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OCR B (Salters) F336: Individual Investigation 2013/14

Reply 80

nick d terrier

10

Hello does anyone have a plan for the write up ? like a breakdown of headings and sub-headings and what to include

Reply 81

SherlockHolmes

13

Original post by yl95

Ah, OCR B for two subjects! Unlucky. I don't do Physics so I'm safe. I do have to write synoptic essays for Biology, though. ;_:

Yeah, I got some dodgy results and so did a few people so they had to fudge their results. :colondollar:

Congrats on the Impy offer. :smile:

Might be seeing you there, seeing how lectures for both Maths + CompSci are in the Huxley building. I need As in both Biol and Chem and an A* in FM for my offer. I applied for the joint course so I'll be having the best of both worlds...if I get the grades(!).
Did they ask for a 2 or 1 and did they specify which ones? It's harsh of them to put people through the MAT AND STEP. Imperial have been really mean this year; 3A* 1A offers for ChemEng, STEP offers for JMC, UMS requests for Physics...

I think everyone needs to forge data to be honest. We are all amateur chemists at best so getting good and reliable data never seemed likely. In my class, catalysts have been slowing reactions down...

Well done on your offer :smile:

I hope to see you at Imperial too. My offer is A* FM, an A in Physics and 2 in STEP II or III. I don't even need chemistry! I will settle for a B in chemistry as it isn't too important for me.

Reply 82

username638250

7

Original post by SherlockHolmes

I think everyone needs to forge data to be honest. We are all amateur chemists at best so getting good and reliable data never seemed likely. In my class, catalysts have been slowing reactions down...

Well done on your offer :smile:

I hope to see you at Imperial too. My offer is A* FM, an A in Physics and 2 in STEP II or III. I don't even need chemistry! I will settle for a B in chemistry as it isn't too important for me.

Haha, that's true. I'm much more of a theoretical chemist, to be honest. Coursework just isn't my thing.

Thanks! I guess they couldn't ask for more seeing how they asked for STEP as well. Have you started STEP prep?

I really want an A at least but I honestly have no idea what I'm going to get in the coursework. I spent AGES on this.

Reply 83

SherlockHolmes

13

Original post by yl95

Haha, that's true. I'm much more of a theoretical chemist, to be honest. Coursework just isn't my thing.

Thanks! I guess they couldn't ask for more seeing how they asked for STEP as well. Have you started STEP prep?

I really want an A at least but I honestly have no idea what I'm going to get in the coursework. I spent AGES on this.

I get good grades for coursework but the problem is I need a lot of time if I am to complete it well. I will spending all my frees (and lunch break) this week trying to get this done.

I started STEP prep after the MAT. I was only going to take STEP I and not really aim for a particular grade as I wasn't expecting STEP to be a condition I had to meet for one of my offers. I haven't really done many questions but should be able to practise a lot more once this is coursework is finished.

Will you be taking STEP?

Reply 84

username638250

7

Original post by SherlockHolmes

I get good grades for coursework but the problem is I need a lot of time if I am to complete it well. I will spending all my frees (and lunch break) this week trying to get this done.

I started STEP prep after the MAT. I was only going to take STEP I and not really aim for a particular grade as I wasn't expecting STEP to be a condition I had to meet for one of my offers. I haven't really done many questions but should be able to practise a lot more once this is coursework is finished.

Will you be taking STEP?

It depends on the coursework for me but generally, I don't put that much effort into stuff that counts throughout the year. :P Obviously, now that things matter, that's changed. I've done the same as you; I even bunked off one of my compulsory General Studies sessions to do my coursework... -shock horror-

No, I won't be. I'd rather get really good grades at the moment than risk not meeting my 4 grade offer. Having said that, STEP questions are really interesting and I'll probably be doing them after my exams for fun.

There's also the Imperial Offer Holders Page on Facebook; it's only got 56 members or so, which is little in comparison to the Oxbridge ones. ;P

Reply 85

The_Blade

6

Original post by StephenNaulls

I am! Any tips?

What experiments have you done?

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Reply 86

MiaSmithy

Hi,

Sorry to post again but could really do with some help!

I did my experiment of quenching and titrating potassium iodide and potassium peroxodisulfate with sodium thiosulfate so the solution went from colourful to colourless

From the volume of sodium thiosulphate needed to titrate each small sample taken from the main mixture at different times i worked out the concentration of iodide made in the solution at the time (via the reaction S2O8 ^2- + 2I^- --> 2S204^2- +I2)

So i plotted a graph of the concentration of iodine in each sample taken at different times, against the time they were taken and got this shape -

concen of iodine.png

I geuss this makes sense as the longer you leave the solution, the more iodide made so the higher the concentration.

But how can I use this data to find the order of reaction with respect to iodine?

PLeaseeeeee help :smile:

Reply 87

Phteven

15

Original post by The_Blade

What experiments have you done?

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Bromate-Bromide reaction...

Reply 88

SyedaK

11

Original post by MiaSmithy

Ah thank you, i'm been researching titration with quenching and I have a proposed method -

Put an excess of potassium iodide (why excess?) with potassium perxodisulfate in a conical flask, and the reaction

S2O8^2- + 2I^- -> 2S04^2- + I2

occurs, as the peroxodiulfate acts as a strong oxidising agent.

Take small amounts of this mixture at known time intervals, e.g every five minutes, place in a conical flask with ice cold water, or something that will stop the reaction? (any help with that bit would be great) and maybe add the starch at this point? ( help here would be great too! ) Note that blue black colour appears when iodine reacts with the starch, not iodide ions wich are colourless

Then titrate the sample with sodium thiosulfate where this reaction will occur -

I2 + 2S2O3^2- -> S4O6^2- +2I^-

as the thiosulfate ions react with the iodidne, reducing it back to iodide, the colour of the solution will change from blue-black to colourless. Once this occurs, the volume of thiosulfate needed will indicate number of moles of iodine present (half of this) and the number of moles of peroxdisulfate reacted ( as ratio of persulfate to iodine is 1:1).
From this i think you can work out rate equation and constant but not exacty sure how? (help here too please)

But you can find the order of iodine, by plotting the concentration at different time intervals (worked out from the eqautions and the info above i think agsint the time

i'm not 100% sure about the method as you can probably tell! i also wonder that as your putting an excess of potassium iodide in, the change in it is small so it will no longer appear in the rate equation? as explaiend by http://www.youtube.com/watch?v=x5Jf_RJhZHY when normally it does?

Also how does this method compared to the clock method? can you still change the concentration of the different reactatants, use catalysts etc with this method?

any help would be amazing, sorry about all the questions!

Thank you :smile:

Ah thank you, i'm been researching titration with quenching and I have a proposed method -

Put an excess of potassium iodide (why excess? I don't think it matters how much you put - I'm not too sure about this ) with potassium perxodisulfate in a conical flask, and the reaction

S2O8^2- + 2I^- -> 2S04^2- + I2

occurs, as the peroxodiulfate acts as a strong oxidising agent.

Take small amounts of this mixture at known time intervals, e.g every five minutes, place in a conical flask with ice cold water, or something that will stop the reaction? (any help with that bit would be great - For my one, I'm using sodium thiosulfate because it stops the reaction but I think for your one sodium hydrogen carbonate is a good one) and maybe add the starch at this point? ( help here would be great too! Yup you should add starch here ) Note that blue black colour appears when iodine reacts with the starch, not iodide ions wich are colourless

Then titrate the sample with sodium thiosulfate where this reaction will occur -

I2 + 2S2O3^2- -> S4O6^2- +2I^-

as the thiosulfate ions react with the iodidne, reducing it back to iodide, the colour of the solution will change from blue-black to colourless. Once this occurs, the volume of thiosulfate needed will indicate number of moles of iodine present (half of this) and the number of moles of peroxdisulfate reacted ( as ratio of persulfate to iodine is 1:1).
From this i think you can work out rate equation and constant but not exacty sure how? (help here too please in order to work out the rate equation, you have to first find the overall order of reaction by plotting a graph with each concentration against time. Then you draw tangents and work out the initial rate. From there, you plot a graph with rate against concentration and determining the order of reaction with respect to the reactant from the graph. This should help http://www.chemguide.co.uk/physical/...erimental.html )

But you can find the order of iodine, by plotting the concentration at different time intervals (worked out from the eqautions and the info above i think agsint the time

i'm not 100% sure about the method as you can probably tell! i also wonder that as your putting an excess of potassium iodide in, the change in it is small so it will no longer appear in the rate equation? as explaiend by http://www.youtube.com/watch?v=x5Jf_RJhZHY when normally it does? (I'm not too sure about this)

Also how does this method compared to the clock method? can you still change the concentration of the different reactatants, use catalysts etc with this method? - With the clock method, it more about looking at the colour change and stopping the time while with the titration, it's reaching the end point at regular time intervals. That's the difference and you can definitely change the concentrations. For example, if you're changing the concentration of potassium iodide, maybe for the first concentration you add 0.1moldm3 of potasssium iodide with 1moldm3 of catalyst and moldm3 of peroxidase sulfate - you add the quenching substance before adding the potassium iodide and then start the timer immediately and titrate at set intervals. Just remember to change one reactants concentration while controlling the others.
any help would be amazing, sorry about all the questions! Sorry for the late reply and apologies if this was no help. I'm also struggling with mine.

Thank you

Reply 89

The_Blade

6

Original post by StephenNaulls

Bromate-Bromide reaction...

Lol.

Did alter concentration, temp etc

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Reply 90

Mohid Khan

14

any one here doing the copper one? or the electrochemical cell one?

Reply 91

Annaaanaaaa

Hi,
is anyone doing the bromide, bromate and the hydrogen ions one, if so has anyone got any examples really really stuck

Reply 92

kaitlyn_123

Hello everyone!

Is there anyone else doing an investigation on the percentage purity of aspirin in different storage conditions (looking at rate of hydrolysis)??
A difficult one, still wondering why I picked it

Reply 93

SherlockHolmes

13

Does anyone know if references are only for the background theory or is it meant to include methods, risk assessment etc as well?

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Reply 94

TwlilightLoz

1

Can someone help me out, im stressing out over the experiment where we find the rate of reaction between magnesium and hydrochloric acid by measuring the hydrogen gas produced via a gas syringe. I think its experiment number 5 in the experiment sheet we were given.

Firstly: I don't understand how much volume of acid i'll be given or how much I should use etc.
Secondly: How do I dilute 2M of hydrochloric so I end up with 1.5M, 1M and 0.5M of HCl and what volume should I start of with? The sheet says to put 20cm3 of 2M HCl in the the buchner flask with magnesium. Does this mean that I should put 20cm3 of 1.5M, 1M and 0.5M of HCl into the flask with magnesium to find the rate of reaction with the respective HCl concentrations? Again, how would I dilute the HCl to get the required concentrations?
Thirdly: Im going to measure the hydrogen gas produced in 10 seconds intervals. From this, how do I find the rate of reaction between magnesium and HCl? And how would I draw a graph of it?

Anyone whose done this experiment before and would like to help me out or point to me in the right direction and PM me

Thanks for the help :smile:

Reply 95

SherlockHolmes

13

Original post by TwlilightLoz

...

If you have 2M HCl and you want 20cm^3 of 1M HCl, use 10cm^3 of 2M HCl and 10cm^3 of distilled water. Similarly, for the other concentrations use the formula below and top up to 20cm^3 with distilled water.

concentration of 20cm^3 solution = (concentration of HCl x volume of HCl)/total volume

Reply 96

twimple

Hi FP. im doing electrochemical cells.
If anyone else has done this what results did you get? I got some really messed up results when changing concentration of ZnSO4 against 1M CuSO4.

(also pretty sure this isn't cheating as you dont get marked on what results you got, but how you evaluate them.)

Reply 97

Mohid Khan

14

Can you use both as solutions of copper sulphate or does one have to be zinc

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Reply 98

Tedstain

Original post by Mohid Khan

Can you use both as solutions of copper sulphate or does one have to be zinc

you can do anything you want.
Personally I just kept zinc sulphate at 1M and varied the concs of copper, and then kept copper sulphate at 1M and varied concs of zinc.
Have you done the practical?