A-level Chemistry Paper 2 2020
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Define the term overall order of reaction
All the orders added/ sum of the (individual) orders
State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.
all have the same Mr
Suggest a suitable piece of apparatus to measure out the ethanoic anhydride in step 5.
burette
Suggest two ways in which the melting point of the crude aspirin collected in step 9 would differ from the melting point of pure aspirin
wider range of melting points lower value
Describe two important precautions when heating the mixture of ethanol and crude aspirin. 78 bp
hot water bath ethanol is flammable heat below bp
Describe one difference in appearance you would expect to see between these two solid samples.
Pure product will have (larger) crystals / needle-like crystals / lighter in colour
A compound is usually mixed with Si(CH3)4 and either CCl4 or CDCl3 before recording the compound’s 1 H NMR spectrum. State why Si(CH3)4, CCl4 and CDCl3 are used in 1 H NMR spectroscopy. Explain how their properties make them suitable for use in 1 H NMR spectroscopy.
TMS is Si(CH3)4 and it is used as a reference which sets a peak at 0ppm inert so unlikely to react with compounds like CDCL3 of CCL4 Volatile so easy to remove CCL4 is non polar so its good for non-polar compounds CDCL3 is polar so its good for polar compounds both have no H atoms so give no signals
Suggest why an expression for K can be written without the concentration of water.
[H2O] / conc of water is (effectively) constant
When an excess of water is added to ethanal a similar nucleophilic addition reaction occurs. CH3CHO(aq) + H2O(l) ⇌ CH3CH(OH)2(aq) Suggest why this reaction is slower than the reaction in Question 09.5.
M1 C in C=O is less δ+ / less electron deficient M2 CH3 has a (positive) inductive effect M3 So higher Ea