A company makes paracetamol for tablets. Pure paracetamol melts at 169 °C. A quality-control scientist measures the melting point of four batches.
| Batch | Melting point |
|---|---|
| 1 | 169 °C |
| 2 | melts between 162 °C and 166 °C |
| 3 | 169 °C |
| 4 | melts between 158 °C and 165 °C |
Give the numbers of the two batches that are pure.
Describe two ways in which the melting point of an impure sample is different from the melting point of a pure sample.
Deduce which batch contains the most impurity. Justify your answer.
A worker says batch 1 must be pure because it is a white crystalline solid. Explain why this is not good evidence that batch 1 is pure.
Suggest why it is important that the paracetamol used in tablets is pure.
48 exam-style questions on Edexcel GCSE Chemistry 3.2 Methods of separating and purifying substances, covering 3.2.1 Pure substances and mixtures, 3.2.2 Techniques for separating mixtures, 3.2.3 Paper chromatography and Rf values, and 3.2.4 Making water potable. Each one has a worked solution and a mark scheme showing where the marks go.