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Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

Reply 1940

Can some one please tell me how to do jan 12 q21bii? On what basis do we select the metal?

Step 1 shows Cr3+ going to Cr2+

So that should be one half equation.

Use your data booklet to find a half equation involving Cr3+ and Cr2+.

The second half equation should involve a metal, by which when you combine the two half equations, you get a positive E cell, hence making it a feasible reaction.

Reply 1941

AT95

So u mean we can take any value that is more negative than the value for Cr3+??

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Reply 1942

jojo1995

2

Original post by SuziieB

Am I the only one who genuinely prefers Unit 4 over Unit 5? I can't stand this unit.

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im the sAme

Reply 1943

F1's Finest

21

Original post by AT95

So u mean we can take any value that is more negative than the value for Cr3+??

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Yeah but it has to be a metal. Read the question carefully.

Reply 1944

AT95

Original post by James A

Step 1 shows Cr3+ going to Cr2+

So that should be one half equation.

Use your data booklet to find a half equation involving Cr3+ and Cr2+.

The second half equation should involve a metal, by which when you combine the two half equations, you get a positive E cell, hence making it a feasible reaction.

Oh, but the MS says we can take Zn as well but the Ecell for that would be -0.02 then. God this isnt making sense :facepalm:

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Reply 1945

F1's Finest

21

Original post by AT95

Oh, but the MS says we can take Zn as well but the Ecell for that would be -0.02 then. God this isnt making sense :facepalm:

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No, you've done the wrong working out.

The ms clearly says next to Zn '0.35', so that's the value you should have obtained when combining the two half equations.

Remember the metal (in it's solid state) and Cr3+ has to be on the left hand side of the overall equation when you combine then.

Reply 1946

posthumus

20

Ah I over slept :frown:

This exam is going to brutal.... still needa learn the separating techniques & complex reactions/colours ! -______-

Reply 1947

AT95

Original post by James A

No, you've done the wrong working out.

The ms clearly says next to Zn '0.35', so that's the value you should have obtained when combining the two half equations.

Remember the metal (in it's solid state) and Cr3+ has to be on the left hand side of the overall equation when you combine then.

Can you PLEASEEEE show me the working? :dontknow:

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Reply 1948

AtomicMan

13

If a burette reads to the nearest 0.05cm3, you get a result of say 10.00cm3. So the titire could be either 10.025cm3 or 9.975cm3. Is the uncertainty +-0.025cm3 and error +-0.05cm3, or are the error and uncertainties the same? Or the other way around? Really confused :s

Reply 1949

jojo1995

2

Original post by AtomicMan

If a burette reads to the nearest 0.05cm3, you get a result of say 10.00cm3. So the titire could be either 10.025cm3 or 9.975cm3. Is the uncertainty +-0.025cm3 and error +-0.05cm3, or are the error and uncertainties the same? Or the other way around? Really confused :s

I thought they were both the same. I agree with the 10.025 and 9.975 so error/ unvertainty is -or+ o.25 so is o.25x2/10.00 x 100

Reply 1950

posthumus

20

I've only ever seen reagents for nitrobenzene to phenylamine being HCl & HNO3 conc.

But now I just saw you have to add NaOH to seperate the salt ? C6H5N3Cl ???!!!

Reply 1951

study beats

22

Lol those jokes were funny

Reply 1952

Gnome :)

2

Original post by posthumus

I've only ever seen reagents for nitrobenzene to phenylamine being HCl & HNO3 conc.

But now I just saw you have to add NaOH to seperate the salt ? C6H5N3Cl ???!!!

Yep- it's the same for the preparation of aliphatic amines too. The ammonium salt always forms first, so you use NaOH to liberate the amine. So it's C6H5NO2 + conc HCl (+ Sn catalyst) --> C6H5NH3+Cl- , then adding NaOH forms C6H5NH2 + H2O + Cl-

(edited 10 years ago)

Reply 1953

«WD»ddd

Original post by SuziieB

Am I the only one who genuinely prefers Unit 4 over Unit 5? I can't stand this unit.

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For a very good reason i feel much more comfortable with unit 4 than with unit 5 :redface:

Reply 1954

randyaloul

Good luck to all! I'd stop revising if I were you, don't want to over-cram your brain before the exam directly.

Reply 1955

ChooChooCherry

good morning all! wishing everyone the best of luck, including myself! *cries*

Best of luck brahs

Good luck all- I'm off to college now, gonna give me some time to try and cram all the complex ion colours D: A few hours and it'll all be over, and unless you did something silly like apply for chem at uni (WHY?!?!?) then you'll never have to do any of this ever again :smile:

Reply 1958

AS01

12

Good luck everyone! Hopefully everything goes well!

Reply 1959

F1's Finest

21

Hi everyone, the exam went really well.
Firstly, for the multiple choice question which asked you to select which reaction produced a polyamide, did you put answer b or answer d? It was either one of them.

The second multiple choice which said about a hydrocarbon was burnt and they gave you values. Did you put down C3H8? I think that was answer b. I took a guess on it.

Okay and um the electrode potentials at the start of section B, because one of the questions told you to select two half cells and combine them, which ones out of the four did you choose? Bearing in mind the question said it has to be in alkaline. I used the two half cells which had OH- somewhere in them, so I used 2 and 4 and combined them.

For section C on the titration, did anyone get 1.8moldm-3 for the Titanium (IV) Chloride concentration?

Also for the next question which was the last one, I said some of the Titanium Chloride is readily oxidized by oxygen in the air, hence less TiCl4 is available in the titration.

Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

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