How do you check the purity of a collected solvent?

• A. By testing its melting point
• B. By testing its boiling point
• C. By testing its melting or boiling points
• D. By tasting it

Answer: (C)

Purity shows up in how a substance changes state. A pure solid has a sharp melting point at a specific temperature, while impurities make it melt over a range and at a lower temperature. A pure liquid boils at a single temperature at a given pressure; impurities raise the boiling point and often broaden the boiling range. So to check the purity of a collected solvent, you can test its melting point if it’s a solid or its boiling point if it’s a liquid and compare the result with the known values. Using either (melting or boiling points) covers both possibilities, which is why this option is best. Tasting is unsafe and unreliable, so it isn’t appropriate.