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# A-level Chemistry Revision Squad! watch

1. (Original post by FemaleBo55)
What is the uncertainty for a 250cm3 grade B volumetric flask and a 50cm3 grade B volumetric flask? Lol, I tried looking online I couldn't find it; it's either that I'm blind LOL or that it isn't necessary??
is it not 0.05 for 50 and 0.5 for 250????
2. Why is that the quantity of reactant determines the energy change i.e. the amount of energy given out out or taken in during a reaction, as well as other factors?
3. Anyone know any good resources for mass spec? (AQA A2)
4. (Original post by SANTR)
Why is that the quantity of reactant determines the energy change i.e. the amount of energy given out out or taken in during a reaction, as well as other factors?
Its just like anything else. When you eat a chocloate bar the amoujt of energy on the packet given is the energy per chocolate bar, so if you eat two chocolate bars you get twice the energy. Similarly all the enthalpy changes are defined for a given quantity of the substance e.g per mole. Therefore if you have a different number of moles then, in the same way that the amount of energy you take in depends on how many mars bars you eat, the energy given out/taken in will also be different
5. (Original post by Manexopi)
Anyone know any good resources for mass spec? (AQA A2)
6. (Original post by samb1234)
Its just like anything else. When you eat a chocloate bar the amoujt of energy on the packet given is the energy per chocolate bar, so if you eat two chocolate bars you get twice the energy. Similarly all the enthalpy changes are defined for a given quantity of the substance e.g per mole. Therefore if you have a different number of moles then, in the same way that the amount of energy you take in depends on how many mars bars you eat, the energy given out/taken in will also be different
Would I be correct in saying that, the larger the quantity of reactant, the more bonds there are and therefore more energy has to be taken in to breaks bonds?
7. (Original post by SANTR)
Would I be correct in saying that, the larger the quantity of reactant, the more bonds there are and therefore more energy has to be taken in to breaks bonds?
Theres more of everything. Enthaloy changes can be calculated by various means e.g. you might have enthalpues of solution, bond enthalpies etc etc. It doesnt matter which one they are all defined for a given quantity of reactant so if that reactant is a different quantity than the value of that enthalpy change is different
8. (Original post by Manexopi)
I've already read that and I still don't really get it but thanks anyways. Seems like this topic is just trial and error then.
What don't you get?
9. (Original post by samb1234)
What don't you get?
How you know what the fragment is but it appears you just play around abit with mass numbers and you'll get it eventually?
10. Does anyone want a Skype revision session? Exam board ocr
11. (Original post by Manexopi)
How you know what the fragment is but it appears you just play around abit with mass numbers and you'll get it eventually?
It is a bit of trial and error but normally things will form fragments that are easy to predict. E.g. if you had propane the most likely fragments would be that the ch3 group on the end break off so you get a ch3 fragment and a c2h5 fragment
12. Anyone have any tips for getting an A? So far I've done all the past papers from my first unit with my exam board (not sure if this was a good idea) and now I am going over AS and topics I have struggled with. But my grades fluctuate from an a* in one paper and then a C in another paper. Not sure where I'm going wrong?
13. The reaction between Peroxodisulphate ion and Iodide ions: a possible mechanism when the iodide ions approach the perxodisulphate and it formsn an intermediate with it then another one arrives and form a bond with the bond of perxodosiulphate ions too. My question is due to what reason does the peroxodisulphate ion bond break? is it because the Iodide ions together have higher stronger van der waals force of attraction than the bondof peroxodisulphate??
Anyone have any tips for getting an A? So far I've done all the past papers from my first unit with my exam board (not sure if this was a good idea) and now I am going over AS and topics I have struggled with. But my grades fluctuate from an a* in one paper and then a C in another paper. Not sure where I'm going wrong?
Learn all of the content thoroughly before you do any more past papers. Use your specification to ensure you know literally everything you need to, and then you can use past papers to iron out any small issues rather than doing them and every time realising you dont know a whole topic.
15. (Original post by samb1234)
Learn all of the content thoroughly before you do any more past papers. Use your specification to ensure you know literally everything you need to, and then you can use past papers to iron out any small issues rather than doing them and every time realising you dont know a whole topic.
At this stage, in your opinion, do you think that one should start past papers if their understanding of the topics isn't entirely there yet or is it better to thoroughly learn all the content but this would mean leaving the past papers quite close to the exams?
16. (Original post by AKRYL)
At this stage, in your opinion, do you think that one should start past papers if their understanding of the topics isn't entirely there yet or is it better to thoroughly learn all the content but this would mean leaving the past papers quite close to the exams?
Learn content, in all honesty if you learn the content properly you wouldn't have to do past papers to get an A. In my opinion knowing the content extremely well is what's going to move you up whole grades, whereas past papers are just there to help you refine exam technique and gain an extra few marks here and there
17. (Original post by AKRYL)
At this stage, in your opinion, do you think that one should start past papers if their understanding of the topics isn't entirely there yet or is it better to thoroughly learn all the content but this would mean leaving the past papers quite close to the exams?
It's best to thoroughly know the topics before doing past papers. But by doing past papers it really gives you an idea what grade your on so you may want to have a go at one. However I wouldn't advice doing all the past papers towards the end. Try to learn the content quickly and test your knowledge with a few past papers soon.
18. hey , how are people revising reagents & conditions??
19. (Original post by flynnmoore 1597)
hey , how are people revising reagents & conditions??
I'm learning them one at a time so I don't have my brain exploding xD Also, I'm doing them by topic instead of learning them all together (learning a whole topic before moving onto the next) so I don't get confused and can associate the reaction I'm being asked about to a topic and can work out the reagents from there. Hopefully this made some sense (:
20. Anyone else here doing A2?

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