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Another question

what changes to the concentration of the sodium methanoate and methanoic acid would you need to make to decrease the pH of the buffer by one unit?

If you want to increase the pH by 1 unit, then the concentration of HCOOH would stay the same, but the concentration of HCOO^- would need to increase by a factor of ten (from 0.1 to 1). To decrease the pH by one, then the concentration of HCOO^- would need to decrease by a factor of 10 (from 0.1 to 0.001). I'm pretty sure that this works, you might want to try a few examples with it first though because I've only just tried using it on the question that we were just talking about...

Reply 2201

otrivine

Original post by MedMed12

this is all to do with feasbility :smile:

it should be a difference of atleast 0.4v between the two e values.
in addition the reaction is feasible when the E value is positive.

No thats what I was thinking but was wrong!! I am asking someone to explain to me!

cause in the Jan 2011 paper, the electrode potential was less than 0.4V and reaction still happened

Reply 2202

MedMed12

Original post by otrivine

No thats what I was thinking but was wrong!! I am asking someone to explain to me!

cause in the Jan 2011 paper, the electrode potential was less than 0.4V and reaction still happened

ohhh its always a risky one to put down..I think I put standard conditions not used and a high activation energy, but 0.4V is defo an option- maybe it just wasn't on the MS.
I do know if someone puts an answer down and its not the MS and it could be credible, they send it for a second opinion.

Reply 2203

Nuna

Original post by Brad0440

Do you mean the G=ΔΗ-TΔS? If so, you can't put an equation like that into a triangle. But to rearrange it, you simply move each term over to the other side. So if you wanted it equal to ΔH, then move the -TΔS over to make it G+TΔS=ΔH. All you have to remember is to change the sign when moving them. For example, when I move the -TΔS over, the - became a +.

how do you do it for working out T. I know T= AH/AS but I don't understand how you get that, because when you moved -TAS you changed the minus sign to a plus sign, but with moving T alone, it has a minus sign in front of it and a x sign after it...? sorry I'm just a bit confused :colondollar:

Reply 2204

ankyloser

I'm having a bit of a blonde moment - does the gradient in a rate/concentration graph give you the order? Or is it just the appearance of the graph that shows you what order it is?

Reply 2205

Myocardium

Could someone please explain question 7 on the jan 2012 paper? It doesn't seem to follow the normal method of findinc kc in a closed container :s-smilie:

Reply 2206

fayled

Original post by sidmanny

I'm having a bit of a blonde moment - does the gradient in a rate/concentration graph give you the order? Or is it just the appearance of the graph that shows you what order it is?

Appearance of the graph. The gradient can vary so it won't give you the order no.

Reply 2207

Obtas

Can anyone help me with this please??!

20130611_150507.jpg504.2KB

Reply 2208

Sarangtaec

Original post by eggfriedrice

Tbh, at our level the only square planar we'll come across is cisplatin. It's hard to predict whether something with four coordinate bonds will be tetrehedral or square planar. So it'll be safe to assume unless it's cisplatin, the complex will be tetrahedral.

With lone pairs, I'm not exactly sure what you mean. NiCl4 is made by the chlorine ligands donating their lone pair to Ni. Same with the ligands on cisplatin.

I doubt we'll be asked why a shape is tetrahedral or square planar, so for now the only reasoning we needs is "because it just is", which is a poor explanation but for our level it's sufficient.

Side note; do you happen to be a kpop fan? :B

Oh my god yes HAHAH I'm guessing cause the 'sarang' and the 'taec' you guessed? Yeah I like EXO/B2ST/2PM you?
Thanks for the info btw, I was just reading this page and got really confused so thought I'd clear it up, but yeah I don't think they'd ask us either ^-^

Reply 2209

fayled

Original post by Satta101

Can anyone help me with this please??!

If I lived my life at 90 anticlockwise to my current orientation, then I could.

Reply 2210

Obtas

Original post by fayled

If I lived my life at 90 anticlockwise to my current orientation, then I could.

lol sorry, I uploaded it from my phone

Reply 2211

MedMed12

Original post by sidmanny

I'm having a bit of a blonde moment - does the gradient in a rate/concentration graph give you the order? Or is it just the appearance of the graph that shows you what order it is?

for rate -if its straight line 'lying down' its O
straight line diagonally- then 1st
curve upwards 2nd ofer

Reply 2212

Brad0440

Original post by Nuna

Let's just use a general equation for the moment: A+B=C

If you wanted to make it equal to A, then you need to move the B over to the other side. When you move a term from one side to another, the sign changes, so this equation would become: A=B-C
Likewise, if you wanted it to equal B, then you'd move the A over to get: B=C-A

Now, if you had another equation AB+C=D and you wanted it to equal C, then you'd move the AB over in the same way to get: C=D-AB (the AB HAS to be moved over together).
If you wanted it to be equal to B, first you would move the C over to leave AB by itself: AB=D-C. Then, to get rid of the A, you need to divide by A, because (AB)/A = B (like (4*5)/5 = 4). Whatever you do to one side of the equation, you have to do to the other as well, so the equation becomes: B=(D-C)/A

Going back to G=ΔH-ΤΔS, to make it equal to T, you'd move the ΔH over to get G-ΔH=-TΔS. Then, you'd need to divide BOTH sides by (-ΔS) to get (G-ΔH)/-ΔS=T.

I hope this helped, if not just ask and I'll try to explain it again. :smile:

Reply 2213

Brad0440

Original post by Myocardium

Could someone please explain question 7 on the jan 2012 paper? It doesn't seem to follow the normal method of findinc kc in a closed container :s-smilie:

Part a? The one with dinitrogen tetroxide in it and finding Kc?

Reply 2214

Poffertje

Original post by Pride

I'm not sure I understand your question. To clarify, cis is where the alike ligands are in the same plane (eg. 2Cl- coming towards you, 2NH3 away from you). Trans is where the alike ligands are in different planes (1NH3 and 1 Cl- going towards and away).

Ah sorry, my phrasing is bad. I understand how cis/trans works, what I mean was does it matter which plane you have your ligands on but you've already answered it now, I've been putting my ligands in different planes but on same or different sides, if you understand that.
Its alright now anyway, thanks!

Reply 2215

nickiminajs

Hey

Do we have to learn colour changes for all indicators?

Thanks :smile:

Reply 2216

MedMed12

hows the past papers going guys? :smile:

Reply 2217

MedMed12

Original post by nickiminajs

Hey

Do we have to learn colour chanes for all indicators?

Thanks :smile:

if you're talking about methyl orange and phenaphetheline (or however its spelt) isnt it just orange and a purple-ish colour

Reply 2218

Wheeeto

Original post by Myocardium

Could someone please explain question 7 on the jan 2012 paper? It doesn't seem to follow the normal method of findinc kc in a closed container :s-smilie:

Basically when you take away the 3.2 from the 4 you are left with 0.8 of the N2O4, but this is essentially 2N2O4 because the 3.2 is from 2NO2, therefore the 0.8 needs to be halved to 0.4 = equilibrium moles. As there is 2dm3 of pressure both quantities need to be halved resulting in 3.2/2, and 0.4/2 so overall it is 0.2/1.6(squared). Hope that helps :smile:

Reply 2219

nickiminajs

Original post by MedMed12

if you're talking about methyl orange and phenaphetheline (or however its spelt) isnt it just orange and a purple-ish colour