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Edexcel - Chemistry Unit 2 - 4 June 2013

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Original post by James A
I put flame test, but when you react Magnesium Carbonate, with a particular sulfate, won't you get magnesium sulfate, which is then soluble in aqueous and barium sulfate, which is not soluble in aqueous? :s-smilie:


Yeah, very good!

But it should not bu sulfuric acid (no acid was allowed) and both barium and magnesium should be able to displace it.

EDIT; on second thoughts I dont think it should be more reactive or anything. Its a precipitation reaction
(edited 10 years ago)
Reply 1481
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Meehar17
put the flame test for the 1 marker at the top of the page and thermal decomposition for the 2 marker at the bottom of the page
I got that too.
Its because you read the burette twice, at the start and the end.

This was posted from The Student Room's Android App on my GT-S6500
I asked my teacher about the flame tests and he says that its the correct answer.
Original post by geor
What did you guys put for the difference between the solutions?


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difference between the solutions? You mean the excess iodine that was left?
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posthumus
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20
Is POCl3 a red solid by any chance ? :colondollar: :tongue:
Reply 1486
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Original post by geor
What did you guys put for the difference between the solutions?


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Pale yellow to colourless for titration with no indicator

Colourless to red brown for br- to br2 reaction


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Original post by geor
No the one before comparing Ba and Mg carbonate


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flame test.

No flame colour with magnesium, a green flame with Barium.
What were your thoughts on acid preventing the hydrolysis of bromine?
For the titration question, one question was how to improve the reliability. I said divide the iodine solution into smaller portions, titrate several times and calculate the mean titre. And then they asked you to calculate the percentage error (I got 0.86%). Then after that the question was how to reduce the % error, I said use a less concentrated solution of sodium thiosulfate so that the volume needed to react with the iodine would be larger. Larger volume --> less % error.

Anyone else did the same? :smile:
(edited 10 years ago)
Oh, and for the ppm question I have no clue why I went and calculated the % composition by mass for both solutions. You think it's okay?
I thought it was a hard paper, there were no easy questions like definitions or drawing apparatus, like there was normally on past papers..



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Original post by geor
No the question before where it said if you added something (i think it was h2so4) what would be the difference?


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I remember it vaguely, do you know more about what the question said?

I can't think from the top of my head.
Original post by metaltron
What were your thoughts on acid preventing the hydrolysis of bromine?


I wrote something like this, hope its correct

"Acidifying causes water to ionize, forming H+ and OH-.Therefore the concentration of water molecules decreases and the H+ concentration increases. The position of equilibrium moves to the left because of these effects so less bromine is hydrolyzed"
Original post by Londrinna
I thought it was a hard paper, there were no easy questions like definitions or drawing apparatus, like there was normally on past papers..



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I think the paper was a very fair one. There were more recall questions than other papers. When I mean recall, I mean stuff like tests for compounds. Chemical equations etc
Original post by Londrinna
I thought it was a hard paper, there were no easy questions like definitions or drawing apparatus, like there was normally on past papers..

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Yes but many of the questions was repeated from the past papers. eg the accuracy and reliability of the titration.
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Original post by geor
No the question before where it said if you added something (i think it was h2so4) what would be the difference?


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Would react with barium to make barium sulfate (white precipitate) with magnesium to make magnesium sulfate (soluble) no change observed
I hope you guys put state symbols for some of the chemical equations you had to write out. There were two questions that asked for state symbols!
Okay guys so i think the paper was harder than previous ones specially the MCQS. But i hope i didnt lose more than 6-7 marks maximum. starting with mcqs i wrote SF6 , CCl4, 2-chlorobutane. for increasing covalent characer i said NaCl, MgCl2 to SiCl4. then for sodium chloride solubility i chose the hydration enthalpy one that was most appropriate.
then for the mass spectrum with 43,57,58 i chose propanone. i chose ozone sepletion for last one. volume calculation was the first option if i am not wrong

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