A sample of canola oil is mainly the unsaturated fat Z\text{Z}Z mixed with a small amount of inert impurity. The unsaturated fat Z\text{Z}Z has the molecular formula C57H102O6\text{C}_{57}\text{H}_{102}\text{O}_6C57H102O6 (Mr=882M_r = 882Mr=882) and contains 4 carbon-carbon double bonds per molecule.
The amount of Z\text{Z}Z is determined using the following procedure:
A suitable target titre for the titration is 32.0 cm3 of 0.020 mol dm-3 Br2(aq)\text{Br}_2(\text{aq})Br2(aq).
Justify why a much smaller target titre would not be appropriate.
Calculate the amount, in moles, of bromine in this target titre.
Calculate a suitable mass of canola oil to transfer to the volumetric flask using your answer to Part 1 and the structure of Z\text{Z}Z. Assume that the canola oil contains 80.0% of Z\text{Z}Z by mass. (If you were unable to calculate the amount of bromine in the target titre, you should assume it is 6.0 × 10-4 mol. This is not the correct amount.)
The canola oil solution is prepared using this method:
Suggest an extra step to ensure that the mass of canola oil in the solution is recorded accurately. Justify your suggestion.
State the reason for inverting the flask several times.
A sample of the canola oil was dissolved in methanol and analysed using electrospray ionisation mass spectrometry. Each molecule gained a hydrogen ion (H+\text{H}^+H+) during ionisation. The spectrum showed a peak for an ion with m/z=253m/z = 253m/z=253 formed from an impurity in the canola oil. This ion was formed from a compound with the empirical formula C5H8O\text{C}_5\text{H}_8\text{O}C5H8O. Deduce the molecular formula of this compound, showing your working.
79 exam-style questions on AQA A Level Chemistry Amount of substance, covering Relative atomic mass and relative molecular mass, The mole and the Avogadro constant, The ideal gas equation, Empirical and molecular formula, and Balanced equations and associated calculations. Each one has a worked solution and a mark scheme showing where the marks go.