AQA AS Chemistry May 23rd 2019 UNOFFICIAL MARKSCHEMEWatch
Q. (a) Differentiate between a carboxylic acid and a ketone
– Add sodium carbonate, no visible change with the ketone but effervescence with carboxylic acid.
(b) Differentiate between an aldehyde and a ketone
– Tollen’s reagent, silver mirror with aldehyde and remains colourless with ketone.
Q. Enthalpy change for the reaction of C6H12 (?)
– -160 kJmol^-1
Q. Mechanism for Nucleophilic Substiution.
Q. Find the final temperature of the reaction.
– Somewhere in the 60s
Q. How much mass of CaO in kg was needed for the reaction.
– Around 5.4 x 10^9
Q. (a) Mechanism for Electrophilic Addition.
(b) Why does it produce more isomer E instead of F?
– Isomer E is formed from a secondary carbocation while F is from a primary carbocation. The secondary carbocation is more stable.
Q. (a) Show the formation of a Cl radical and another radical from the given compound.
(b) Show how it catalyses the breakdown of ozone.
•Cl O3 -> •ClO O2
•ClO O3 -> •Cl 2O2
Q. 6 marker on changing reaction conditions on the cost, yield, and rate.
– Catalyst does not change the yield but speeds up the reaction as it provides an alternate reaction path that lowers the activation energy. Increasing the temperature favours the backward reaction (in the question) and increases yield but increases the rate of reaction as more particles have greater energy, allowing for more frequent successful collisions. However, the cost would increase due to more energy being used. Increasing the pressure favours the forward reaction as well as increases the yield as the particles are closer together.
Q. Draw the skeletal formula of propandioic acid.
Q. Draw the apparatus used in the formation of propanal from propan-1-ol
Q. 6 marker on preparing a 250cm^3 standard solution of an acid.
– Measure the mass of an empty weighing boat and measure again after adding the acid. Use the difference between the masses to obtain the mass of the acid. In a beaker, add water and stir until the acid has dissolved. Transfer into a volumetric flask, with washings and add more water until the 250cm^3 mark is reached. Invert the flask at least 20 times to ensure complete mixing.
Q. Draw the hydrogen bonds formed between two molecules of methanol.
Q. (a) Volume of liquid butane (?)
– 1.5 x 10^4 cm^3
(b) Volume of butane gas
– 64.7 cm^3
I’ll add the other questions when I remember them
Please add this to mark scheme..i wrote 5.4*10^9 (I think)
(a) an initiation step for the CFC into the free radicals <-- 1 mark
(b) was this: •CL + O3 ->•CLO + O2
• CLO + 03 -> 2O2 + •CL <-- 2 mark
Also, how did people find it? To be honest, I found it fairly easy, easier than paper 1. Although from what I see, I'm worried about the grade boundaries going up alot because people seem to have to universally quite good
There was a 6 mark question on preparing 250cm3 of acid solution. I believe what you did was to measure beaker with a balance, then measure the mass of the acid and beaker with the balance. Then take the second reading away from the first to get accurate mass. Then add distilled water to the beaker and stir with a glass rod until dissolved. Then add that to a 250cm3 volumetric flask. Then wash the beaker with distilled water again and transfer to the volumetric flask to ensure that all dissolved acid is in the flask. Then add distilled water to the flask until it reaches the line, then state that you need to read from the bottom of the meniscus.
•reagent for ketone and carboxylic acid- sodium carbonate
see nothing for ketone and fizzing for the acid
reagent for ketone and aldehyde-Fehling’s solution/Tollen’s reagent
see nothing for ketone
solution goes red for aldehyde/silver mirror formed
•nucleophilic substitution, Br was replaced by CN
this formed propanenitrile
atom economy was 38.1% (or thereabouts)
•hess cycle gave a value of -160
different value due to heat loss to the surroundings/incomplete combustion
•C₈H₁₈ + 12.5O₂ ➝ 8CO₂ + 9H₂O
•1)a catalyst doesn’t affect the position of equilibrium but does affect the rate at which equilibrium is attained, faster rate of reaction by offering an alternative reaction pathway with a lower activation energy
2)forward reaction was exothermic so lower temperatures will increase the equilibrium yield as the system shifts to oppose the change, compromise is made however so a faster rate of reaction can be attained as higher temperatures increase the number of particles with activation energy leading to more frequent successful collisions, higher temperatures increase costs as more energy required
3)less molecules of gas on the right side so high pressures increase equilibrium yield as well as rate of reaction due to there being more particles within a given volume, however high pressures are expensive to maintain
•mass of CaO required- 5.4x10^9 kg
isomer E is formed via a secondary carbocation, which is more stable than the primary carbocation that isomer Z is formed from, hence meaning more of it is produced
•change in temperate (q=mcΔT) + initial temperature gave a final temperature of 62.7 degrees celsius
•mass required- 130mg
distillation apparatus drawn as the alcohol was oxidised to a aldehyde and not fully to a carboxylic acid as it would under reflux
CCl₂F₂ ➝ •CClF₂ + Cl•
Cl• + O₃ ➝ ClO• + O₂
ClO• + O₃ ➝ 2O₂ + Cl•
•forming a standard solution:
1)put the mass of the solid in a weighing boat and place on a mass balance, recording the mass
2)pour the solid into a conical flask and reweigh the boat
3)mass of the solid=initial mass-final mass
4)add distilled water to the conical flask until all of the solid has dissolved, and use a stirring rod to ensure this
5)pour the contents into a volumetric flask, using distilled water on the conical flask and stirring rod to ensure that all of the contents have entered
6)fill the flask up to 250cm^3 with distilled water, adding it drop by drop using a pipette towards the end-stop when the bottom of the meniscus lies on the line
7)place a stopper on the flask and invert multiple times
•hydrogen bonding (lone pairs on the oxygen)
bond angle of 104.5 due to lone pairs on the oxygen repelling more than bonding pairs, thus giving it a bent shape and reducing the angle from 109.5
•volume of gas was 15000cm^3
volume of liquid was 65 (ish) cm^3
expansion factor of around 230