You need to design an experiment to determine the percentage, by mass, of water in copper(II) sulfate crystals. Your plan should: • describe, or sketch, the apparatus that can be used to remove the water, • state all the weighings that ought to be taken, • explain how these can be used to calculate the percentage, by mass, of water.
The formula for copper(II) sulfate crystals is $\text{CuSO}_4\cdot y\text{H}_2\text{O}$, where $y$ represents the number of moles of water of crystallisation in 1 mole of crystals. A student carries out an experiment and finds $y = 4$. The correct value of $y$ for her sample is $5$. Suggest an error in her experiment that would produce this difference. Explain how this error would cause the lower value of $y$ and suggest how the experiment could be improved so that the correct value of $y$ is obtained.