Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 268751 times)

Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1155 on: May 23, 2011, 05:13:32 pm »
Indeed memories ..
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1156 on: May 23, 2011, 05:16:19 pm »
aw..:)

Do u guys mind if I ask, where is that member as in she/he left the forum or what?
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1157 on: May 23, 2011, 05:20:15 pm »
aw..:)

Do u guys mind if I ask, where is that member as in she/he left the forum or what?

She left but she says she might come back for a while in August.

Here ; https://studentforums.biz/profile/lolo93/ 
Verily, in the remembrance of Allah do hearts find rest(13:28)

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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1158 on: May 23, 2011, 05:26:40 pm »
She left but she says she might come back for a while in August.

Here ; https://studentforums.biz/profile/lolo93/ 

Aw..Hopefully since u guys miss her too much :) I think we have one thing in common *Hope* lol..
How was ur exam today?

Eh..am I somehow violating the purpose (chemistry doubts) of this thread  ::)..?
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1159 on: May 23, 2011, 05:31:38 pm »
Okay..Back to doubts :D

If a balance accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?

Shouldn't it be 0.02%
In ms they multiplied 0.05 by 2, why is that so? u aren't taking 2 readings :S
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1160 on: May 23, 2011, 05:34:01 pm »
Okay..Back to doubts :D

If a balance accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?

Shouldn't it be 0.02%
In ms they multiplied 0.05 by 2, why is that so? u aren't taking 2 readings :S

you are taking TWO readings , mass of ethanol the before burning and mass of ethanol after burning ;)
« Last Edit: May 23, 2011, 05:36:14 pm by ~ The Golden Girl ~ »
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1161 on: May 23, 2011, 05:36:18 pm »
^ Oh Thx

and one more

20 cm3 of sulfuric acid, concentration 0.25 mol dm–3, was neutralized in a titration with barium hydroxide, concentration 0.50 mol dm–3. The equation for the reaction is
Ba(OH)2(aq) + H2SO4(aq) ? BaSO4(s) + 2H2O(l)

(b) During the titration, the barium hydroxide was added until it was present in excess. The electrical conductivity of the titration mixture

A increased steadily.
B decreased steadily.
C increased and then decreased.
D decreased and then increased.
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1162 on: May 23, 2011, 05:37:47 pm »
^ Oh Thx

and one more

20 cm3 of sulfuric acid, concentration 0.25 mol dm–3, was neutralized in a titration with barium hydroxide, concentration 0.50 mol dm–3. The equation for the reaction is
Ba(OH)2(aq) + H2SO4(aq) ? BaSO4(s) + 2H2O(l)

(b) During the titration, the barium hydroxide was added until it was present in excess. The electrical conductivity of the titration mixture

A increased steadily.
B decreased steadily.
C increased and then decreased.
D decreased and then increased.

I don't remember Questions so tell me which paper is that and what Question :)
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1163 on: May 23, 2011, 05:39:38 pm »
I don't remember Questions so tell me which paper is that and what Question :)
Its Q10 from 2010 Jan
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1164 on: May 23, 2011, 05:47:07 pm »
Its Q10 from 2010 Jan

It's D ,Because 

This is a neutralization reaction and ususally neautralization reactions have LOWEST  conductivity which is why it decreases but then the barium hydroxide and sulfuric acid  react there are ions present and hence electric conductivity increases.

Ihmm 'll confirm the answer and then get back to you
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1165 on: May 23, 2011, 06:34:59 pm »
It's D ,Because 

This is a neutralization reaction and ususally neautralization reactions have LOWEST  conductivity which is why it decreases but then the barium hydroxide and sulfuric acid  react there are ions present and hence electric conductivity increases.

Ihmm 'll confirm the answer and then get back to you


I'm sorry for taking too long , I had to call my friend for this.

Hmm it's an follows as Nobody said ;

Look, initially, you've got H2SO4(aq) giving 3 ions
now, when you add barium hydroxide, it will form a precipitate and take out all the sulphate ions in the form of BaSO4(s) and further neutralise the hydrogen ions which fill form 2H2O(l).
oaky? so, at that time, the conductivity decreases.

Now, when all the sulfuric acid is neutralized... barium ions and hydroxide ions will be generated when Ba(OH)2(aq) reacts.
which will lead to an increase in the conductivity.



My friend's/teacher's explanation ;

as bRIUM HYDROXIDE IS added it's ions eat up the acid ions. hence no ions , cuz all ions cancel each other , electrical conductivity falls  to 0 ..On more addition of bariium hydroxide , OH- increases , i.e.e the -ve charge increases , hence electrical conductivity increases .

GG :)
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Offline Malak

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1166 on: May 23, 2011, 06:38:26 pm »
^ Oh I get it now..

Thankyou very much :)
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1167 on: May 23, 2011, 07:08:22 pm »
Welcome :)
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Offline ~ Miss Relina ~

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1168 on: May 23, 2011, 08:57:05 pm »
 >:( :( :'( unit 1
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Offline NightHawkerr

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1169 on: May 23, 2011, 10:06:41 pm »