A student tries to make a pure, dry sample of hydrated nickel(II) sulfate crystals. She uses dilute sulfuric acid and solid nickel(II) carbonate. This is the student's method:
Her sample of nickel(II) carbonate contains a small amount of solid impurity that dissolves in water, but does not react with the acid.
State why it is not necessary to have a precise measurement of the volume of sulfuric acid in step 1.
State why the acid is warmed in step 2.
Suggest why a glass rod, rather than a metal spatula, is used to stir the mixture in step 3.
State how the student will know when the nickel(II) carbonate stops reacting in step 4.
State why the method used in step 6 will not produce a pure sample of hydrated nickel(II) sulfate crystals.
Describe how the student could produce a pure, dry sample of crystals from the filtrate in step 5.
The table below shows the formula and colour of three different types of nickel(II) sulfate.
| Formula | Colour |
|---|---|
| NiSO4\text{NiSO}_4NiSO4 | yellow |
| NiSO4⋅H2O\text{NiSO}_4\cdot\text{H}_2\text{O}NiSO4⋅H2O | pale green |
| NiSO4⋅6H2O\text{NiSO}_4\cdot6\text{H}_2\text{O}NiSO4⋅6H2O | green |
When water is added very slowly to solid NiSO4\text{NiSO}_4NiSO4, the colour changes from yellow to pale green and then to green.
Write a chemical equation for the change from the pale green solid to the green solid.
Which of these words describes the change taking place when the green solid is heated to form the yellow solid?
