O-LevelChemistryStoichiometry5070/21 · May/June 2017 · Q910 Marks
Neon, argon, krypton and xenon are four of the noble gases. They are monatomic elements.
- (a)State a use of argon.[1]
- (b)What is meant by the term monatomic?[1]
- (c)Explain why the noble gases are very unreactive.[1]
- (d)(i)Chemists have discovered that some noble gases can form compounds. A 1.000g sample of one of these compounds contains 0.549 g of xenon, 0.134g of oxygen and 0.317 g of fluorine. Calculate the empirical formula of this compound. empirical formula ..............................................................[2]
- (d)(ii)What extra information is needed to deduce the molecular formula of this compound?[1]
- (e)Describe and explain how fractional distillation can be used to separate a mixture of neon, argon, krypton and xenon.[3]
- (f)A mixture of neon, argon, krypton and xenon can also be separated by diffusion. Explain why.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- B9(a) Light bulb / steel manufacture (1)
- B9(b) Exists as atoms (and not molecules) (1)
- B9(c) Atoms do not need to gain or lose electrons / has a stable electronic arrangement (1)
- B9(d)(i) element | xenon | oxygen | fluorine
- mass | 0.549 g | 0.134 g | 0.317 g
- moles | 0.00419 | 0.008375 | 0.0167
- Mole ratio | 1 | 2 | 4
- Correct moles (1)
- XeO2F4 (1)
- B9(d)(ii) Relative molecular mass / relative formula mass / molar mass (1)
- B9(e) Use liquid mixture / liquefy the mixture (1)
- Heat or boil the mixture (and collect fractions) (1)
- Idea that each fraction or gas has a different boiling point (1)
- B9(f) Each gas has a different relative atomic mass / atoms or molecules have different masses (1)
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