When solutions are mixed together, precipitates sometimes form.
Lead(II) hydroxide is an insoluble compound. It is formed as a precipitate when solutions of the soluble compounds lead(II) nitrate and sodium hydroxide are mixed.
When solutions of the soluble compounds potassium chloride and sodium sulfate are mixed, no precipitate is formed.
Complete the table to show the results of mixing solutions of some compounds.
| sodium hydroxide solution | sodium sulfate solution | |
|---|---|---|
| lead(II) nitrate solution | precipitate of lead(II) hydroxide | ............................................................ |
| potassium chloride solution | ............................................................ | no precipitate |
| copper(II) sulfate solution | precipitate of copper(II) hydroxide | ............................................................ |
When solutions of barium chloride and sodium sulfate are mixed, a precipitate of barium sulfate and a solution of sodium chloride are produced.
The equation for the reaction is:
BaCl2(..........)+Na2SO4(..........)→BaSO4(..........)+2NaCl(..........) \text{BaCl}_2(\text{..........}) + \text{Na}_2\text{SO}_4(\text{..........}) \rightarrow \text{BaSO}_4(\text{..........}) + 2\text{NaCl}(\text{..........}) BaCl2(..........)+Na2SO4(..........)→BaSO4(..........)+2NaCl(..........)Complete the equation by inserting the state symbols.
In order to prepare a pure, dry sample of barium sulfate, a student took the mixture produced in part (b). He then:
Why did the student filter the mixture?
Why did the student wash the solid residue?
Why is it better to use distilled water rather than tap water to wash the solid residue?
Why did the student leave the solid in a warm place?
23 exam-style questions on Edexcel IGCSE Chemistry Acids, bases and salt preparations. Each one has a worked solution and a mark scheme showing where the marks go.