# Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas. The equation for this reaction is: Zn + 2HCl → ZnCl₂ + H₂. The relative atomic mass of zinc is 65. The relative atomic mass of chlorine is 35.5. The relative atomic mass of hydrogen is 1. A student reacts a sample of zinc with excess hydrochloric acid in an open container and measures the mass of the container throughout the reaction. The student notices the total mass of the container decreases during the reaction. Explain why the mass decreases, and explain why the total mass of zinc chloride produced is greater than the mass of zinc used.

> AQA GCSE Chemistry (8462) — 4.3.2 Use of amount of substance in relation to masses of pure substances · Explain · 4 marks

## Mark scheme (4 marks)

1. Hydrogen gas is released/escapes into the atmosphere/surroundings
2. The mass of the hydrogen gas is not accounted for / is lost from the system
3. Zinc chloride contains chlorine atoms (from the hydrochloric acid) as well as zinc atoms
4. No atoms are lost or made during the reaction (conservation of mass), so the mass of chlorine added to the zinc increases the mass of the product

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