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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016)

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Original post by tamoni4
What was the % error? My answer was something like 1.7%. And I've said that to decrease the error you have to add a bigger mass of hydrated salt so that more water would be lost which will decrease the (error / mass) fraction.


I got 1.7% also.... I did 2 x 0.005 and then divided that by 0.58g ?
Original post by SGHD26716
I used 100 as they mixed the two solutions together


Did they?? Dang it! Would i still get some marks for correct working out albeit with wrong numbers?
Original post by snickercell
For the q=mct question would the mass have been 50cm3 because that was the mass of the solution they used?? I'm confused because some used 100cm3 and others 50cm3?? Also did anyone get the equilibrium question??? Because surely low temperatures wouldn't have produced a better percentage yield since the forward reaction was exothermic so low temp would shift equilibrium forward??? Also the high pressure would shift equilibrium to the right hand side since there were fewer molecules?? I just don't get that question at all


Low temperatures push the reaction to the exothermic side. And the forward reaction/ product had less molecules than the reactants. So increase in pressure pushed the equilibrium to the product side. And then you talk about how high pressure costly blah blah.
Original post by therealbatman365
I got 1.7% also.... I did 2 x 0.005 and then divided that by 0.58g ?


Also got that but wasn't 100% sure if we had to round to 2% as 0.01 increments which is 1sf?
Original post by 87Mack
did anybody get 0.768 for conc of so3?


AHCK You needed to square root it, cos that value is (SO3) squared. I got about 0.876moldm-3.
Original post by 87Mack
i put B


Same fammmmm 👌🏾
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87Mack
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ngl that paper was pretty easy
Original post by snickercell
Did they?? Dang it! Would i still get some marks for correct working out albeit with wrong numbers?


Certainly but not sure how many with it being a new spec and all
Original post by therealbatman365
What did y'all put for q15 about the non-polar e/z isomers on MCQ?


That one messed me up and I ran out of time at the end to finish working out, I think i put A because B (or C) wasn't even E/Z.
Original post by therealbatman365
I got 1.7% also.... I did 2 x 0.005 and then divided that by 0.58g ?


Yes, exactly. Since there were 2 measurment, you had to double the error and then divide by the mass of water and multiply by 100.
(edited 7 years ago)
Stewy fails chemistry
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Original post by Barklimus
AHCK You needed to square root it, cos that value is (SO3) squared. I got about 0.876moldm-3.


nah why do you square it? there was only one mole of SO3
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Original post by therealbatman365
Same fammmmm 👌🏾


yes yes my g
Original post by RadonGhost
What did people get when it asked for the equilibrium concentration of SO3 in the question asking about yield, I got something like square root of 30 after rearranging the equation and simplified, but I'm pretty sure that's wrong?


sqrt 30 is around 5 mol per dm^3, which is really big, especially considering Kc was closer to 0 than 1 so there should be more reactants than products

Original post by therealbatman365
What did y'all put for q15 about the non-polar e/z isomers on MCQ?

I put the E isomer with the chlorines on each side of the double bonding carbons, it looked like they'd cancel out that way
Original post by Barklimus
AHCK You needed to square root it, cos that value is (SO3) squared. I got about 0.876moldm-3.


Your answer would give 0.14 Kc if I remember correctly with it being like [SO4]^3/2^2 x 1.2 = 0.16?

I think I got about 0.916 or something working it out now but can't remember if those numbers are right
(edited 7 years ago)
Original post by jn998
They said to assume the mass of the solutions was the same as water


That was so you could use C=4.18. :smile:
For the question on polarity, I am sure it is C, due to the fact that if you draw the molecule , it is symmetrical, thus poles repel.
how can ya'll remember what you got for maths questions? I forget as soon as i come out!
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Original post by Jitesh
Are you sure he didn't give the cubed root number? Your answer would give 0.14 Kc if I remember correctly with it being like [SO4]^3/2^2 x 1.2 = 0.16?


where did S04 come from i swear it was just SO3
Original post by h3rmit
sqrt 30 is around 5 mol per dm^3, which is really big, especially considering Kc was closer to 0 than 1 so there should be more reactants than products


I put the E isomer with the chlorines on each side of the double bonding carbons, it looked like they'd cancel out that way


My answer was B.

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