You are Here: Home

# AS Chemistry- helping each other out! watch

1. But isn't the mass of water supposed to be in kg? 25cm(3) = 25g = 0.025kg? But thanks for your help!

Posted from TSR Mobile
2. Thanks (:

Posted from TSR Mobile
3. (Original post by ohnanailikenanas)
But isn't the mass of water supposed to be in kg? 25cm(3) = 25g = 0.025kg? But thanks for your help!

Posted from TSR Mobile
what do you mean? In the working out moles equation? if it gives you the concentration and volume, you use that equation
if it gives you the grams of something you use moles=mass/mr equation and the mass is in grams
4. Yeah, sorry! I read over it and I understand it now! Just forget what I said earlier! Thank you so much for your help!

Posted from TSR Mobile
5. Hiya,,, does anyone have any saltars B chemistry resources/ notes that i can use?
thanks for any help...
6. (Original post by mismash)
Hiya,,, does anyone have any saltars B chemistry resources/ notes that i can use?
thanks for any help...

http://www.4college.co.uk

Really good for ocr b
Posted from TSR Mobile
7. (Original post by thegreatimposter)
http://www.4college.co.uk

really good for ocr b
posted from tsr mobile
thank you very much for the link
8. Can someone please give me a step by step guideline on how to predict the shapes and bond angles in molecules and ions? I find this really difficult and the book only confuses me
9. Anyone have tips on how to revise for Chemistry?
10. (Original post by Super199)
Anyone have tips on how to revise for Chemistry?
11. (Original post by frozo123)
Do you do like a chapter at a time or? I'm with AQA and there are quite a few chapters and doing a chapter a day or so will be rather time consuming.
12. (Original post by lukejoshjames)
Mr means molecular mass, which is defined as the mass per mole of a molecule. If you numbers within the empirical formula itself, for example in MgCl2, then you would add the Mr of Magnesium to twice the Mr of Chlorine, and that would give the you the Mr of MgCl2.
However, if there is a number before the empirical formula itself, for example 2MgCl2, that is the same as 2(MgCl2), which is 2 moles of MgCl2. As Mr is mass per mole, finding the mass of 2 moles of the substance would be incorrect unless you divided that by whatever number of moles there are of the substance.
In short: every single atom in a molecule has to be count in calculating the molecular mass. Example by myself: FeO3. To get the molecular mass, the mass of one iron atom must be added to the mass of three oxygen atoms.

Makes sense, as a molecule consists of atoms.
13. (Original post by Super199)
Do you do like a chapter at a time or? I'm with AQA and there are quite a few chapters and doing a chapter a day or so will be rather time consuming.
I'm with edexcel and I assume all the exam boards are pretty much the same anyway, heard edexcel and salters B are the hardest though.
Hm not really?
I think if you thoroughly revise, you can get through 3/4 of the chapters a day. I read the whole book a couple days ago over the two days, guess it took me 4 hours to understand 90% of it.

Just do questions from the book, and past papers, read the markscheme, so you don't make similar mistakes again.
14. For the 'Green Chemistry' topic of the Unit 2 Exam in AS OCR A, how much detail do we need to go into? Im a little lost as to whether we need to know lots of examples etc.

Thanks

Posted from TSR Mobile
15. OCR A
16. (Original post by jerseyalevel)
For the 'Green Chemistry' topic of the Unit 2 Exam in AS OCR A, how much detail do we need to go into? Im a little lost as to whether we need to know lots of examples etc.

Thanks

Posted from TSR Mobile
In past papers, examples have been of the type e.g.: "Give 2 ways of disposing of waste polymers" to which you could reply "combustion of plastics to give energy, and 'sorting+moulding"

and the subtly different question type e.g. "give 2 ways chemists have developed new techniques to reduce waste" to which you could reply "developing photodegradable polymers and developing use as chemical feedstock in cracking"

look at past papers for examples of how much detail you need to go into, but just to be safe, learn 1 level of detail beyond this
17. Posted from TSR Mobile
Ugh,I have to revise Green chemistry over the two week break. ozone layer calculations are a nightmare.
18. Can someone explain the displacement reactions for the halogens. Is the reason why bromine cannot displace chlorine due to chlorine being more reactive than it. Also when bromine displaces say potassium iodide do you get an orange or brown solution?
19. Does anyone know a resource with model answers to typical past paper questions?
20. (Original post by Super199)
Can someone explain the displacement reactions for the halogens. Is the reason why bromine cannot displace chlorine due to chlorine being more reactive than it. Also when bromine displaces say potassium iodide do you get an orange or brown solution?
the oxidising ability decreases as you go down the halogens, chlorine is a smaller atom than bromine, which means that when it oxidises the bromide ion the incoming electron from that ion feels an overall stronger attraction so the electron would be pulled more strongly to the chlorine forming the chloride ion. So you'd get orange bromine.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: July 24, 2017
Today on TSR

### The most controversial member on TSR?

Who do you think it is...

### Uni strikes! How do they affect you?

Discussions on TSR

• Latest
Poll
Discussions on TSR

• Latest

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE