A student has a white solid, S. It melts sharply at 133 ∘C133\,^\circ\mathrm{C}133∘C.
Two pure substances, P and Q, both melt at 133 ∘C133\,^\circ\mathrm{C}133∘C.
The student mixes some of S with pure P, and some of S with pure Q. The student then measures the melting temperature of each mixture.
| Mixture | Melting temperature (∘C^\circ\mathrm{C}∘C) |
|---|---|
| S mixed with P | 124 to 129 |
| S mixed with Q | 133 |
Which conclusion is correct?
S is P, because S and P have the same melting point.
S is Q, because adding Q to S does not lower the melting point or make it melt over a range.
S is a mixture of P and Q, because both mixtures melt close to 133 ∘C133\,^\circ\mathrm{C}133∘C.
S is impure, because one of the mixtures melts over a range of temperatures.
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.