The table shows information about the effect of adding sodium hydroxide solution to solutions containing magnesium ions, calcium ions or aluminium ions.
| Ion in solution | Effect of adding a few drops of sodium hydroxide solution | Effect of adding excess sodium hydroxide solution |
|---|---|---|
| magnesium, Mg2+\text{Mg}^{2+}Mg2+ | white precipitate forms | white precipitate remains |
| calcium, Ca2+\text{Ca}^{2+}Ca2+ | white precipitate forms | white precipitate remains |
| aluminium, Al3+\text{Al}^{3+}Al3+ | white precipitate forms | white precipitate disappears |
A student is provided with a sample of a white solid. The student dissolves some of the white solid in water and then adds a few drops of sodium hydroxide solution. A white precipitate forms. She concludes that the sample contains calcium ions. Explain whether the student’s conclusion is valid.
Give a different test to show that the white solid contains calcium ions. Identify the test and the expected result.
A hydrated salt has the formula AB2⋅xH2O\text{AB}_2 \cdot x\text{H}_2\text{O}AB2⋅xH2O where A\text{A}A is a positive metal ion and B\text{B}B is a negative ion. When the hydrated salt is heated, this reaction occurs:
AB2⋅xH2O→AB2+xH2O \text{AB}_2 \cdot x\text{H}_2\text{O} \rightarrow \text{AB}_2 + x\text{H}_2\text{O} AB2⋅xH2O→AB2+xH2OA scientist heats a sample of the hydrated salt until all the water has been lost. She records the mass of the salt before and after heating. The table shows her results.
| Mass of hydrated salt | Mass of salt after heating |
|---|---|
| 2.94 g | 2.22 g |
Describe how the scientist could make sure that all the water has been lost.
Use the scientist’s results to find the value of x x\,x in AB2⋅xH2O\text{AB}_2 \cdot x\text{H}_2\text{O}AB2⋅xH2O. [Mr of AB2=111,Mr of H2O=18][M_{\text{r}} \text{ of } \text{AB}_2 = 111, \quad M_{\text{r}} \text{ of } \text{H}_2\text{O} = 18][Mr of AB2=111,Mr of H2O=18]
Describe how the scientist could use a solution of the salt to find out if the negative ions are chloride ions.
The test shows that the negative ions are chloride ions. Calculate the relative atomic mass of metal A\text{A}A using the formula and MrM_{\text{r}}Mr value of the anhydrous salt, AB2\text{AB}_2AB2.
Identify metal A\text{A}A.
35 exam-style questions on Edexcel IGCSE Chemistry Chemical tests. Each one has a worked solution and a mark scheme showing where the marks go.