This is the unofficial mark scheme for:
Further addition science, unit 2 chemistry 3, C3
(be aware that there is two similar paper and the other one is chemistry 3, triple science. )
Reps will be appreciated but not necessary 😊
This will be updated regurlarly as i dont remember all the questions and answers. I will start by putting my answers so they might be wrong, but as soon as i know i will update it to correct answers☺
1.Carboxylic acids
Sentence with gaps to fill in:
a) (catalyst)acids,
(pleasant smelling compounds)ester
b) Completing the ethanol diagram: (sorry cant draw the bonds 😕but there is only single bonds)
H H
H C C O H
H H
(note: i can remmeber whether you had to draw ethanol or ethonoic acid, so can anyone confirm please)
c) Balancing-
C2H5OH + 3O2-----> 2CO2 +3H2O
2. Titrations
The method is:
1. use pipette to measure 50cm^2 of hydrochloric acid A and put it the conical flask
2. Put indicator (phenolphthalein) in the conical flask and mix it
3. put the conical flask on the white tile to see the colour change
4. Full the burette with soduim hydroxide up to the 0cm2 mark (making sure the tap is full)
5. Open the tap with one hand and swirl the conical flask with other hand to mix the alkali and acid together
6. Close the tap when the solution in the conical flask goes colourless
7. Work out how much acid was used by substracting the end reading of the burette from the initial reading.
8. repeat step 1-7
9. repeat step 1-8 but using the hydrochloric acid B as the acid in the conical flask
3.hardness of water
How boiling temporary hard water in kettles can reduce efficiency?
temporary hardness is caused by hydrogencarbonate which decomposes into calcium carbonate (a solid) called (lime)scale. this forms on the heating element of the kettle and acts as an insulator so less heat is transferred to the water, reducing efficiency. this means the water has to be heated longer, so more electricity used, and therefore more money used.
ion exchange resins to improve water quality
ion exchange column contain sodium resins. the sodium ions are exchanged for the calcium or magnesium ions (which caused the hardness). these are removed so hardness is removed too.
Table of results for compound testing:
White, the rest is no changes
Pottasium shows lilac flame and calcium red, why won't we able to see any of the colours if potassium and calcium were mixed?
any suggestions?
4. The periodic table
In 19th century, element were aranged in order of atomic mass
The elements are now aranged in order of atomic number. Which particles? electrons/protons
Highest boiling point: fluorine
Why reactivity increases as you down group 1, but decreases as you go down group 7?
Reactivity increases as you go down group 1 because they need to gain an electron. Shielding increases as you go down group 1 meaning the positive charge is felt less by the outer electron and it is therefore lost more easily
Rectivity decreases as you go down group 7 because they need to gain an electron. Shielding increases as you go down the group so it becomes harder for the nucleus to attract an electron.
5.bond energies
Energy change= 212
Reaction endothermic, why?
because the energy required to break the bond is greater than the energy released in making bonds so energy is absorbed.
Labelling energy level diagram (4 marks) :
The products are at higher energy level than the reactant
Line going up from the reactant line and then down to the product line.
Difference between reactant line and product line labelled energy change.
Activation energy- between reactant line to the highest energy reached
6. ammonia
Source of methane: crude oil, natural gas (any other suggestions, they will accept more than one answers btw)
higher yield of ammonia= 1000 atmospheres and 200 degrees
450 degrees, 200 atmospheres? 5 marks
decreasing the temperature encourage the forward reaction which is exothermic so more ammonia would be produced. however, too low temp means the reaction is too slow. therefore a compromise of 450 degrees is well suited.
increasing the pressure shifts the equilibrium to the side where there are fewer molecules so percentage yield of ammonia increases at high pressure. however too high pressure could break the plant/reactor so the reactor need to have thick walls which would be expensive to build. therefore, 200 atmosphere is a compromise; not too high to break the container but not too low so that here is enough percentage yield of ammonia
Mixture of gases, what hapens when they come out of the reactor? (3 marks)
Ammonia is condensed to be stored as a liquid
Hydrogen and nitrogen are recycled so that nothing is wasted (nearly 100% yield)
Any answers would be greatly appreciated. Feel free to correct me if my answers are wrong! Hope you did well
If anyone remembers how many marks a question was, please tell me so i can put it on. Thanks