A laboratory tests a sample of compound H before and after a purification step.
The accepted melting point of compound H is 63 ∘C63\ ^\circ\text{C}63 ∘C and its accepted boiling point is 181 ∘C181\ ^\circ\text{C}181 ∘C.
The table shows the temperatures at which each sample melted and boiled.
| Sample | Melting temperature | Boiling temperature |
|---|---|---|
| Before purification | 57 ∘C57\ ^\circ\text{C}57 ∘C | 173 ∘C173\ ^\circ\text{C}173 ∘C |
| After purification | 63 ∘C63\ ^\circ\text{C}63 ∘C | 181 ∘C181\ ^\circ\text{C}181 ∘C |
What do these results show?
The sample was purer before purification because lower measured temperatures show greater chemical purity.
The purification step formed a different compound because both measured temperatures changed during the process.
The sample was already pure before purification because its temperatures were close to the accepted values.
The purification step was successful because both temperatures after purification match the accepted values.
113 exam-style questions on AQA GCSE Chemistry 8.1 Purity, formulations and chromatography, covering 8.1.1 Pure substances, 8.1.2 Formulations, and 8.1.3 Chromatography. Each one has a worked solution and a mark scheme showing where the marks go.