Author Topic: CHEM AND BIO HELP AND TIPS HERE  (Read 350929 times)

Offline rameeziiii

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2400 on: June 02, 2010, 04:01:50 pm »
the functional group is -COOH.... sometimes written as -CO2H... and how would that work? CnH2nO2? that would remove one the hydrogens...
« Last Edit: June 02, 2010, 04:04:05 pm by ahmediiii »

Offline basharooo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2401 on: June 02, 2010, 04:43:59 pm »
i have a quick question the formula for acids is cnh2n+1 cooh but i read that there is a new formula which works the same cnh2n o2 how can it be the same


the correct forumla of acid is Cn-1 H2n-1COOH

Offline basharooo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2402 on: June 02, 2010, 04:47:34 pm »
I have an important question and it is expected to come in the chemistry paper 3

-describe the use of hydrogen as a potential fuel reacting with oxygen to generate electricity in a fuel cell ??

is this is new ,, i never saw a quetion in the past papers about this topic, if there is any quetion in the pastpapers plz post it here !!

Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2403 on: June 02, 2010, 05:05:13 pm »

the correct forumla of acid is Cn-1 H2n-1COOH

I don't think there's a -1.  I think this is it:

CnH2n+1COOH
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nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2404 on: June 02, 2010, 05:06:39 pm »
I don't think there's a -1.  I think this is it:

CnH2n+1COOH

yup that's right.

Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2405 on: June 02, 2010, 05:07:58 pm »
I have an important question and it is expected to come in the chemistry paper 3

-describe the use of hydrogen as a potential fuel reacting with oxygen to generate electricity in a fuel cell ??

is this is new ,, i never saw a quetion in the past papers about this topic, if there is any quetion in the pastpapers plz post it here !!

There would not be any past paper questions for this particular topic as it is new for the 2010 syllabus (any new material for the 2010 syllabus is highlighted by black veritcal lines either side of the text.
Always willing to help!  8)
"In helping others, we shall help ourselves, for whatever good we give out completes the circle and comes back to us."

nid404

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2406 on: June 02, 2010, 05:11:14 pm »
I have an important question and it is expected to come in the chemistry paper 3

-describe the use of hydrogen as a potential fuel reacting with oxygen to generate electricity in a fuel cell ??

is this is new ,, i never saw a quetion in the past papers about this topic, if there is any quetion in the pastpapers plz post it here !!

It's a potential fuel cause it is non-polluting. The products of the reaction in the cell is water. It also has a high efficiency and requires less maintenance.  

Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2407 on: June 02, 2010, 05:15:46 pm »
There would not be any past paper questions for this particular topic as it is new for the 2010 syllabus (any new material for the 2010 syllabus is highlighted by black veritcal lines either side of the text.

Because the syllabus also says:
Quote
details of the construction and operation of a fuel cell are not required

I guess the key points you would need to know is:

1) A hydrogen-oxygen fuel cell produces only water as a product.

2) A hydrogen-oxygen fuel cell is efficient and non-polluting.

3) When a fuel cell is working, hydrogen loses electrons at the cathode and oxygen gains electrons at the anode.

Here's a nice diagram!  ;)
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Offline J.Darren

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2408 on: June 02, 2010, 06:29:11 pm »
There would not be any past paper questions for this particular topic as it is new for the 2010 syllabus (any new material for the 2010 syllabus is highlighted by black veritcal lines either side of the text.
... The IGCSE Chemistry Revision Guide, which was published in 2006 / 2007, has devoted a page to hydrogen fuel cells :o

Would it be considered as copyright infringement if I were to scan and upload that particular page ?
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holtadit

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2409 on: June 02, 2010, 06:30:19 pm »
... The IGCSE Chemistry Revision Guide, which was published in 2006 / 2007, has devoted a page to hydrogen fuel cells :o

Would it be considered as copyright infringement if I were to scan and upload that particular page ?

Nope ;)

Offline J.Darren

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2410 on: June 02, 2010, 07:00:23 pm »
Nope ;)
Hydrogen fuel cells

Advantages :

- Most energy rich (releases more energy per kg than any other conventional fuel)
- Only product of combustion is water
- Oxides of nitrogen are not produced

Disadvantages :

- Difficult to store
- Expensive to produce

H2 -> 2H+ + 2e-

O2 + 2H2O + 4e- -> 4OH-

H+ + OH- -> H2O

2H2 + O2 > 2H2O
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Offline sarasa

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2411 on: June 03, 2010, 12:59:30 am »
Because the syllabus also says:
I guess the key points you would need to know is:

1) A hydrogen-oxygen fuel cell produces only water as a product.

2) A hydrogen-oxygen fuel cell is efficient and non-polluting.

3) When a fuel cell is working, hydrogen loses electrons at the cathode and oxygen gains electrons at the anode.

Here's a nice diagram!  ;)
I believe u have reversed them, hydrogen at the anode nd oxygen at da cathode.
This is opposite of electrolysis. It's shown by ur diagram even...!

Offline Ivo

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2412 on: June 03, 2010, 01:36:29 am »
I believe u have reversed them, hydrogen at the anode nd oxygen at da cathode.
This is opposite of electrolysis. It's shown by ur diagram even...!

Hmm, I'm pretty sure reaction invovling hydrogen happens at cathode and likewise for oxygen at the anode.  I guess the diagram I chose was a bit weird, because if you look carefully, there are the - sign in hydrogen and + in oxygen.

My 'case' for this is also exemplified by this link:

http://inventors.about.com/od/sstartinventions/ss/Physics_Illustr_2.htm
« Last Edit: June 03, 2010, 01:38:05 am by Ivo »
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Offline Raywin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2413 on: June 03, 2010, 02:11:49 am »
I believe u have reversed them, hydrogen at the anode nd oxygen at da cathode.
This is opposite of electrolysis. It's shown by ur diagram even...!

See this diagram. I found it pretty good. :)
;D

Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2414 on: June 03, 2010, 06:35:00 am »
Guys a stupid doubt ... How to name this? I seriously forgot :-[