ocr a f325 revision thread

ok thank you! also can you do some revision type q's with me sometime? would really help

I think you have to know the colour changes for when aqueous ammonia is added to Cu(OH)2, what happens when you add NaOH(aq) to a solution of Cu2+ and what happens when you add conc HCl to Co(H2O)6 and Cu(H2O)6

When NH3(aq) is added to Cu(OH)2, the NH3 dissolves the pale blue precipitate of Cu(OH)2, and from a deep blue solution.

When NaOH(aq) is added to Cu(H2O)6, there is a colour change from blue to a paler blue colour - a pale blue precipitate is formed.

When adding conc HCl to Cu(H2O)6, there is a colour change from blue to yellow (it does go green first before it goes yellow).

Finally, when adding conc HCl to Co(H2O)6, there is a colour change from pink to blue.

Chromium may be a useful one to know: when it is in its +3 oxidation state it is green, and it is orange in its +7 oxidation state.

Manganese may also be handy, as it comes up in redox titrations: when it's in its +7 oxidation state it is dark purple, and it is pale pink in its +2 oxidation state.

Iron is pale green in its +2 oxidation state, and yellow in its +3 oxidation state.

There are a few other colours you may need to know - they're in the Heinemann OCR textbook. Do you use that textbook?

Either way, I hope the above information helps!

ok thank you! also can you do some revision type q's with me sometime? would really help

because if you vary the concentration of the acid and the metal, the rate means its 0 order and so rate of reaction has no effect on increasing or making the acid more concentrated.
Also, this means that the particles do not have enough kinetic kinergy in order to collide and hence, cannot exceed activation energy and so reaction does not take place.Also, reaction may be slow

Yep I do, I swear I haven't seen it in there, what page are you referring to?

I'm afraid that's not quite right, but that's a good try, well done

I'm guessing you've both heard of the oxonium ion, H3O+, and how it is involved in causing acidity? Basically, in a dilute acid, you have lots of H2O, and little H+. Due to this, a small amount of H3O+ can be formed, so due to this the rate of reaction appears to be slow. This is a similar story with very concentrated acids - there is loads of H+, but as it's so concentrated there's not much H2O. Hence, little H3O+ can be formed, causing little acidity and a slow rate of reaction.

I hope that makes sense

I'm afraid that's not quite right, but that's a good try, well done

I'm guessing you've both heard of the oxonium ion, H3O+, and how it is involved in causing acidity? Basically, in a dilute acid, you have lots of H2O, and little H+. Due to this, a small amount of H3O+ can be formed, so due to this the rate of reaction appears to be slow. This is a similar story with very concentrated acids - there is loads of H+, but as it's so concentrated there's not much H2O. Hence, little H3O+ can be formed, causing little acidity and a slow rate of reaction.

I hope that makes sense

I'm afraid that's not quite right, but that's a good try, well done

I'm guessing you've both heard of the oxonium ion, H3O+, and how it is involved in causing acidity? Basically, in a dilute acid, you have lots of H2O, and little H+. Due to this, a small amount of H3O+ can be formed, so due to this the rate of reaction appears to be slow. This is a similar story with very concentrated acids - there is loads of H+, but as it's so concentrated there's not much H2O. Hence, little H3O+ can be formed, causing little acidity and a slow rate of reaction.

I hope that makes sense

Very clever question, how did you make this! I thought it had to be with rates ?

However, even though I agree with your answer, I do think its also involved because it has low activation energy and reaction cannot take place.

yes! that makes sense! thank you I'm really worried about this exam! but more so for f324 which im retaking from jan as got a B really need to do well need AAA to meet my offer!

Thank you very much, I know you wanted a hard question, so I tried my best to think of one! I think it's to do with that too - the less H3O+ you have, the less likely it'll collide with other molecules and react with them, so the rate of reaction will be low!



I don't disagree with you, I think that's a perfectly valid point! Maybe it could be a combination of both rates and the H3O+ ion?

I'm glad it makes sense
Me too, it is worrying! But we will all get though it! You've probably heard this so many times before, but just try your best! It sounds like you're putting in the work, so you'll get there I'm sure
On the bright side, as you've taken F324 before, you have an idea of what to expect and you can own that exam this time
Ah that's cool, what course have you applied for? I hope you achieve the grades you're hoping for, it sounds to me like you deserve it

So with my answer what credit would I get?

thank you! i'm so worried! ive applied for Medicine! do you take aqa biology? if so can you give me some tips on how to tackle the HSW q's i really struggle with those

Wow nice one Which medical school are you hoping to go to? An offer from a medical school is a great achievement, congratulations
I'm afraid I don't, I do OCR Biology But feel free to try me

Hmm..obviously I made the question up, so I'm not absolutely sure. However one thing I would say is that you mentioned how it could be to do with the rate of reaction - a valid point, however I'm sure rate of reaction would come into things even if the acid were dilute or more concentrated. Personally, I think it's dictated by the H3O+ ion, because if there is no H3O+ ion then there will be no reaction. Although, with regards to you point on the rate of reaction...you could relate it to the H3O+ ion by saying how the rate is less because there's less H3O+ present, so it's less likely to collide with other molecules (although the same could be said of very dilute acids).

OK


state the colour of Mn2+ and Fe(OH)3 (S)

I hope I wasn't being unfair, please feel free to tell me if I am

Mn2+ is light pink in colour, and Fe(OH)3 is a precipitate that is orange-brown in colour.

In an iodine-thiosulfate titration, how can you mark the end point?

.. how to attach files into thread, anyone?

I hope I wasn't being unfair, please feel free to tell me if I am

Mn2+ is light pink in colour, and Fe(OH)3 is a precipitate that is orange-brown in colour.

In an iodine-thiosulfate titration, how can you mark the end point?