Methods of Separating & Purifying Substances Quiz
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5 questions, one answer each
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1. What is the chemistry definition of a pure substance?
- A. A substance from a natural source
- B. A single element or compound not mixed with any other substance
- C. Any liquid that is colourless
- D. A substance that dissolves completely in water
2. Which technique should be used to separate salt (dissolved) from water when you want to keep the salt?
- A. Filtration
- B. Crystallisation
- C. Paper chromatography
- D. Simple distillation
3. A student measures the melting point of a white solid and finds it melts gradually between 110°C and 118°C. What does this suggest?
- A. The substance is pure
- B. The substance is a mixture or impure
- C. The substance is a gas at room temperature
- D. The measurement is irrelevant to purity
4. How is sea water made potable, and why can't the standard waste-water method be used?
- A. By chlorination only, because it removes salt
- B. By distillation, because sedimentation/filtration/chlorination cannot remove dissolved salts
- C. By filtration only, because salt is a solid
- D. By crystallisation, because salt crystallises out naturally
5. A student runs a chromatogram of an unknown dye alongside three reference dyes, A, B and C. The unknown spot travels 4.2 cm and the solvent front travels 6.0 cm. Reference dye B has an Rf value of 0.70. Is the unknown likely to be dye B?
- A. No, because Rf values cannot be compared between substances
- B. Yes, because the unknown's Rf value (4.2/6.0 = 0.70) matches dye B's Rf value
- C. No, because the unknown travelled further than the solvent
- D. Yes, but only if the colours are different