IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: ayesha. on June 09, 2010, 01:05:22 pm
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can anyone explain why the answer to q1 in o/n/02 is c?
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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
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hope that helps ;D
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1 mole of ch4=1 mole of co2= 10 cm3 of gas
1 mole of c2h5=2 mole of co2=20cm3 of gas
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total volume of residual gas=20+10=30 cm3
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ooops i was a bit late anyway the first answer is better
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Thanks question 9 same paper
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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
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bring on the next one =) ;D
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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?
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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
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thnk you !
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;D
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m/j 2008 qn 6 and 10...plz
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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
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but the answer is +720
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sorry i mean +720 =)
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o/n/02 q 20 how is it addition?
By the way Thanks for all the help +rep
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no probs, last exam of colledge to excited and cant sleep anyways hahah. :P
anyhow this is application i think . its a different salt although its an aldehyde. im not sure why but if you think about it logically its not elimination cause double bond not form and its not substituition either cause nothing is lost . two of the same thing added together form a polymer which has the same number of carbon and oxygen and hydrogen . if anything it could be addition polymerisation but thats A2. anyhow so you can deduce its only addition .
in the second part a double bond is orm so clearly is elimination ;D
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m/j/03 q8