Chemistry: Post your doubts here!

[Jaf]

Tell me about it, I frequently use concepts of Bio in Chemistry (and vice versa), as well as using concepts of physics in maths (and vice versa).
But my argument still stands: when CIE sets questions they consider all the possible responses. Wouldn't they be aware of the fact that there is a probability that some candidates may think in terms of carbonic acid?
Which brings me to my next point: if what has been said above is true, then my theory of CaCO3 is false.
So what is the correct answer.
And again, the syllabus does not assume you know Bio, so stop explaining in those terms. I don't care if lactic acid is present in your buccal cavity; for all I know there could be traces of carbonic acid in the food we eat, that ever occur to you?

This will lead us no where. Never has an endorsed chemistry book mentioned carbonic acid nor do we need to know about its chemistry. Like I said, chances of you having carbonic acid in your mouth are slim to none. (the reaction is very slow and you need an enzyme to make CO2 react with H2O).
Therefore, by intuitively considering the basic mineral and organic acids we come across in our course, 3 is not true.

So unless you come up with a more valid point to defend the flimsy carbonic acid argument, any discussion will be futile.

 

[roadtrip9o9]

jaf solve these PLEASE http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf 11,13,16,22,23,26,28,28,30,32,35,40

 

[roadtrip9o9]

anyone ?

 

[namename]

Can anyone please tell me why the mark scheme for w09 p4 4c) for alkaline aqueous iodine (I2 +OH-) and mark scheme for w10 p42 5b) iv) are contradicting??
Does a phenol have reaction w/ I2+OH- ??

 

[roadtrip9o9]

solve these http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf 11,13,16,22,23,26,28,28,30,32,35,40

 

[namename]

Hey please help question b)
I'm quite sure Ecell = Ereduction - Eoxidation
then it becomes -0.83-1.23 = -2.86V and -0.83 -1.36 = -2.19V

However the ms says +2.86V and +2.19V
why is it so?

does Ecell becomes reversed for electrolysis?

 

[salmank]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q.9,, 37,, 40??

 

[farrukh]

How do we know from the structure the compund is 1 4 di substituded arene as ms says???please reply ASAP

 

[Scafalon40]

This will lead us no where. Never has an endorsed chemistry book mentioned carbonic acid nor do we need to know about its chemistry. Like I said, chances of you having carbonic acid in your mouth are slim to none. (the reaction is very slow and you need an enzyme to make CO2 react with H2O).
Therefore, by intuitively considering the basic mineral and organic acids we come across in our course, 3 is not true.

So unless you come up with a more valid point to defend the flimsy carbonic acid argument, any discussion will be futile.

I still don't understand why you choose to defend you "biological" explanation. I thought the question was about equilibria, but instead of explaining in those terms you choose to do it a totally different way i.e "chemistry doesn't apply here, this is all biology". If that is the case I would sit in my chemistry exam with the chapter 'anatomy of the heart' prepared, or maybe even 'the formula for the coefficient of friction' prepared.
If you can't explain that question in simple terms, without relating to some chapter in your 'endorsed' biology book which your examiner is apparently examining you from, then I'm afraid you are right: this discussion is pointless, unless you can explain it in other terms.
And I am at a loss at explaining why you don't know what carbonic acid is, there are only a handful of acids we ever come across in our course, and surely you must have heard the name.
And why would you go off and call somebody's argument 'flimsy' just because you are trying to defend a totally baseless claim that the examiners will test you on something you are not expected to know?
You don't need answer that question now, it's apparent you don't have a valid argument.

 

[saudha]

Number of gas moles on the left hand side is 1.
Number of gas moles on the right hand side is 2.
Increasing the pressure favors backward reaction (so yield of propan-2-ol increases, yield of propanone and hydrogen decreases)

i guess tht explains my doubt....... thxx a lot

 

[raiyanfarrukh]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
Hi if anyone could help me with qno. 3?? thanxx

 

[xhizors]

how B is the right answer
s05

 

[leosco1995]

B is right because all of the other 3 diagrams are wrong. In A, the bond length increases because the bond energies decrease. In C, the B.P increases with increasing # of electrons. And D is wrong because the HX energies decrease (you can even check this in the data booklet).

...

And B is right because the # of Van Der Waal forces increase with increasing electrons.

 

[Jaf]

I still don't understand why you choose to defend you "biological" explanation. I thought the question was about equilibria, but instead of explaining in those terms you choose to do it a totally different way i.e "chemistry doesn't apply here, this is all biology". If that is the case I would sit in my chemistry exam with the chapter 'anatomy of the heart' prepared, or maybe even 'the formula for the coefficient of friction' prepared.
If you can't explain that question in simple terms, without relating to some chapter in your 'endorsed' biology book which your examiner is apparently examining you from, then I'm afraid you are right: this discussion is pointless, unless you can explain it in other terms.
And I am at a loss at explaining why you don't know what carbonic acid is, there are only a handful of acids we ever come across in our course, and surely you must have heard the name.
And why would you go off and call somebody's argument 'flimsy' just because you are trying to defend a totally baseless claim that the examiners will test you on something you are not expected to know?
You don't need answer that question now, it's apparent you don't have a valid argument.

So we'll just have to agree to disagree. That's fine.

 

[leosco1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
Hi if anyone could help me with qno. 3?? thanxx

I am not sure if this is the right way to solve it, but I got the right answer with it so..

C6H12 + 9O2 -> 6CO2 + 6H2O

So you have 6 moles of CO2 and 6 moles of H2O. P will absorb all of the mass of H2O, while Q will absorb of all of the mass of CO2. Their masses are 6(18) and 6(44) respectively, and the ratio will give you 18/44 = 0.41.

 

[leosco1995]

What are the bond angles in the PH3 molecule likely to be?
A) 90
B) 104
C) 109
D) 120

Question is Q7 from Winter 2004, http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_er.pdf

PH3 has 3 bonds and 1 lone pair, so I thought the bond angle would be 109. But the answer is 104, why is that?

 

[Brains]

HOW DO YOU KNOW IF A MOLECULE IS PLANAR OR NOT??? eg:for CO2, PCL5, ethane, ethene, NH3 (AS)




REPLY PLZ!

 

[Brains]

What are the bond angles in the PH3 molecule likely to be?
A) 90
B) 104
C) 107
D) 120

Question is Q7 from Winter 2004, http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_er.pdf

PH3 has 3 bonds and 1 lone pair, so I thought the bond angle would be 109. But the answer is 104, why is that?

for every loan pair the bond angle decreases by 2.5 degree.

 

[Scafalon40]

So we'll just have to agree to disagree. That's fine.

Fine by me.

 

[leosco1995]

Yeah, you are right. Actually, my teacher told me that 3 bonds and 1 lone pair are approximately 107, and since B and C were quite close to each other I thought C would be correct. Confusing question IMO.