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Author Topic: ALL CIE CHEMISTRY DOUBTS HERE !!  (Read 122969 times)

Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #600 on: May 30, 2011, 04:24:21 pm »
Quote from: Ari Ben Canaan on May 30, 2011, 03:28:19 pm
The question says 1cm3 of ice is heated.

Using the formula density = mass/volume you should be able to determine the mass of ice heated.

Next, you must realise that ice is basically water... Can you calculate the no. of moles of water in 1 gram of ice ? Should be easy.

Now, use the formula PV=nRT.

Rearrange for Volume. Remember the volume you calculate will be in m3 NOT dm3.

For this one, I got 2.72 instead of 2.67  :-[
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Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #601 on: May 30, 2011, 04:25:27 pm »
Quote from: Ari Ben Canaan on May 30, 2011, 03:33:37 pm
You should be able to eliminate two of the options straight away.

In this scenario, look for the carboxylic acid group.... COOH. Also, look for carbons with four different structures attached to them.



I understand it now.  :)
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"If A equals success, then the formula is:
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elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #602 on: May 30, 2011, 04:34:00 pm »
Quote from: $H00t!N& $t@r on May 30, 2011, 04:24:21 pm
For this one, I got 2.72 instead of 2.67  :-[

Yes, that's what I got too. The reason they put 2.67 is to probably test your confidence.
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Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #603 on: May 30, 2011, 04:37:32 pm »
Quote from: Ari Ben Canaan on May 30, 2011, 04:34:00 pm
Yes, that's what I got too. The reason they put 2.67 is to probably test your confidence.

ah i see..  :D
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"If A equals success, then the formula is:
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Offline SkyPilotage

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #604 on: May 30, 2011, 04:47:05 pm »
Quote from: Ari Ben Canaan on May 30, 2011, 04:34:00 pm
Yes, that's what I got too. The reason they put 2.67 is to probably test your confidence.
Hmm...Well There is another way to solve it...
-Its given that there are 24 dm3 in 298K
So whats the volume in 596K? Cross multiply to get 48 dm3...

-1 mole-------------->48 dm3  ( at 596K)
-X mole-------------->Y dm3   (at 596K)
To find out the number of moles of ice..We have the mass as 1g and molar mass as 18g..So cross-multiply to get 2.666666666666 dm3.....
I think using the PV=NRT doesnt give the exact answer since steam is NOT an ideal gas. :)
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Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #605 on: May 30, 2011, 08:11:28 pm »
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"If A equals success, then the formula is:
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elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #606 on: May 31, 2011, 06:01:05 am »
Quote from: $H00t!N& $t@r on May 30, 2011, 08:11:28 pm
i have another question.. Q28 October/November 2009 variant 12
http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w09_qp_12.pdf

Option B is correct since, when you draw it out (see below).

It is a rearrangement of the target molecule in the question. Just substitute the Br with a COOH group.



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Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #607 on: May 31, 2011, 08:37:57 am »
Quote from: Ari Ben Canaan on May 31, 2011, 06:01:05 am
Option B is correct since, when you draw it out (see below).

It is a rearrangement of the target molecule in the question. Just substitute the Br with a COOH group.





Thanks I get it  :)
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Offline $H00t!N& $t@r

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #608 on: May 31, 2011, 08:42:27 am »
« Last Edit: May 31, 2011, 12:06:32 pm by $H00t!N& $t@r »
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elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #609 on: May 31, 2011, 12:16:29 pm »
Question 11

Y is a product. Initially there is no Y present. What does this tell you about the concentration at t=0 ?

Similarily, what concentration of X is present at t=0 ? You should now be able to eliminate 2 out the 4 options.

When equilibrium has been reached [X(aq)] has fallen to 0.25mol dm–3

Using that statement can you not calculate the moles of X and Y present at equilibrium using the given equation ?

Now calculate the Kc... It should all come together.

Question 12

This is something simple that you should be well aware of. Read your textbook.

Question 40

I'll give you a hint. Think about SN1 reactions and the formation of a carbocation....
« Last Edit: May 31, 2011, 12:21:13 pm by Ari Ben Canaan »
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Offline Vin

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #610 on: May 31, 2011, 04:14:32 pm »
Score 0 of 1

Question:

A mass spectrum of magnesium shows three peaks at mass numbers 24, 25 and 26. The relative heights of these peaks are 60, 8 and 10 respectively. What is the mean atomic mass of Mg?

    Response:
    Wrong   

    24.1
    Should have chosen   

    24.8
       

    25.4
       

    25.0
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elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #611 on: May 31, 2011, 04:55:54 pm »
Are you sure this is the complete question ?
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Offline Vin

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #612 on: May 31, 2011, 06:09:31 pm »
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Offline SkyPilotage

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #613 on: May 31, 2011, 08:37:44 pm »
Quote from: Vin on May 31, 2011, 04:14:32 pm
Score 0 of 1

Question:

A mass spectrum of magnesium shows three peaks at mass numbers 24, 25 and 26. The relative heights of these peaks are 60, 8 and 10 respectively. What is the mean atomic mass of Mg?

    Response:
    Wrong   

    24.1
    Should have chosen   

    24.8
       

    25.4
       

    25.0
Well it should be done by 24x(60/78)+25x(8/78)+26x(10/78) But the answer is 24.4 :( Info should be enough to solve .... This question is similar to May June 2007 question 1....
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Offline Aadeez || Zafar

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #614 on: May 31, 2011, 08:45:08 pm »
Quote from: SkyPilotage on May 31, 2011, 08:37:44 pm
Well it should be done by 24x(60/78)+25x(8/78)+26x(10/78) But the answer is 24.4 :( Info should be enough to solve .... This question is similar to May June 2007 question 1....
i got it 24.35 and in the periodic tabel it is 24.3 , i think choosing the closest one would be best
and thus the ans would have been 24.1 as  it it is the closest to 24.35, see the examinaer REPORT, somtinh would be mentioned there
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