A student is separating some mixtures.
She wants to obtain pure, dry sand from a mixture of sand and sodium chloride (common salt). She adds water to the mixture to dissolve the salt, and then immediately evaporates the water to dryness.
Explain why her method does not work and describe the correct method she should use.
The student wants to separate a mixture of two miscible liquids: hexane and octane.
The boiling points of the two liquids are:
| Liquid | Boiling point (∘C^{\circ}\text{C}∘C) |
|---|---|
| Hexane | 69 |
| Octane | 126 |
Which separation technique should she use?
Explain how this method works to separate these two liquids.
The student separates two solid substances. She wants to check if they are chemically pure.
What is meant by a pure substance in chemistry?
The student measures the melting points of four different samples of solid salicylic acid.
Look at her results:
| Sample | Melting point (∘C^{\circ}\text{C}∘C) |
|---|---|
| W | 155 |
| X | 150–154 |
| Y | 159 |
| Z | 160–162 |
She knows that a pure sample of salicylic acid has a melting point of 159∘C159^{\circ}\text{C}159∘C.
She concludes that sample Z is the purest sample because it has the highest melting point.
Do the results support her conclusion?
Explain your answer using evidence from the table.