liquid cobalt(II) chloride paper boiling point / °C A stays blue 65 B turns pink 100 C turns pink 108 D stays blue 100 Four colourless liquids were each tes...
Question 1 Report
| liquid | cobalt(II) chloride paper | boiling point / °C |
|---|---|---|
| A | stays blue | 65 |
| B | turns pink | 100 |
| C | turns pink | 108 |
| D | stays blue | 100 |
Four colourless liquids were each tested with cobalt(II) chloride paper and their boiling points measured, as shown. A liquid that is pure water turns the paper pink and boils at exactly 100 °C. Use the results to identify the pure water.
Answer Details
Two conditions have to be met at once, so work through the table using both columns. Turning cobalt(II) chloride paper pink shows that water is present, which rules out both liquids that leave the paper blue. That leaves the two liquids turning the paper pink.
Of those, one boils at 108 °C, which is above the fixed boiling point of water and shows a dissolved solute raising the boiling point, so it is a solution rather than pure water. The other boils at exactly 100 °C and turns the paper pink, so the pure water is liquid B.
The trap is the liquid that boils at 100 °C but leaves the paper blue: a correct boiling point alone is not enough when the water test fails.
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