Official A2 OCR Chemistry Practical Thread Watch

Talya
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#61
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#61
For the x value I got 7, i know it was meant to be 6 but I did all the calculations correctly using my values, so I should still get the marks
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shyopstv
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#62
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#62
I didn't even get as far as working out x because I ran out of time. I worked out the Mr of the compound to be 380 which is a bit worrying because that was the value they told you to use if you couldn't work it out which is usually quite a long way off the actual value.

I came out with two points for the evaluation one of which I am pretty sure is wrong
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w8wizz
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#63
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#63
for x i got 183, i dont know where i went wrong because i cant remember parts of the question.
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Aired
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#64
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#64
(Original post by shyopstv)
I didn't even get as far as working out x because I ran out of time. I worked out the Mr of the compound to be 380 which is a bit worrying because that was the value they told you to use if you couldn't work it out which is usually quite a long way off the actual value.

I came out with two points for the evaluation one of which I am pretty sure is wrong
I got 383 and most of the people I spoke to at college got something between 380 and 385.

Did you all find the end point in the titration hard to see?
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keyka
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#65
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#65
yes! the change was meant to be from green/grey to a purpley colour, but the purple i was getting was quite grey, so i wasn't sure if it had changed! i thought the evaluation would then be something to do with this but it wasn't at all!

time was also a huge problem. i did have to do 4 titrations (1 rough and 3 accurate) which slowed me down a bit, but some people only did 2 including the rough and were still short on time!
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Aired
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#66
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#66
Yeah, mine was like that as well. The final colour was like purple/grey
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spicypixel
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#67
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#67
Hey, it’s my first post but here it goes.

I took the OCR A2 practical test today as well in St Albans, Marlborough School. The test seemed to cover WAY too much in the time allotted, also I ended up with an X of 5.8 approximately and I rounded it to 6 because I faintly remembered it would be 6 for this experiment. Ummm I only just got onto the part where you heated the test tubes because my titration went a bit wrong, albeit ending up with 23.9cm3 in the end for my mean titre. Our teacher said he did it the previous night as he had to and it took a lot longer than the time allotted, and as such he’s writing to the exam board to explain this, might be a nice idea to persuade your chemistry teachers likewise, and should boost the marks a bit.

Overall it wasn’t too hard I think, just time consuming and at some points frustrating. I do hope I scraped enough marks to pass it… and the plan wasn’t very useful, as usual.

Overall I suppose it could have been worse.
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UT Master
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#68
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#68
1 Rough And 3 Titres? Lol It Told You To Do 1 Rough And 2 Titres Only, So Why Waste Time Doing 4?
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Aired
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#69
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#69
You had to get 2 concordant titres it said
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Talya
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#70
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#70
(Original post by Aired)
You had to get 2 concordant titres it said
No it didn't, it said 2 accurate ones.
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Aired
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#71
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#71
Oh right. I only did a rough one and then two accurate ones anyway
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sharp-spark
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#72
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#72
Yea, im pretty sure it said to do only two accurate ones as you wont have time to do lots of repeats.

I didnt find it too bad, however after discussing it with peeps im not feeling too confident on the calculation questions.
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Joy_A
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#73
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#73
My teacher got a titre value of 23.20 and i got 23.25 so i think i got full marks on that.. :P

The moles (x) of H20 was 6

What i never got right (or know how to work out) was the % error, anyone know the method??
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Aired
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#74
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#74
% error = (Level of accuracy, i.e. 0.06cm3)/(amount measured) x 100%.

What was your mass of the solid Joey?
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tozhan
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#75
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#75
i got x=8 i now know it was ment to be 6 but hey ho...

22.2cm3 was my average titre.

loved every minute of that experiment. i still havnt recovered, its been 3 days.

most people in my class either didnt finish or only just had time so i expect the grade boundaries will be raised significantly.

also, i got 3990 for the relative molecular formula and i went back through the calc 4 times, didnt find a single error!! im obviously out by a factor of 10 but then i find out 2 other people in my class also out by factor of 10. Any1 here experience that??
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tozhan
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#76
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#76
just had a thought...do you think it might have been that i took at 25cm3 aliquot from a 250cm3 standard solution and messed up the calcs??? i think i just found my factor of 10. what a biatch.
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Talya
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#77
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#77
(Original post by tozhan)
im obviously out by a factor of 10 but then i find out 2 other people in my class also out by factor of 10. Any1 here experience that??
Yeah, one guy in my class was, and he's very clever!
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shyopstv
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#78
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#78
I was also out by a factor of 10 until I realised that I didn't divide the mass of the iron by ten - the average titre is what reacted with what was in the conical flask not the volumetric flask. It was quite easy to miss because normally they put that in as another question
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Solid_L
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#79
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#79
Yeah, I was struggling with that^ Wondering why I was out by a factor of 10...but at the end of the end of the paper I got it just
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Joy_A
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#80
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#80
lol....i too missed out by a factor of ten but i realised straight away wen i got my silly RMM of 3 thousand summink... :P
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