A research chemist is working with a mixture of three substances: quartz powder, cobalt(II) chloride, and water.
The table below shows some physical properties of these three substances:
| Substance | Melting point (∘C^\circ \text{C}∘C) | Boiling point (∘C^\circ \text{C}∘C) | Solubility in water |
|---|---|---|---|
| Quartz powder | 1713 | 2950 | Insoluble |
| Cobalt(II) chloride | 735 | 1049 | Soluble |
| Water | 0 | 100 | - |
Describe how the chemist can separate this mixture to obtain pure, dry samples of all three individual substances. Explain the physical principles behind why each separation method works.
The chemist then separates two solid compounds, A and B. She wants to verify whether her samples of solid A are pure. She measures the melting point characteristics of four different samples of solid A. The results of her measurements are shown below:
| Sample | Melting point (∘C^\circ \text{C}∘C) |
|---|---|
| 1 | 157 |
| 2 | 148 |
| 3 | 146–151 |
| 4 | 158–162 |
The chemist knows from a reference database that a completely pure sample of solid A has a melting point of 158∘C158^\circ\text{C}158∘C. She concludes that Sample 4 is the purest sample because its melting range starts at the literature value of 158∘C158^\circ\text{C}158∘C.
Do the results support her conclusion? Explain your answer using evidence from the table and your knowledge of purity.