A-level Chemistry Revision Squad!

Scroll to see replies

Hey, congrats on the A*, I would like to ask, whats the best way to revise for chemistry.
I havent started yet and i am about 30 days from from first exams, could you suggest something.

Well I had the old spec so my advice may be a bit out dated.

I just tbh revised my notes for around a week. I would read them, then write them back after a few hours to make sure I really learnt them.

Then I would do all the past papers, including every single old spec paper. From 2000-2013.

Thats honestly the best advice I can give sorry, I know its really short but honestly thats it. Make sure you know the material and practice exam style questions, if you can do that you will get an A* no problem.

One tip: Chemistry isnt biology. Memorising the content wont get you far, you did to really understand everything you're learning and dont just simply remember it. Exam boards test chemistry has a subject where you apply your knowledge and if you're simply just remembering things you wont be able to apply it to new situations.

Reply 321

Science_help

Original post by Cobalt_

Thank you for this soo much

Reply 322

Cobalt_

Original post by Science_help

Thank you for this soo much

Np, just put the work in and you'll get your A*.

If I got an A*, anyone can.

Reply 323

Science_help

Original post by Cobalt_

Np, just put the work in and you'll get your A*.

If I got an A*, anyone can.

well i am currenlty in year 12, so only can get an A, but all year ive been geting around 90-95%, and so i really want atleast 95% ums in chem AS

Reply 324

TheGreatPumpkin

Help please.
Q)... prepares 250cm3 of a 0.0800moldm-3 a solution of borax water, calculate the mass of borax (Na2B4O7.10H2O) to make this solution
A) Molar mass of borax = 381.2 (g mol–1) 
Correctly calculates the mass of borax in 1000 cm3 =0.0800 x 381.2= 30.496 g OR 30.50 g OR 30.5g
Correctly calculates the mass of borax in 250 cm3 =30.496/4= 7.624 g OR 7.62 g

How do you know it's 1000 cm3?

Reply 325

chzm

can someone explain something to me..
In the titration where you add potassium manganate(VII) to an unknown conc of a reducing agent (e.g. iron, zinc, or Fe2+)
why is the end point of the reaction indicated by a colour change of colourless to pink?
Surely if you're adding manganate (VII) ions to Fe2+ ions, it will be reduced to Mn2+.. which is colourless?
Why do you get a purple colour in the conical flask?

Reply 326

MedSchoolDreams

Original post by RMNDK

There are some mistakes in your equation of Co²⁺ with NH₃.
You also might want to give the colour of [Co(H₂O)₆]²⁺before it is oxidised by oxygen.

How come you haven't included the equation of Fe³⁺ with excess OH^-?
The precipitate will dissolve in concentrated NaOH.

I'll relook through it, sorry about the mistakes. I will repost the altered version

Reply 327

RMNDK

Original post by chzm

I wouldn't say purple, the end-point is the first hint of a pink tinge colour.

The reason why it's colourless to pink is because exactly what you said.
If you add Mn⁷⁺ to Fe²⁺, they will be reduced to Mn²⁺which is colourless.

As I keep adding and adding the Mn⁷⁺, all the Fe²⁺ will eventually become oxidised to Fe³⁺.

There is a single moment when I have fully oxidised all the Fe²⁺ in the conical flask, and so at that moment, there is no more Fe^2+.

Thus, the instant I add more Mn⁷⁺, it's going to remain as Mn⁷⁺ because there's nothing to oxidise. Thus we get this pink tinge colour. Add some more and we get that intense purple colour.

Unless you wanted to use some sort of indicator which changes colour around the neutralisation point, you would look for this colour change. And we tend not to because it is a prominent change.

Reply 328

LThomas694

Original post by chzm

Because the Fe2+ ions have been used up at the end point, so there are some purple Mn7+ ions which can't be oxidised to colourless Mn2+ ions so the solution turns pink

Reply 329

username986184

Original post by LThomas694

Because the Fe2+ ions have been used up at the end point, so there are some purple Mn7+ ions which can't be reduced to colourless Mn2+ ions so the solution turns pink

OILRIG

Reply 330

LThomas694

Original post by TeachChemistry

OILRIG

Sorry if I've messed something up there but I swear that's right? In the overall redox equation:
MnO4- + 8H+ + 5Fe2+ --> Mn2+ + 5Fe3+ + 4H2O
Mn7+ ions are reduced to Mn2+ because reduction is a gain of electrons and a decrease in oxidation number, and Fe2+ ions are oxidised to Fe3+ ions because oxidation is a loss of electrons and an increase in oxidation number?
At the end point all of the Fe2+ ions have been oxidised to Fe3+ so there aren't any Fe2+ ions left to reduce the Mn7+ ions to Mn2+ so the solution turns pink since Mn7+ ions are purple?

Reply 331

username986184

Original post by LThomas694

That's right but it's not what you wrote initially.

Reply 332

NimbleNeil

I'm doing edexcel A2 Chemistry, Part of our specification says :" Demonstrate understanding of the term ' dynamic equillibrium' as applied to states of matter, solutions and chemical reactions".

I am perfectly okay with the understanding of it in terms of chemical reactions but know nothing of its application to "States of matter and solutions". :frown:

(((((

Reply 333

Jassy16

What volume of oxygen, in cm³, would be required for 0.1 moles of cyclohexane to undergo complete combustion?

C6H12 + 9O2 --------> 6H20 + 6CO2

(edited 8 years ago)

Reply 334

username986184

Original post by Jassy16

What volume of oxygen, in cm³, would be required for 0.1 moles of cyclohexane to undergo complete combustion?

C6H12 + 9O2 --------> 6H20 + 6CO2

What have you done to approach this question? I did this in my head (no writing down anything) and although I do not expect you to be able to do that, I would have thought that at this point in A level you would be able to do this question.