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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 253173 times)

Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #705 on: January 09, 2011, 12:44:02 pm »
Quote from: Uchia on January 09, 2011, 06:34:56 am
cool I just did AS last june and it was pretty easy

All the best for your A2, then. :)
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #706 on: January 10, 2011, 08:43:18 am »
thanks and for you 2 if ur doing any other subject
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #707 on: January 12, 2011, 01:53:20 pm »
Just confused with this..

Which values of Lattice enthalpy assumes that a model is purely ionic
Theoretical or Experimental(Born-haber) ??

Thx
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Offline Weaam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #708 on: January 12, 2011, 02:08:05 pm »
Quote from: ang3l on January 12, 2011, 01:53:20 pm
Just confused with this..

Which values of Lattice enthalpy assumes that a model is purely ionic
Theoretical or Experimental(Born-haber) ??

Thx
Theoretical, i think.
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Offline Weaam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #709 on: January 12, 2011, 02:09:45 pm »
Can someone please explain Question 10 in Section A of the June 2010 paper to me ?
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #710 on: January 12, 2011, 02:24:13 pm »
Quote from: Weaam on January 12, 2011, 02:08:05 pm
Theoretical, i think.
So Assuming that its purely ionic will result in a More exothermic value?
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Offline Weaam

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #711 on: January 12, 2011, 02:24:58 pm »
And question 15 in Section B part b)(ii) and (iii) in the same paperr
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #712 on: January 12, 2011, 02:28:16 pm »
Quote from: ang3l on January 12, 2011, 02:24:13 pm
So Assuming that its purely ionic will result in a More exothermic value?
No, actually, the theoritical values are always slightly less exothermic, check the past papers, they always have a question about that with the values of both so u can compare
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #713 on: January 12, 2011, 02:39:16 pm »
Quote from: Weaam on January 12, 2011, 02:24:58 pm
And question 15 in Section B part b)(ii) and (iii) in the same paperr

B(ii) Because of the difference in ionic radius

(iii) to find the concentration in ppm, the formula is C = (Mass of component / Mass of solution) * 1000000

Therefore, first we need to find the mass of calcium M = moles * Mr
Moles is given so Mass = 0.100 * 40 = 4 g

Usign the formula C = (4 / 1000g ) * 1000000
=4000 ppm
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #714 on: January 12, 2011, 02:50:00 pm »
Quote from: ang3l on January 12, 2011, 02:39:16 pm
B(ii) Because of the difference in ionic radius

(iii) to find the concentration in ppm, the formula is C = (Mass of component / Mass of solution) * 1000000

Therefore, first we need to find the mass of calcium M = moles * Mr
Moles is given so Mass = 0.100 * 40 = 4 g

Usign the formula C = (4 / 1000g ) * 1000000
=4000 ppm
Thankss
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #715 on: January 12, 2011, 03:02:27 pm »
How can you tell the difference?
i mean how can u tell wheter its Mean bond enthalpy or bond enthalpy

thx
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #716 on: January 12, 2011, 03:16:45 pm »
Quote from: ang3l on January 12, 2011, 03:02:27 pm
How can you tell the difference?
i mean how can u tell wheter its Mean bond enthalpy or bond enthalpy

thx
Bond enthalpy is when only one bond is broken, in this case only when one C-H bond is broken.
Mean bond enthalpy is when more than one bond is broken and the average is taken. In this case when 4 C-H bonds are broken and their average taken.
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #717 on: January 12, 2011, 03:44:31 pm »
Howcome is it Neon..
For me its coming out to be Fluorine :S
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #718 on: January 12, 2011, 04:35:41 pm »
Can anyone help with this Q
thx
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Offline xMilishax

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #719 on: January 12, 2011, 05:02:14 pm »
Quote from: Weaam on January 12, 2011, 02:09:45 pm
Can someone please explain Question 10 in Section A of the June 2010 paper to me ?

It's C because first you find the number of moles of each of the solution by n = c x v then multiply the number of ions into the number of moles (n). A and B have 2 ions so x 2. C and D have 3 ions so x 3. A, B and D have the final answer = 2 but C = 3 so the answer is C.  Hope you understand. :)
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