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

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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(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

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