This discussion is now closed.

Check out other Related discussions

OCR A2 Practical...How Was it???

Finished mine about 10 mins ago...... didnt really like it, the actual experiment was easy, ive done one in class before like it. its just the explaining stuff which i found was hard!!
much prefered the physics on monday

What did everyone say for the last 3 bits when it said why a pippette was innacurate and the measuring to 0.01s? i said that when you add the KI from the pippete it takes ages so the reaction would of allready started by the time you have added it all. for the timing one, i said human reactions are only like 0.2 second so 0.01 seconds wouldn't be useful. couldnt think of n e thing else!

..:: Sim ::..

Reply 1

fairysparkle

i hated the evaluation part! I just sat there staring at the paper hoping for inspiration but it never came! I struggled to find three reasons for the measuring cylinder as well, and couldnt work out the order! Oh well lol, at least its over now.

rachel

Reply 2

Liana89

Hey finished mine like an hour ago and thought most of i was ok, but the evaluation bit was weird, I put for the KI thingy that it was in excess so i didnt really matter being a bit more accurate, and for the one of the 0.01s that it wudnt change the shape of the graph being a bit more accurate, cos your trying to find the order,

liana xx

Reply 3

milesalexanderappleyard

3

Easiest one I have ever done. :smile:

Reply 4

aisha06

oh crap. Have got a few of those wrong for sure. I couldn't do the evaluation to save my life.To be honest, i think its really unfair that some people knew a LOT more about what the practical was going to entail than others. Ah well at least its over!

Reply 5

Wangers

16

Yes agree with those Vb, looks fine :biggrin:

.

Reply 6

Schmooface

Well it looks like i screwed up royally!! the evaluation was so hard :frown:

Reply 7

Oh Dear...

12

On the Evaluation, did the second question ask 'How reliable were your results?' or 'How reliable was the apparatus'?

Because im worried i wrote the wrong answer...

Reply 8

londonkid89

Oh Dear...

On the Evaluation, did the second question ask 'How reliable were your results?' or 'How reliable was the apparatus'?

Definitely results..otherwise I might have got it wrong :frown:

Reply 9

Oh Dear...

12

Thanks. Thats what I thought too. But then somebody told me it was about the pipette accuracy...

Made me worry...

Reply 10

londonkid89

Oh Dear...

Made me worry...

Everyone in our college was talking about it (who wasn't lol) and because some of us had different answers from others it worried me a little, so I just stopped talking about it! lol..apart from here though, hehe

Reply 11

Rainbow24

8

Why was the chemical being investigated hydrogen peroxide? :confused:

Reply 12

7589200

18

yeah but for that result use V = 26 not V = 25.

Reply 13

7589200

18

well i dunno, like i said, there are usually loads of things to say for the evaluation sections
its just, if u added 26 in, u can plot that point at 26 and use the time u got for it, and itd be just the same as plotting the point at 25 (ie. one more accurate point)

Reply 14

eyanian

I found it pretty hard compared with other practicals and made a load of mistakes on the evaulation. i read your post vb , and by the looks of it u did v well. However as for the question 'how reliable are your results', u wrote ' very reliable', i totally diagree. i wrote the reverse saying the experiment was only done once, cumalative errors increased from transfer of lots of chemicals and though the results produced a clear line on the graph it may have been by chance. I thought the only way to get reliable results was to do many repeats and get concordent results? Then again, i may be wrong bt it seemed logial. As for the last question about the results i also put disregard it as an anomalus result and repeat experiment. Nice experiment , v nasty evaluation.

Reply 15

Viagra

vb07

well i dunno, like i said, there are usually loads of things to say for the evaluation sections
its just, if u added 26 in, u can plot that point at 26 and use the time u got for it, and itd be just the same as plotting the point at 25 (ie. one more accurate point)

I think vb 07 's answer is close to MS perfection!!!! I bet you will get full UMS for this. Well, you do have a Cambridge Medicine offer...

I have to say that I am not entirely sure why you would write RDS for proving the reaction is first order if you don't know what the rate equation is/
And for the last question, don't you just exclude the invalid data, then repeat or plot a graph and extrapolate to estimate? Your answer seems unusual as I don't think the examiner would expect us to refer the log equations?

PS Please excuse my stupidity if any of my comments are wrong as I am a Cambridge Natsci reject afterall!

Reply 16

7589200

18

nah its nothing to do with logs really
its like this
If you were plotting say the amount of volume (V) against time (T) for example and u were adding 1 cm3 each time,

V = 0 T = 0
V = 1 T = 1
V = 2 T = 2
etc..
at the end you find out that ur last volume (which took 6 seconds) isnt 5 cm3, its 6, because you put 1 cm3 too much in,
instead of plotting ur final point as V = 5 and T = 6, you simply use V = 6 and T = 6. You'll still get a graph which works and the mistake of adding too much in wont matter at all.

So similarily, you could have used V = 26 cm3 instead of 25 cm3 on your graph and you wouldn't have ruined the trend.

As far as reliability goes, its really up to how ur results were. There are two things with reliability usually. Firstly, do the points lie close to the line and secondly, were repeat readings done for each value done. I meant very reliable with regard to the first bit really. With the RDS, what i mean is that NaThio wasnt really involved in the main reaction (it was only being used to alter the concetration of the H2O2).

OCR A2 Practical...How Was it???

Related discussions

Latest

Trending

Trending

Articles for you