molecular mass of a compound or element molecule

  3. Law of Conservation of Mass and simple reacting mass calculations

  4. Composition by percentage mass of elements in a compound

  5. Empirical formula and formula mass of a compound from reacting masses (easy start, not using moles)

  6. Reacting mass ratio calculations of reactants and products from equations (NOT using moles) and brief mention of actual percent % yield and theoretical yield, atom economy and formula mass determination

  7. Introducing moles: The connection between moles, mass and formula mass - the basis of reacting mole ratio calculations (relating reacting masses and formula mass)

  8. Using moles to calculate empirical formula and deduce molecular formula of a compound/molecule (starting with reacting masses or % composition)

  9. Moles and the molar volume of a gas, Avogadro's Law

  10. Reacting gas volume ratios, Avogadro's Law and Gay-Lussac's Law (ratio of gaseous reactants-products)

  11. Molarity, volumes and solution concentrations (and diagrams of apparatus)

  12. How to do acid-alkali titration calculations, diagrams of apparatus, details of procedures

  13. Electrolysis products calculations (negative cathode and positive anode products)

  14. Other calculations e.g. % purity, % percentage & theoretical yield, dilution of solutions (and diagrams of apparatus), water of crystallisation, quantity of reactants required, atom economy

  15. Energy transfers in physical/chemical changes, exothermic/endothermic reactions

  16. Gas calculations involving PVT relationships, Boyle's and Charles Laws

  17. Radioactivity & half-life calculations including dating materials


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