A level aqa chemistry paper 3 2017 helpWatch
For 3.8, I was quite confused. I dont understand what purification methods you know to use? Why can't you use a separating funnel (as the product is insoluble in water)? Also, how do you know the order of purification methods to take - is it always the case that you do washing and drying last?
For 4.5 and 4.6, I didn't really understand what to do. Can someone please explain?
For 2.5, I dont really understand how you get different skeletal formulas for but-1-ene and but-2-ene?
For 2.8, it says the yellow solid is sulphur but where does this come from - I get that so2 is produced but where does the s8 come into it? I know this isn't in the question but is HI observations purple vapours?
Finally, for 12 on the multiple choice, how is the answer c? Surely it could be d too? For 17, how surely it could be b and c, yet the ms says only b? surly in both the oxidation state of v as increased by 1? For q25, couldn't the anser be c or d? wouldn't both compounds result in the formation of the same polymer?
Any help would be greatly appreciated. many thanks
4.5: pKa = pH at half equivalence, so you do -log(Ka) to get pH
4.6: plot values from 4.5 and 4.4, graph must go through both these points and because it starts out as a weak acid there is a dip that stabilises as it goes through the phase where it acts as a buffer solutions
2.5: Different skeletal formulas for but-2-ene because you have E-but-2-ene and Z-but-2-ene
2.8: S8 is solid sulfur and can be produced in these reactions, we don't have to know the equation for this as far as I'm aware, just know it's one of the products, its one of those facts you just have to know )
12: I agree with you, I've got no idea how they can tell between the two
17: Technically B does work, but it's not the reaction of the contact process, that is SO2 + 0.5O2 --> SO3
25: It's C because acyl chlorides react with alcohols vigorously of their own accord, D is a haloalkane and won't react spontaneously with a carboxyl group. Tbh I chose it because we've covered acyl chloride reactions with alcohols but not carboxylic acids with halogenalkanes.
Hope this helps, good luck for Wednesday