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Chemistry: Post your doubts here!

D

Doctor Nemo

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Ahmed Ali Akbar said:
help needed in mcq 6,8,27 of may june 08....
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For 6 I can only get the answer of 2.72 dm3 and the closest answer is 2.67 so I chose C which is correct. Just put the numbers into the ideal gas equation for 1/18 moles of H2O

101000 X V = .05555 X 8.31X 596 ----> V = 2.72 X 10-3 cubic meters or 2.72 dm3


8 is difficult and I don´t have time to explain all of the graphs. However A should be a graph for an inverse curve not a straight line. The other two are harder but for D in the equation PV = nRT if P is constant then V is directly proportional to T so D is correct.

27

Dehydration implies that the molecule is an alcohol, for it not to be susceptible to mild oxidizing agents then it must be a tertiary alcohol. So the -OH group is on the carbon next to ring that also has the methy group. Dehydration would produce molecule D.
 
D

Doctor Nemo

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Just call me MJ said:
Ok. a really annoying question that is repeated many times over is Question 6, paper 1, may/june 2002.....
I memorized it but I don't understand why O__o could somebody explain it please?!?!?!
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You again, good thing I have had some wine with my dinner.

OK the basic idea is that the two gases are independent of each other and the total pressure is simply equal to the sum of the pressure of each gas. You apply P1V1 =P2V2 to each gas separately. After the valve is open the volume is 3.

So 1 X 2 = P X 3 ----> P = 2/3

then 2 X 1 = P X 3 --- P = 2/3 just add the two pressures and the answer is 4/3 or 1and 1/3 which is A which is correct because I only answer questions to which I know the answer. Think about that for a moment. You better give me a like for this.
 
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hassam

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I is for competitve inhibition.....and II for non-competitive......why is rate for non-competitive higher than competitve but lower than normal....?
 

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omg

omg

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can i get the mark scheme ov nov 2011 p53 and p51!! its nt there in the paper sec!! pls i need it urgently
 
Just call me MJ

Just call me MJ

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hassam said:
I is for competitve inhibition.....and II for non-competitive......why is rate for non-competitive higher than competitive but lower than normal....?
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Both competitive and non competitive inhibit the reaction of the enzymes in one or more ways. the competitive inhibitors compete with the substrates for the active site of the enzyme, and once they enter the enzyme's active site, they act like substrates, and the other substrates have to "wait" for the inhibitors to be broken down, to replace them. thats why the reaction rate becomes constant for some time, and thats why its rate of reaction is almost half of that of the normal.

Non competitive inhibitors attach themselves to other parts of the enzyme, inhibiting its function in an indirect way, but the enzyme itself can still act on the substrate. because of the non competitive inhibitors the enzymes have a lower rate of reaction than that of the normal, since enzymes can't function at "full power" :) Makes sense?!? o_O
 
smzimran

smzimran

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Any notes regarding applications, anyone? It is not given very well in the application booklet.
 
abcde

abcde

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smzimran said:
I am very bad at rote-learning. :(
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Don't call it rote learning! Make notes, reference cards - basically anything that makes the content stick in your mind. Make it 'stick' not by rote-learning but by comprehension/understanding.
 
abcde

abcde

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smzimran

smzimran

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abcde said:
Don't call it rote learning! Make notes, reference cards - basically anything that makes the content stick in your mind. Make it 'stick' not by rote-learning but by comprehension/understanding.
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Hmmm.....:)
 
D

Doctor Nemo

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smzimran said:
Hmmm.....:)
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Sorry, I was being sarcastic. The Chemistry Applications booklet is rather poor. The newer version looks better and seems to have less excess material that you do not need to know. Make sure you are using that version.

Much of the material can be found in biology books for example. If you do not understand the material in the booklet then try reading about the same material in another book. It sometimes helps to read another version about the material.
 
smzimran

smzimran

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Doctor Nemo said:
Sorry, I was being sarcastic. The Chemistry Applications booklet is rather poor. The newer version looks better and seems to have less excess material that you do not need to know. Make sure you are using that version.

Much of the material can be found in biology books for example. If you do not understand the material in the booklet then try reading about the same material in another book. It sometimes helps to read another version about the material.
Click to expand...
I am using the latest one I suppose...and by the way, thanks
 
Just call me MJ

Just call me MJ

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Can somebody explain question 8 paper1 may/june 2003! Its soooooo annoying!! when you think you could answer 1 paper without a single mistake and you get the exact opposite!
 
Vogue

Vogue

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In a titration between an acid (in burette) and an alkali, you may need to re-use the same titration flask.
Which is the best procedure for rinsing the flask?
A. Rinse with distilled water and then with the alkali.
B. Rinse with tap water and then with distilled water
C. Rinse with tap water and then with the acid.
D. Rinse with the alkali.

and another question is dat how come many carbonates react with acids when all carbonates are insolube except ammonium, potassium and sodium.......?
 
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