Edexcel IGCSE Chemistry 2.39 Preparing Soluble Salts From Insoluble Reactants Questions

Practise soluble-salt questions by adding excess solid, filtering unreacted material and crystallising pure hydrated salts.

Exam points

Explain why excess metal or insoluble reactant ensures all the acid has reacted.
Sequence filtration, heating, cooling and drying to obtain pure hydrated salt crystals.
Link filtering to removing excess zinc, magnesium or other unreacted insoluble solid.

[Maximum number: 1]

This question is about magnesium metal and its compounds.

A student uses this method to make a solution of magnesium chloride.

Step 1. measure $25 \mathrm{~cm}^{3}$ of dilute hydrochloric acid into a beaker
Step 2 add magnesium powder a little at a time
Step 3 keep adding magnesium powder until it is in excess
Step 4 remove the excess magnesium powder by filtration

This is the equation for the reaction.

Figure for Question Edexcel IGCSE Chemistry 2.39 Preparing Soluble Salts From Insoluble Reactants Questions question 1 — Edexcel IGCSE Chemistry

Give a reason why the student adds an excess of magnesium in step 3.

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Edexcel IGCSE Chemistry 2.39 Preparing Soluble Salts From Insoluble Reactants Questions question 1