Inorganic Chemistry (AQA) - A level

How exactly do u derive them? Thank you!

The best way to explain that is to give a worked example.

Suppose you are asked to write an equation for, say the reaction of phosphorus (V) oxide (P4O10) with water.

Because phosphorus (V) oxide is an acidic oxide that forms phosphoric acid (H3PO4) upon the reaction with water, you can set up the unbalanced equation:

P4O10 + H2O —> H3PO4

Now all you have to do is balance it. Since there are 4 phosphorus atoms on the LHS, there must be 4 on the RHS, so scaling up:

P4O10 + H2O —> 4H3PO4

Now counting the numbers of each element on either side:

LHS: 4 x P, 11 x O and 2 x H
RHS: 4 x P, 16 x O and 12 x H

So there are 5 too few oxygens and 10 too few hydrogens on the LHS. Because you can’t change the formulae of any species, the only way of increasing both amounts accordingly without increasing the number of phosphorus atoms is to add another 5 water molecules to the LHS. This leaves us with:

P4O10 + 6H2O —> 4H3PO4

Thank you for taking the time ti do this! How exactly did u know phosphoric acid forms? Also I think my problem is I never know what product is formed hence I can’t balance the equation as well as any other side products I wouldn’t know if there’s like co2 or h2o or h2 produced for example.

With the period 3 reactions particularly, you just have to know what the products are. The physics and maths tutor notes in my first post on this thread should help with that.

There are some general reactions that it may help if you just memorise, so that you can set up the unbalanced equation and balance it from there:

Complete combustion:

Organic compound + Oxygen —> CO2 + H2O

Incomplete combustion:

Organic compound + Oxygen —> CO + C + H2O

Metal and oxygen:

Metal + O2 —> Metal oxide

Metal and water:

Metal + H2O —> Metal hydroxide + hydrogen

Metal oxide and water:

Metal oxide + H2O —> Metal hydroxide

Metal and acid:

Metal + acid —> H2 + salt

Metal hydroxide and acid:

Metal hydroxide + acid —> H2O + salt

Metal carbonate and acid:

Metal carbonate + acid —> H2O + CO2 + salt

Good luck everyone for exams

Thank you so much for this!! I have a quick question, I looked back to past papers and I find that most questions are A2 topics with a little bit of AS. Is this always the case for Chem papers? Cos then I would know what to focus on.

One last thing, do you know all of the equations worth remembering/memorising for Physical Chemistry i.e the standard hydrogen-electrode potential. And thank you so much for all the help and advices!!

Hi , do we need to know the colours for transition metals like when it changes . My teacher mentioned that we do not but in exam questions I keep on seeing questions in which they ask for the colour change. does anyone have a list of the colours or uno where I can get it from

Usually you are given the redox half equations, along with their electrode potentials in the exam questions.

I’d probably memorise or learn how to derive the following equations:

2S2O3^2- + I2 —> S4O6^2- + 2I^- (iodine-thiosulphate titrations)

Cr2O7^2- + 14H^+ + 6e^- —> 2Cr^3+ + 7H2O (organic chemistry and redox titrations)

MnO4^- + 8H^+ + 5e^- —> Mn^2+ + 4H2O (redox titrations)

Thanks again for this, do you also mind sharing what equations worth keeping in mind/remembering for organic chemistry. I did a paper few days ago and I literally forgot about the chlorination in ozone. If you know any others - please can you list them down. Thanks a lot!