Simple differences between mixtures and compounds
3 marks · EasyThe table below shows the melting points of three samples. Use the data to answer the questions.
| Sample | Melting point (°C) |
|---|---|
| A | 801 |
| B | 112–130 |
| C | 0 |
Which sample is a pure substance? Explain your answer.
State what the melting range in sample B tells you about its purity.
The boiling point of sample C is 100°C. Is C most likely a pure substance or a mixture? Give a reason.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Sample A
(b) Sample B is not pure / it is a mixture
(c) Pure substance, because it has a sharp melting and boiling point
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies sample A as pure because it has a sharp melting point.
B1 (b) · 1 mark · States that sample B is not pure or is a mixture, because it melts over a range.
B1 (c) · 1 mark · States sample C is a pure substance (water) because it has a sharp melting and boiling point.
Worked solution
a) Sample A is pure because it has a sharp melting point (801°C) instead of a range.
b) The melting range of sample B (112–130°C) shows it is a mixture, not pure.
c) Sample C is most likely a pure substance because it has both a sharp melting point (0°C) and boiling point (100°C).