A carton of orange juice has the label "100% pure orange juice".
What is meant by a pure substance in chemistry?
A chemist says the orange juice is not pure.
Explain why the chemist says this, and what the label means by "pure".
A student tests three samples of benzoic acid, P, Q and R. Pure benzoic acid melts at 122 °C.
The table shows the results.
| Sample | Melting point (°C) |
|---|---|
| P | 122 |
| Q | 115 to 119 |
| R | 108 to 117 |
Which sample is pure? Give a reason for your answer.
Which sample is the least pure? Give a reason for your answer.
51 exam-style questions on OCR GCSE Chemistry 2.1 Purity and separating mixtures, covering 2.1.1 Pure substances and melting point data, 2.1.2 Relative formula mass and empirical formula, 2.1.3 Formulations as useful mixtures, 2.1.4 Techniques for separating mixtures, and 2.1.5 Chromatography and Rf values. Each one has a worked solution and a mark scheme showing where the marks go.