Grade 10 · CAPS

Grade 10 Quantitative Aspects of Chemical Change

Physical Sciences practice questions and a worked example

Grade 10 quantitative aspects of chemical change covers the mole and calculations from equations. The questions here ask you to calculate molar mass and numbers of moles, use molar volume and concentration, find empirical and molecular formulae and water of crystallisation, and calculate masses, percentage composition and percentage yield from balanced equations. They come from the DBE Grade 10 common Paper 2 for November 2016, 2017 and 2018, each with the answer from the marking guideline.

Worked example

The unbalanced chemical equation (i) and the word equation (ii) for two chemical reactions are shown below. (i) Cℓ₂(g) + H₂(g)→ HCℓ(g) (ii) aluminium carbonate → aluminium oxide + carbon dioxide 6.6 Calculate the percentage composition of hydrogen chloride.

Answer & explanation

M(HCl) = 1 + 35,5 = 36,5 g·mol⁻¹ %H = (1/36,5) × 100 = 2,74 % %Cl = (35,5/36,5) × 100 = 97,26 %
To find the percentage composition of hydrogen chloride (HCl), we first calculate its molar mass. The molar mass of hydrogen (H) is 1 g/mol, and the molar mass of chlorine (Cl) is 35.5 g/mol. Therefore, the molar mass of HCl is calculated as follows: 1. Calculate the molar mass of HCl: g/mol. 2. Calculate the percentage of hydrogen in HCl: . 3. Calculate the percentage of chlorine in HCl: . Thus, the percentage composition of hydrogen chloride is 2.74% hydrogen and 97.26% chlorine.

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Quantitative Aspects of Chemical Change

Question 1 of 2

1.7 In a 20 g sample of molecules, which sample below has the greatest number of moles?
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More practice questions

Explore additional Grade 10 Quantitative Aspects of Chemical Change questions.

  • 2
    Potassium chloride dissociates in water to form an electrolyte. 7.4 Calculate the percentage potassium in potassium chloride.
  • 3
    8.1.1 Define the term empirical formula.
  • 4
    8.1 The empirical formula of a certain compound is to be determined. On analysis of a sample of the compound it was found to contain 40% C, 6,6% H and 53,3% O. 8.1.2 Determine the empirical formula of the compound. Show ALL calculations.
  • 5
    8.1 The empirical formula of a certain compound is to be determined. On analysis of a sample of the compound it was found to contain 40% C, 6,6% H and 53,3% O. 8.1.3 If the molecular mass of the compound is 60 g·mol⁻¹, calculate the molecular formula of the compound.

Common mistakes

  • Skipping the mole ratio. Use the coefficients in the balanced equation to go from the moles of one substance to another.
  • Using cm³ in c = n/V. Change the volume to dm³ first (divide by 1 000).
  • Rounding too early. Keep at least two decimal places until the final answer.

More Grade 10 Physical Sciences topics

Aligned to CAPS Grade 10 Physical Sciences — Quantitative Aspects of Chemical Change. Curriculum source: CAPS for the FET Phase, Department of Basic Education.

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