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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 268532 times)

Offline Assi1993

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1275 on: June 07, 2011, 03:41:46 am »
how and how can i kill chemistry??? dnt knw wht m gna doooo 2day!!!!!!! Plzz pray for me
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Offline NotAbod

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1276 on: June 07, 2011, 03:46:22 am »
Okay, First off, revise everything! and solve if you still have enough time, but if only 3-8 hours are left, then keep revising, and don't waste your time in solving. what you can't memorise, write it, till you learn it. ;D :)
Good Luck.
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Offline Assi1993

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1277 on: June 09, 2011, 12:15:42 am »
Quote from: AboD on June 07, 2011, 03:46:22 am
Okay, First off, revise everything! and solve if you still have enough time, but if only 3-8 hours are left, then keep revising, and don't waste your time in solving. what you can't memorise, write it, till you learn it. ;D :)
Good Luck.

:) thanks ..i will not forget this peice of advice ;)
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1278 on: June 12, 2011, 02:59:51 pm »
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1279 on: June 12, 2011, 03:44:06 pm »
*Chem 4 Jan 2010 doubts:

Q3, Q18 and Q20
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1280 on: June 12, 2011, 03:46:53 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 02:59:51 pm
*Chem 4 [sample paper] doubts:

Q10 and Q12b



http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/sam-gce-chemistry.pdf

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.
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1281 on: June 12, 2011, 03:53:43 pm »
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.

JazakAllah khair! :D
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Offline EMO123

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1282 on: June 12, 2011, 03:56:01 pm »
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1283 on: June 12, 2011, 03:57:38 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 03:44:06 pm
*Chem 4 Jan 2010 doubts:

Q3, Q18 and Q20

Q3 - Ans. is B. About phenolphthalein -  the weak acid is colourless and its ion is bright pink. Adding extra hydrogen ions shifts the position of equilibrium to the left, and turns the indicator colourless. Adding hydroxide ions removes the hydrogen ions from the equilibrium which tips to the right to replace them - turning the indicator pink.
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1284 on: June 12, 2011, 04:01:09 pm »
*Chem 4 June 2010 doubts:

Q19 ai & b
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1285 on: June 12, 2011, 04:04:13 pm »
Quote from: EMO123 on June 12, 2011, 03:56:01 pm
means what

Phrase that people use to thank others. It literally means 'May Allah grant you goodness'.

:)
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Offline EMO123

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1286 on: June 12, 2011, 04:05:33 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 04:04:13 pm
Phrase that people use to thank others. It literally means 'May Allah grant you goodness'.

:)
wow only a short phrase with a long meaning
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1287 on: June 12, 2011, 04:10:09 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 03:44:06 pm
*Chem 4 Jan 2010 doubts:

Q3, Q18 and Q20

Q 18 - Ans. is A. Draw both the molecules first.. then, delete H2O from both sides.  ::) (I'm sure you wont get it, but try  :P)

Q 20 - Ans. is C. The disassociation is endothermic. And Kw increases as the temperature increases, so more H+ at higher temperature.
« Last Edit: June 12, 2011, 04:17:57 pm by Amelia »
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Offline Romeesa-Chan

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1288 on: June 12, 2011, 04:14:18 pm »
Quote from: Amelia on June 12, 2011, 04:10:09 pm
Q 18 - Ans. is A. Draw both the molecules first.. then, delete H2O from both sides.  ::) (I'm sure you wont get it, but try  :P)



=.= I thought of A too! But, according to MS it is C. >,<
« Last Edit: June 12, 2011, 04:19:58 pm by B.L.O.S.S.O.M. »
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Amelia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #1289 on: June 12, 2011, 04:20:26 pm »
Quote from: B.L.O.S.S.O.M. on June 12, 2011, 04:14:18 pm
=.= I thought of A too! But, according to MS it is C. >,<

LOL! I'm sorry. Yes, it must be C, because they have asked for just one repeat unit. This unit will repeat itself to form the polyster.

'A' is right, but it's one unit and half. ::)
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