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Two students each recrystallised a sample of the same organic solid and measured its melting point. The data-book value for the pure solid is 135 °C.
| Sample | Melting point range / °C |
|---|---|
| A | 122 to 130 |
| B | 134 to 136 |
Deduce which sample is purer, giving a reason.
Suggest one reason sample A may still be impure, and one way to improve its purity.