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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 268520 times)

Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1290 on: June 12, 2011, 04:30:04 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 04:01:09 pm
*Chem 4 June 2010 doubts:

Q19 ai & b

Q 19 ai) - You have tried doing it, yeah?

Kp= P CH3COOH/ P CH3OH X P CO

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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1291 on: June 12, 2011, 04:32:23 pm »
Quote from: Amelia on June 12, 2011, 04:30:04 pm
Q 19 ai) - You have tried doing it, yeah?

Kp= P CH3COOH/ P CH3OH X P CO



Yes, I have tried! :D

But, I didn't get how to do it! :S

Plus, That Q18 . . . I still don't get why can't the answer be A! :/
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1292 on: June 12, 2011, 04:40:45 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 04:32:23 pm
Yes, I have tried! :D

But, I didn't get how to do it! :S

Now you do, yes? Partial pressure of the products divided by the partial pressure of the reactants. Don't forget the units. Here it will be atm-1

As for the B part, try doing it yourself first.. Find the no. of moles at equilibrium. (93.6% of 50 moles gives the no. of moles for CH3COOH), then find the mole fraction due to each of the molecules. Then the partial pressure, and Kp.

Quote
Plus, That Q18 . . . I still don't get why can't the answer be A! :/

A is the result of ethane 1,2-diol + benzene-1,4-dicarboxylic acid + (another) ethane-1,2-diol...while,
C is just ethane 1,2-diol + benzene-1,4-carboxylic acid - this forms the repeat unit.

Do you get it, now?
« Last Edit: June 12, 2011, 04:55:47 pm by Amelia »
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1293 on: June 12, 2011, 04:54:46 pm »
Quote from: Amelia on June 12, 2011, 04:40:45 pm
Now you do, yes? Partial pressure of the products divided by the partial pressure of the reactants. Don't forget the units. Here it will be atm-1

A is the result of ethane 1,2-diol + benzene-1,4-dicarboxylic acid + (another) ethane-1,2-diol...while,
C is just ethane 1,2-diol + benzene-1,4-carboxylic acid - this forms the repeat unit.

Do you get it, now?


Yes! Thanks muchos! :D
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1294 on: June 12, 2011, 04:56:50 pm »
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1295 on: June 12, 2011, 05:00:48 pm »
I will practice them all over again now! :D

JazakAllah khair! :D
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Offline hkhkhk119

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1296 on: June 14, 2011, 09:16:15 am »
I wanna ask what is the difference between High Ea and the reaction not spontaneous(delta S =-ve)?
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Offline studz

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1297 on: June 14, 2011, 10:52:12 am »
can anyone give me a link to download the formula booklet?
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Offline studz

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1298 on: June 14, 2011, 11:03:24 am »
k nevermind i got it
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1299 on: June 14, 2011, 11:13:37 am »
Quote from: hkhkhk119 on June 14, 2011, 09:16:15 am
I wanna ask what is the difference between High Ea and the reaction not spontaneous(delta S =-ve)?

@hkhkhk119- Reaction is not spontaneous when delta S total is negative.

High activation energy indicates reactants are kinetically inert/kinetically stable.

@studz- I was gonna link you right now! Haha! Good you got it! :)
« Last Edit: June 14, 2011, 11:18:01 am by Romeesa Chan »
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1300 on: June 14, 2011, 11:47:27 am »
Quote from: Amelia on June 12, 2011, 03:46:53 pm
I hope I've got the right questions.  :P

Q10) Titration of strong base and strong acid.

 (a) What was the pH when 24.95 cm3  of 1.00 mol dm–3  NaOH(aq) had been added to 25 cm3  of 1.00 mol dm–3  HCl(aq)?

Ans is A. The volume of  NaOH added is less then the volume of acid. So, the solution is still acidic. The pH only falls very slightly until its quite near the "equivalence point".

(b) What was the pH when 25.05 cm3 of 1.00 mol dm–3  NaOH(aq) had been added to 25 cm3  of 1.00 mol dm–3  HCl(aq)?

Ans is D. The volume of alkali is here is more then the volume of acid. More OH ions in the solution, so higher pH.

(c) Which one of the following indicators would be MOST suitable to use to determine the end point of this titration?  
                                      pH range
A methyl violet  0-1.6
B universal Indicator 3-11
C  thymolphthalein 8.3-10.6
D alizarin yellow R 10.1-13.0

C. As the pH range shows this indicator is a weak acid, it can easily change color when the hydroxide ions are added and the end point is reached.

I am sorry to bother you but I don't understand part (c).

Isn't the titration between a strong acid and a strong base which has a end point range between 4 to 10.

So, isn't it suppose to be B? :S
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Offline studz

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1301 on: June 14, 2011, 12:12:11 pm »
lol romessa i saved u the trouble and time then :P you are welcome  ;) :D
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Offline wakemeup

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1302 on: June 14, 2011, 03:07:19 pm »
Quote from: Romeesa Chan on June 14, 2011, 11:47:27 am
I am sorry to bother you but I don't understand part (c).

Isn't the titration between a strong acid and a strong base which has a end point range between 4 to 10.

So, isn't it suppose to be B? :S

We need an indicator that will change it's colour at or near to the equivalence point. Universal indicator might change it's colour way before the equivalence point, so it is not suitable. The closest range we have to the equivalence point i.e 7 is in thymolphthalein, so it is the most suitable.
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1303 on: June 14, 2011, 03:31:01 pm »
Quote from: wakemeup on June 14, 2011, 03:07:19 pm
We need an indicator that will change it's colour at or near to the equivalence point. Universal indicator might change it's colour way before the equivalence point, so it is not suitable. The closest range we have to the equivalence point i.e 7 is in thymolphthalein, so it is the most suitable.
I got it and was gonna delete my post. Thanks muchos! ;)
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1304 on: June 14, 2011, 03:47:07 pm »
Unit 4 Sample paper- question 18ciii & iv.
Please urgent!
« Last Edit: June 14, 2011, 03:58:50 pm by Romeesa Chan »
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