Purity, Formulations and Chromatography Quiz
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5 questions, one answer each
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1. Which of the following best describes a pure substance?
- A. A single element or compound not mixed with any other substance
- B. A mixture of two or more elements that has constant properties
- C. Any substance that appears uniform to the naked eye
- D. A compound that has been filtered to remove impurities
2. What is a formulation?
- A. A pure chemical compound manufactured in a laboratory
- B. A mixture designed to have specific useful properties for a particular purpose
- C. Any substance that contains more than one element
- D. A chemical that has been purified using chromatography
3. In paper chromatography, a substance travels 6 cm up the paper whilst the solvent travels 10 cm. Calculate the Rf value.
- A. 0.6
- B. 1.67
- C. 0.4
- D. 4.0
4. Two substances have Rf values of 0.35 and 0.52 respectively when tested using the same solvent and paper. What does this tell you?
- A. Both substances are pure and identical
- B. The substances are different and have different solubilities in the solvent
- C. The substance with the higher Rf value is more pure
- D. The solvent used was unsuitable for this separation
5. A student tests a white powder and finds it melts at different temperatures between 60 °C and 80 °C. A pure sample of substance X melts at exactly 72 °C. What can be concluded?
- A. The white powder is a pure substance and is definitely substance X
- B. The white powder is likely a mixture because a pure substance has one specific melting point, so it cannot be substance X
- C. The white powder must contain substance X with some impurities
- D. The melting point test cannot be used to determine purity