A student is given two samples of a white solid, each sold as lauric acid. The student melts each sample and then records its temperature every minute as it cools.
| Time / min | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Temperature of sample 1 / °C | 60 | 52 | 44 | 44 | 44 | 44 | 38 |
| Temperature of sample 2 / °C | 60 | 51 | 43 | 40 | 38 | 36 | 33 |
Deduce which sample is pure lauric acid. Justify your answer using the data for both samples.
State the melting point of pure lauric acid.
A bottle of spring water has the label "pure spring water". The label also gives the dissolved substances in the water.
| Dissolved substance | Mass in 1.0 dm3\mathrm{dm^{3}}dm3 / mg |
|---|---|
| calcium ions | 55 |
| magnesium ions | 19 |
| sodium ions | 24 |
| chloride ions | 42 |
| sulfate ions | 210 |
Explain why the spring water is not pure in the chemical sense but is still suitable for drinking.
The student evaporates 250 cm3\mathrm{cm^{3}}cm3 of the spring water to dryness. Calculate the mass, in grams, of solid the student should obtain according to the label.
The student actually obtains 0.12 g of solid. Suggest two reasons why this is more than the mass calculated in (c)(ii).
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.