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Edexcel IGCSE Chemistry 2.39 soluble salt preparation

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

Syllabus
First assessment 2019
Course
Chemistry 4CH1

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.

2.39 Preparing soluble salts from insoluble reactants question 1

[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 cm325 \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 2.39 Preparing soluble salts from insoluble reactants question 1 — Edexcel IGCSE Chemistry

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

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