IB Chemistry HL S1.4 Counting particles by mass: the mole questions

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Question 1

Paper 2Medium8 marks

A quality-control test estimates the hydrogen peroxide concentration in a solution labelled 10.0 g dm⁻³. A 10.00 cm³ sample is completely decomposed according to the equation:

2 H₂O₂(aq) → 2 H₂O(l) + O₂(g)

The oxygen produced has a volume of 36.0 cm³. A 25.0 cm³ sample of nitrogen at the same temperature and pressure contains 1.00 × 10⁻³ mol of nitrogen. Assume both gases behave ideally and that no oxygen is lost. Use M(H₂O₂) = 34.0 g mol⁻¹.

(a)

Determine the amount, in mol, of oxygen produced.

[2]
(b)

Calculate the molar concentration, [H₂O₂], in the original solution, in mol dm⁻³.

[3]
(c)

Calculate the mass concentration of hydrogen peroxide in the original solution, in g dm⁻³.

[1]
(d)

Using the labelled concentration as the reference, calculate the percentage by which your result in (c) differs from the label, and state whether the measured value is higher or lower.

[2]

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