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 

ORIGINAL mole Q

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 (9–1) chemistry science courses.

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

(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

(1) V_CO2 = mol Na₂CO₃ x 24000 = 0.76 ÷ 106 x 24000 = 172cm³

(2) V_CO2 = 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, V_H2 = 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

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OTHER CALCULATION PAGES

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

   • Reacting masses, concentration of solution and volumetric titration calculations (NOT using moles)

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

    • 14.1 % purity of a product 14.2a % reaction yield 14.2b atom economy 14.3 dilution of solutions

    • 14.4 water of crystallisation calculation  14.5 how much of a reactant is needed?

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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