Edexcel IGCSEChemistryGeneral Applications7 Marks

The relative atomic masses of elements are given in the Periodic Table.

(a)Calculate the number of moles in 4.9 g of sulfuric acid (H₂SO₄). (Relative atomic masses: H = 1, O = 16, S = 32)[2]
(b)A compound contains 2.4 g of carbon, 0.4 g of hydrogen and 3.2 g of oxygen.[5]
(b)(i)Calculate the empirical formula of the compound.[3]
(b)(ii)If the relative molecular mass of the compound is 60, what is its molecular formula?[2]

Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

5(a)
M1 for Mr of H₂SO₄ = (2 × 1 + 32 + 4 × 16) = 98 (1)
A1 for moles = 4.9 / 98 = 0.05 mol (1)
5(b)(i)
M1 for calculating moles of each element: C: 2.4/12 = 0.2 mol H: 0.4/1 = 0.4 mol O: 3.2/16 = 0.2 mol (1)
M1 for dividing by smallest number of moles (0.2): C: 0.2/0.2 = 1 H: 0.4/0.2 = 2 O: 0.2/0.2 = 1 (1)
A1 for empirical formula CH₂O (1)
5(b)(ii)
M1 for Mr of empirical formula (CH₂O) = 12 + (2 × 1) + 16 = 30 (1)
A1 for molecular formula = (60 / 30) × CH₂O = C₂H₄O₂ (1)

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