Edexcel IGCSE Chemistry Practical Contexts

Practise Edexcel IGCSE Chemistry practical contexts by applying chemical ideas to excess reagents, gas expansion and measurement precision.

Exam points

Explain bubbles at the start of heating as air or gas expanding in the apparatus.
Justify why exact mass or volume measurement is unnecessary when a reagent is in excess.

[Maximum number: 1]

A student uses this apparatus to investigate the rate of reaction between dilute sulfuric acid and an excess of small pieces of zinc.

Figure for Question Apply chemistry in practical contexts question 1 — Edexcel IGCSE Chemistry

This is the student's method.
Step 1 use $50 \mathrm{~cm}^{3}$ of dilute sulfuric acid
Step 2 add approximately 5 g of small zinc pieces to the sulfuric acid
Step 3 quickly connect the gas syringe
Step 4 record the reading on the gas syringe every 30 seconds until the reaction stops

Give a reason why the mass of zinc pieces does not need to be measured accurately.

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Apply chemistry in practical contexts question 1