Edexcel chemistry 1 Watch

SK-mar
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#621
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#621
(Original post by RUGRLN)
For the risks I put that a heating mantle or something should be used since flammable..and the tube was filled up right to the top meaning no room for gas to escape?
I thought about the bung and clamp...but they were more like errors than risks that could do harm...but I'm not sure..
well considering the bung didnt fit, the gas could escape which is a risk. Plus if the test tube in the water wasnt supported it could fall causing the gas to further escape which again is a risk.
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franco1000
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#622
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#622
(Original post by frankie einstein)
January 2010 A thresholds;
Unit 1: 48/80
Unit 2: 51/80

Good luck to everyone

wooot then wt is 76/120 ums
cose i did it in january n the result sheet sed it was a C. thats y i retook it in may.:confused:
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KubanaN
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#623
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#623
What did you say for the question which was asking if some compound could be represented as ionic model or something like that. I said no because it was like 98.5% ionic. Wasn't sure about that because it was really close to 100%.
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FallenPetal
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#624
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#624
I don't get what people are saying about 'recognizing' something as being endothermic and swapping the sign round. Surely, if Hess's law is applied, the energy should cancel out on it's own.
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KubanaN
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#625
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#625
(Original post by FallenPetal)
I don't get what people are saying about 'recognizing' something as being endothermic and swapping the sign round. Surely, if Hess's law is applied, the energy should cancel out on it's own.
In Hess's Law if you done calculations correctly sign will be correct. But with the formula (m x c x delta T) divided by amount of moles used up, depending on how you calculated the temperature change it can vary the sign in your answer so for eg. temerature changed from 16.8oC to 54.5oC you could calculate it it as -37.7oC or +37.7oC. So your answer will have either positive or negative value. But for example all enthalpy changes for combustion are exothermic so the sign must be negative, so if your calculated value was positive change it to negative and if it was negative leave it as negative. If the temperature fell down reaction is endothermic, and if rise its exothermic. This is how I work out the sign.
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FallenPetal
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#626
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#626
(Original post by KubanaN)
In Hess's Law if you done calculations correctly sign will be correct. But with the formula (m x c x delta T) divided by amount of moles used up, depending on how you calculated the temperature change it can vary the sign in your answer so for eg. temerature changed from 16.8oC to 54.5oC you could calculate it it as -37.7oC or +37.7oC. So your answer will have either positive or negative value. But for example all enthalpy changes for combustion are exothermic so the sign must be negative, so if your calculated value was positive change it to negative and if it was negative leave it as negative. If the temperature fell down reaction is endothermic, and if rise its exothermic. This is how I work out the sign.
Ah. I was getting the calculations mixed up in my head. That makes sense, ty
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Craydot
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#627
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(Original post by KubanaN)
What did you say for the question which was asking if some compound could be represented as ionic model or something like that. I said no because it was like 98.5% ionic. Wasn't sure about that because it was really close to 100%.

I said yes, because the values were in good agreement (3%) which suggests the compound is almost purely ionic.
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kaven
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#628
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#628
do you think the grade boundaries will be roughly the same as the unit 1 exam in january...or higher....or lower ?
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shadow12345
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#629
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#629
Some 1 upload tge paper pla
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emilylikeeee
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#630
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#630
(Original post by CityOfMyHeart)
I put 5 peaks.

One at 79, one at 81.
And then three for the molecule combination because Bromine's diatomic (so peaks at 79+79, 79+81 and 81+81).
Me too! Though we seem to be in the minority for this one :|
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kaven
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#631
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#631
(Original post by emilylikeeee)
Me too! Though we seem to be in the minority for this one :|
what is the answer to that question !?

I put 3 ...but then quite a few people are saying 2 and 5 as well

hmmm....
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RUGRLN
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#632
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#632
(Original post by FallenPetal)
I don't get what people are saying about 'recognizing' something as being endothermic and swapping the sign round. Surely, if Hess's law is applied, the energy should cancel out on it's own.
That's what I'm thinking...I found the Hess's Law cycle to be -726kJmol on the exam.
I tried it at home now using Wikipedia's ΔH values and found -680kJmol...so I don't think +ve value should've been found
This is what I did:
ΔΗ2= ΔH of CH3OH
ΔΗ1= ΔH of 2*Water and CO2
ΔΗc = ΔΗ2 - ΔΗ1
ΔΗc = (-283.4) - (-393.5 + (2*-285.2) )
= -680kJmol
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woozeybear
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#633
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#633
(Original post by RUGRLN)
That's what I'm thinking...I found the Hess's Law cycle to be -726kJmol on the exam.
I tried it at home now using Wikipedia's ΔH values and found -680kJmol...so I don't think +ve value should've been found
This is what I did:
ΔΗ2= ΔH of CH3OH
ΔΗ1= ΔH of 2*Water and CO2
ΔΗc = ΔΗ2 - ΔΗ1
ΔΗc = (-283.4) - (-393.5 + (2*-285.2) )
= -680kJmol
It was the question where you had to work out the J from mc/\T and then find out the number of moles, and then find out kJmol-1 and you had to put a - in front because heat was given out
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RUGRLN
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#634
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#634
(Original post by woozeybear)
It was the question where you had to work out the J from mc/\T and then find out the number of moles, and then find out kJmol-1 and you had to put a - in front because heat was given out
Yea that I knew...but some ppl were saying about doing it for the Hess' Law cycle...anyways...enough of this!
Now I gotta tackle bio!
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woozeybear
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#635
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(Original post by RUGRLN)
Yea that I knew...but some ppl were saying about doing it for the Hess' Law cycle...anyways...enough of this!
Now I gotta tackle bio!
Oh ok..maybe they got the arrows the wrong way round or thought they changed the sign when they didn't? I don't know really..
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SK-mar
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#636
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#636
(Original post by KubanaN)
What did you say for the question which was asking if some compound could be represented as ionic model or something like that. I said no because it was like 98.5% ionic. Wasn't sure about that because it was really close to 100%.
I also said no because the values were different by about 35KJmol-1 or something so i said that implies that the coumpound was partially covalent. However, you could also say yes by saying that they are in such close agreement with each other so it is almost purely ionic. But it was the 'almost' that made me say no cos its not exact.......Someone earlier said that the markscheme should allow both yes and no if you then followed your answer with a suitable explanation as to why.
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laurenwsw
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#637
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#637
(Original post by johnnym15)
yh i put u needed a bigger bung and that the delivery tube was nt directly underneath the test tube so flammable gas would escape and could ignite with the flame of the bunsen
I thought that it might be something to do with the fact that water can back flow into the delivery tube. I also wondered why they used alluminium oxide as the catalyst because I thought that alluminium oxide was used in reforming ??
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SK-mar
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#638
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#638
My prediction is 58/80 for an A on this one. It was a decent paper so i believe it will have the highest boundary yet... previous years were:
jan 09 - 53
june 09 - 57
jan 10 - 48
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SK-mar
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#639
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#639
(Original post by laurenwsw)
I thought that it might be something to do with the fact that water can back flow into the delivery tube. I also wondered why they used alluminium oxide as the catalyst because I thought that alluminium oxide was used in reforming ??
aluminium oxide and silicon oxide are definitely used in cracking.
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oh lord help me
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#640
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#640
(Original post by Aerox217)
Paper was decent, but I'm absolutely disgusted with myself for losing easy marks. Feel stupid as fuuuuuuuuuuu. Think I may have just thrown away an easy paper :/
But some questions were WTF? Last question = -2 marks for me. -4 marks on other question. About -6 marks from silly 1marks lost here and there. And I'd expect about 16-18/20 on multiple choice.
Grade boundaries BETTER be low. Anyone know the Jan2010 boundaries cos I can't access the examiners reports?

OMG this this this!!

It was the easiest ****** paper and I threw away tonnes of marks because I focused my revision mainly on the hard stuff I thought would come up such as radical substitution etc etc. By doing this I totally put revision of the 'easier' chapters on the bench, and whaddya know, thats all the stuff that comes up.

I'm disgusted with myself. Resits here I effing come.
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