OCR B (Salters) F336: Individual investigation 2012/13

Yes, did you do it also?

I dont suppose you could send me those examples too? i am very stuck at the moment on the bromine investigation!

anyone got any good pointers for Cu ion analysis? im a little nonplussed after the reticence of my teacher to hand out much help, and i need to get a good chunk of it done by friday week...

I'm doing peroxodisulfate and iodide, and the horrible part is that the rate constants (k) for both concentration are so different, one is 12.5 and one is 21.3 and I have no idea how to find the actual rate constant to put in my rate equation. I don't think I can add those two together and divide by 2 cuz they are far too different....anyone got any ideas?

ahh yup, got 43/45 :d

i can send you mines, and also two examples, if that will help? Send us your email on pm

hi did you do the propanone and iodine reaction investigation as your coursework?

Hmm the rate constant should be the same regardless of your individual reactants. How did you work out your rate constant?

The way I did it was when I was adjusting temperature, not individual concentrations of a reactant. So for example, in 20^oC my overall reaction time was, on a average, 25.0 seconds. Then to work out the rate of reaction, I simply did 1 divided by the time. This is a simple method to work out the rate of reaction, there are other ways.

Then all you have to do is plug into your rate equation, which is typically:
rate= k x [Reactant concentration 1]^m x [Reactant concentration 2]ⁿ
You should know your original concentration of your reactants, so it should be simple to rearrange the formula to work out k.

Remember, do not vary the concentration when working out your rate constant; that will make your answers wrong.

Good luck

That's what I did. For my investigation, I had to find the reaction rate under different concentrations of potassium iodide potassium (concentration of peroxodisulfate is kept the same) and then different concentration of potassium peroxodisulfate (conc of potassium is kept the same). But the average rate constant for potassium iodide is 12.5 and for the other one is 21.3 like I said above. At first I thought the ate constant for both concentration would be about the same but they not. The order with respect to both concentration is 2.

Yes, but the only way that you can work out the rate of reaction in this case, is by studying the effect of temperature on the rate. Using a water bath, or something similar, adjust the temperatures from 20 degrees upwards; and by using ice cubes, 20 degrees below.

Then you will have the average time taken, and you do 1/t to work out the rate of reaction. Then it is a simple matter of rearranging the rate equation to get k on its own; and thus you can work it out.

Rate constant is the same, regardless of the concentrations of any of the reactants. Remember you are working out a constant, you can't change anything else.

So if you work out that during 20 degrees the rate of reaction was say 0.004 mol dm-3 s-1; and that as you say the order of both reactants is two, you work it out like this:

k= 0.004
[Concentration of reactant 1]²[Concentration of reactant 2]²

Ask your teacher if you're unsure on how to tackle temperature and kinetics in the lab

My friend did it with peroxodisulfate rather than hydrogen peroxide but I think it's the same thing (ioding clock method, right?). She's going to see if she can find a copy for you but will make no promises Have you tried having a look online? I'm still happy to send you mine for a basic outline, although I think the general layout is pretty flexible. Have you got any information from your school? I remember we got a pack written by OCR which detailed the areas that needed to be covered, labelled from A-H I think.

I know that the rate constant should always be the same but for some reason when I varied the concentration of potassium iodide and kept the conc of potassium peroxodisulfate the same, the rate constant is different to the rate constant when I varied the concentrations of potassium peroxodisulfate and kept the concetration of potassium iodide the same. I'm sorry if I confused u and I should have told u earlier that I've already done the experiments with different temperatures and got the rate constant for it without any trouble, it's just that I have to work out the rate constant to put in rate equation when I've found out the order with respect to the reactants.

Hahahaha I feel so sorry for you

Just kidding! The coursework is tough but the hard work can pay off I got 44/45 for mine and it really helped to give me confidence going into the exam, knowing I should get an A. I did the breakdown of vitamin C one (can't remember the exact title, I've tried to block it out!) and could send you my copy if you want? I think my friend did hydrogen peroxide so I could also ask her?

This coursework was the single most painful event in my entire life. No exam/coursework/crisis/panic attack comes close.

I did the Bromine clock reaction if anyone wants a few pointers.

Hahahaha I feel so sorry for you

Just kidding! The coursework is tough but the hard work can pay off I got 44/45 for mine and it really helped to give me confidence going into the exam, knowing I should get an A. I did the breakdown of vitamin C one (can't remember the exact title, I've tried to block it out!) and could send you my copy if you want? I think my friend did hydrogen peroxide so I could also ask her?