Author Topic: chem mcq questions  (Read 1841 times)

Offline ayesha.

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chem mcq questions
« on: June 09, 2010, 01:05:22 pm »
can anyone explain why the answer to q1 in o/n/02 is c?

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #1 on: June 09, 2010, 01:19:54 pm »
im using the formulae CxHy+ (x+y/4)O2 = xCO2 + Y/2H20

so in this case only CxHy = xCO2 is viable

methane is 1 c and ethane is 2 carbon. there fore CO2 must = 3 moles overall.

10 cm cube methane gives 10 cube  co2
10cm cue ethane gives 20 cm cube c02

total =30 cm cube

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #2 on: June 09, 2010, 01:21:08 pm »
hope that helps ;D

Offline aldehyde

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Re: chem mcq questions
« Reply #3 on: June 09, 2010, 01:21:48 pm »
1 mole of ch4=1 mole of co2= 10 cm3 of gas
1 mole of c2h5=2 mole of co2=20cm3 of gas
                                             ----------------
total volume of residual gas=20+10=30 cm3

Offline aldehyde

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Re: chem mcq questions
« Reply #4 on: June 09, 2010, 01:22:58 pm »
ooops i was a bit late anyway the first answer is better

Offline ayesha.

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Re: chem mcq questions
« Reply #5 on: June 09, 2010, 01:30:13 pm »
Thanks question 9 same paper

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #6 on: June 09, 2010, 01:32:48 pm »
yo react they both have to be in gaseous state and ions. this is has to be c gas and 0 atom not 02 because 02 is molecule

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #7 on: June 09, 2010, 01:33:11 pm »
bring on the next one =) ;D

Offline ayesha.

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Re: chem mcq questions
« Reply #8 on: June 09, 2010, 01:36:03 pm »
yeah but isnt formation when 1 mol of a substance is formed from its elements  in their standard state...so isnt oxygens standard state o2?

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #9 on: June 09, 2010, 01:44:18 pm »
im afraid not,

umm ok think of it this way formation is O2 is a molecule which means all of its bondong for both atoms are used . so where is carbon going to join ? but if you have o alone, then you get co which is not what you want .so its 2 O .

technically O in element form or standard state is O thats why O2 is not in the periodic table only O. its theory based. But in reality or practically O2 exists as a molecule. consider sulphur and phosphorous. they two are stated as p and s and not p4 and s8 which is what it really exists as

Offline ayesha.

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Re: chem mcq questions
« Reply #10 on: June 09, 2010, 02:14:44 pm »
thnk you !

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #11 on: June 09, 2010, 02:23:59 pm »
 ;D

Offline highly_ambitious

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Re: chem mcq questions
« Reply #12 on: June 09, 2010, 02:27:01 pm »
m/j 2008 qn 6 and 10...plz

Offline CHEMMASTER6000

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Re: chem mcq questions
« Reply #13 on: June 09, 2010, 02:32:29 pm »
not sure about 6 will furthus contemplate later.

but for 10 : basically you draw a hess cycle to stated formation of tio2 = =-940 and formation of c0 is -110
but there is 2 co

so using hess cycle you should get the number -(-940)+ 2(-110)= +740
« Last Edit: June 09, 2010, 03:00:20 pm by CHEMMASTER6000 »

Offline highly_ambitious

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Re: chem mcq questions
« Reply #14 on: June 09, 2010, 02:57:13 pm »
but the answer is +720