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AQA GCSE Chemistry - C2 & C3 (14th May 2015) watch

1. (Original post by liv1111)
• can someone help me with electrolysis... just a simple method please x
*Electrolysis separates ionic compounds using electricity*

The circuit is comprised of a battery, two electrodes and the electrolyte (basically a beaker with the compound you want to separate in)

Positive metal ions are attracted to the negative anode. They gain electrons to form metal atoms. This is called REDUCTION.

Negatively charged ions are attracted to the positive anode where they lose electrons, often producing oxygen bubbles. This is called OXIDATION.

I'd say the basic key points to remember are:
- Ionic compound MUST be molten or in a solution for electrolysis to work
- metals ions -> negative electrode
- non metals -> positive electrode
- OIL RIG is a great memory tool (Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons))

I think that just about covers the basics, hope that helps!
There are some good videos on YouTube if seeing something visual will help. Most of them are condensed into 8-10 minute lessons.
2. (Original post by harryleavey)
1. You will be given 2 (possibly 3) elements
e.g Sodium (Na) and Sulphur (S) and Oxygen (O)

2. You will be given the mass or the percentage - they both work the same way
e.g 4.6g of Na and 3.2g of S and 6.4g of O

3. You need to get the Mr of each element by looking at the top number on the periodic table.
In this case Na is 23 and S is 33 and O is 16

4. Divide the percentage or mass of each by its own Mr value
4.6/23 = 0.2 and 3.2/33 = 0.1 and 6.4/16 = 0.4

5. Divide this result by the lowest result just obtained.
So the lowest result was 0.1 - So all 3 are divided by 0.1
0.2/0.1 = 2 and 0.1/0.1 = 1 and 0.4/0.1 = 4

6. Put these 3 values in front of the symbols
Na2 S1 O4
= Na2SO4
I understand all of this except mass/percentage.. How did you get 4.6 (Na), 3.2 (S) and 6.4 (O)..

Can you tell me how?
3. What topics do you think are going to come up tomorrow on the Chemistry exam?
4. (Original post by Samistrawberry)
Ahh I see thank you!

Do you think we could get a 5 marker on paper chromatography? They could ask something like describe how to identify additives using paper chromatography?
It is possible but unlikely because similar questions have come up twice before.
5. (Original post by RotomGuy)
Lonsdale Revision Plus. It's not a typo either, there's a little diagram with a pile of impurities gathering below the cathode.
Oh, that's weird! Mine's the CGP AQA GCSE chemistry, mine definitely says pure plating metal.
6. Guys, could you help me with acid reacting with metals​ and all these tests
7. (Original post by pollyy)
1. Use a pipette to add (e.g 250cm^3) of the solution of known concentration into conical flask. A conical flask is used to reduce risk of spillage when swirling.

2. Add indicator (phenolphthalein or methyl orange, but I don't think you need to know this) to the conical flask, and place on a white tile so that a colour change can be easily observed when neutralisation occurs. Ensure not to use universal indicator, as it gives a gradual colour change when a sudden one is needed here.

3. Fill the burette with the other solution, which you don't know the volume of. Clamp burette above flask.

4. Dispense the solution in the burette into the flask, dropwise (particularly near neutralisation). Swirl between additions.

5. When a colour change is observed, record the volume of the substance in the burette that was required for neutralisation.

6. Repeat the whole thing for more readings to find a mean average. Ensure the same person judges colour change as result can be subjective.

I think that's everything!
Thank you soo much! You're a star!!
8. (Original post by RotomGuy)
Can someone help with an ideal list of points for a 6 mark question on LD, HD, thermosetting/softening polymers? I can't recall what the first two are and I can't think how to write 6 marks worth of polymer structure.

I'm not 100% sure but I'd include:
- Properties of polymers depend on the monomer it's made from and the conditions the reaction was carried out in.
- Low density polyethene and high density polyethene are made using different catalysts and different reaction conditions.
- HD polyethene is stronger and had a higher softening temperature than LD -polyethene
- Thermosoftening poylmers are made of individual polymer chains tangled together. weak intermolecular forces of attraction between the chains are easily overcome by heat, meaning it softens when heated so can be melted down and remoulded.
- Thermosetting polymers have covalent cross links between chains that hold the polymer chains in position, meaning they don't soften when heated.
9. (Original post by spnlove)
For the other two:

Making soluble salt from acid + alkali

2. Add alkali until indicator changes colour and record how much alkali was used
3. Repeat this using exactly same volumes of alkali and acid but without the indicator so that the salt isn't contaminated
4. Then evaporate the water to concetrate the solution
5. Leave the rest to evaporate slowly (crystallisation)

Making insoluble salt - Precipitation reaction

1. Mix two solutions containing ions you need (i.e. for lead chloride you could mix lead nitrate solution and sodium chloride solution)
2. Once precipitation has occurred (it will leave a solid), you just filter the solution
3. Wash and dry precipitate on filter paper

If anyone has any corrections for those please tell me cause I find this stuff really hard to remember!
Thank you so much! I've never quite been able to get my head around these, you're a life saver
10. There are 2 types we need to know:
Brine is NaCl. it is dissolved in water to form Na+ and Cl- ions along with the H+ and OH- ions from the water. the least reactive goes to the electrodes first so at the negaitve electrode two H+ ions form H2 gas. At the positive electrode, two Cl- ions form Cl2 gas. this leaves NaOH in the beaker. H2 gas is used in food, chlorine is used to clean swimming pools and NaOH is used in soaps and paper.
The electrolysis is Aluminium oxide is slightly harder. it is melted using cryolite to bring the melting point down to 1000 degrees to save energy and consequently money. Th positive anode is made of graphite and so when the O2- ions loose their electrons,they combine with the carbon to produce CO2 gas. the Al3+ goes to the negative cathode with surrounds the outside of the container! and so forms pure Aluminium, which can then be used for transport, construction or packaging etc.

Hope this has helped and not 100% sure so feel free to correct it anyone
11. Does anyone know the reason for electroplating?
12. Hopefully there will be some calculations on the papers.
13. (Original post by morrissies)
*Electrolysis separates ionic compounds using electricity*

The circuit is comprised of a battery, two electrodes and the electrolyte (basically a beaker with the compound you want to separate in)

Positive metal ions are attracted to the negative anode. They gain electrons to form metal atoms. This is called REDUCTION.

Negatively charged ions are attracted to the positive anode where they lose electrons, often producing oxygen bubbles. This is called OXIDATION.

I'd say the basic key points to remember are:
- Ionic compound MUST be molten or in a solution for electrolysis to work
- metals ions -> negative electrode
- non metals -> positive electrode
- OIL RIG is a great memory tool (Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons))

I think that just about covers the basics, hope that helps!
There are some good videos on YouTube if seeing something visual will help. Most of them are condensed into 8-10 minute lessons.
omg!!! thank you so much
Actually just saved my life here, thanks!!! Anyone got standard 6 points for a Q on soluble and insoluble salts? Thank you!!!
Your'e welcome!
Making soluble salts:
1) Acid + Alkali = Salt + Water (Neutralization reaction)
2) Acid + Metal = Salt + Hydrogen
3) Acid + Insoluble base = Salt + Water

Making insoluble salts:
Add two solutions to each other to gain desired ions together.
i.e if you wanted lead iodide, you could add lead nitrate to potassium iodide to from lead iodide and potassium nitrate. This is effectively a displacement reaction
Insoluble Salts can be used for treating effluent, which is waste from factories that could harm to the environment.
15. Good luck everyone, Hopefully tommorow the thread won't be full of angry people like in the biology thread ;P
16. Can anyone help me out with electroplating? I know the basics but not enough for a 6 mark question on it :/
17. anyone have any predictions of what will come up in tomorrows aaa igcse chemistry exam?
18. (Original post by Studentz001)
Thank you soo much! You're a star!!
Haha it's okay! Good luck tomorrow and let me know if there's anything else!
19. (Original post by Studentz001)
Does anyone know the reason for electroplating?
you might coat a metal in something for that somethings desirable properties or just for cost e.g. coat a cheap metal in a thin layer of a precious one rather than making the whole thing out of the precious one
20. (Original post by TheTruthTeller)
Good luck everyone, Hopefully tommorow the thread won't be full of angry people like in the biology thread ;P
It will be, it's inevitable. At least there are no magnification questions on a chemistry test.

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