Some solder is an alloy of tin and lead. It is made to a fixed recipe and melts between 183 ∘C183\,^\circ\mathrm{C}183∘C and 190 ∘C190\,^\circ\mathrm{C}190∘C.
A student says:
"Solder melts over a range of temperatures, so it is impure and must be a poor-quality product."
Which response to the student is correct?
The student is correct, because a good-quality product must be a pure substance.
The student is wrong, because alloys are compounds, so solder must melt at a sharp temperature.
The student is partly correct. Solder is a mixture, but it is a formulation made in measured amounts so that it has useful properties.
The student is wrong, because nothing harmful has been added to the solder, so it is pure.
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.