Chemistry: Post your doubts here!

[sidbloom1995]

can any1 answer this???
are HCl, HBr, HI strong acids in aqueous solutions??

HCl is a strong acid because it can be fully ionized
HBr and HI can also be fully ionized but compare to HCl they are weaker!!

 

[sidbloom1995]

I have a question > When we want to use Bond energy of Cl2 >> as its quoted in the
Data booklet it should be 242 .. but for Many time i have seen that they are using 244 as the answer !
Why? which data should we quote if the question came to us ?
one of the questions is o'n 2009 va' 41

TheZodiac
6Astarstudent

yes i came across that myself
just make sure that ur method is correct
the mark scheme is wrongly printed
i checked the previous data booklets and they also have 242
as long as ur procedure was correct u dont have to worry about the mark scheme using 244 instead of 242

 

[yousef]

yes i came across that myself
just make sure that ur method is correct
the mark scheme is wrongly printed
i checked the previous data booklets and they also have 242
as long as ur procedure was correct u dont have to worry about the mark scheme using 244 instead of 242

No bro , every year the values change !
so you get new data booklet every year , and make sure you use the value in the booklet you are given on the day of exam

 

[Browny]

Danial thanks for the help.
But in 36) why can't it be SO to SO3 and CO to CO2.
and in 35), is MgO insoluble.

 

[danial 234]

Danial thanks for the help.
But in 36) why can't it be SO to SO3 and CO to CO2.
and in 35), is MgO insoluble.

in 36) it cant be SO to SO3 and CO to CO2. cz these reactions dont occur spontaneously. in air...
in 35) MgO is very slightly soluble.

 

[williamcwz]

The cracking of a single hydrocarbon molecule, CnH2n+2, produces two hydrocarbon molecules only. Each hydrocarbon product contains the same number of carbon atoms in one molecule. Each hydrocarbon product has non-cyclic structural isomers.
What is the value of n?
A 4 B 6 C 8 D 9

 

[williamcwz]

An element X and compound YZ react separately with acid as shown.
X(s) + 2H+(aq) → X2+(aq) + H2(g) YZ(s) + 2H+(aq) → Y2+(aq) + H2Z(g)
When 1.0 g of either X or YZ is reacted with an excess of acid, the total volume of gas formed is
reacted with an excess of acid, the total volume of gas formed is the same.
Which statements are correct?
1 Ar(X) = Mr(YZ)
2 X and Y are metals.
3 X and Y must both be in the same Group of the Periodic Table.

 

[Igcse stuff]

Its not that difficult to score good marks in atleast P2 and P4 ...... For this you should be knowing each and everything thing of the syllabus on the fingre tips , concepts should be clear ...and then revising the stuff on regular intervals to ensure that u have retained all what u have prepared ...and then attempting past pprs (*the way u solve the ppr also counts a lot )and then finally discussing the things/doubts and all that with your teacher ...All these things will surely be contributing to get good marks and its very possible to get even full marks and in this way then u wont be having that much tension for either P3 or P5 and easily you can score A*.
P.s even if you get C's or D's in P3 or P5 and very high A grades in P1,2,4 even then you can get an overall A* .

Thanks a lot

 

[P1O2I3U4]

Can anyone help me with Paper 1, O/N 2003 Question 31. Why doesn't oxidation and reduction NOT occur?
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

 

[Ahmed Aqdam]

can any1 answer this???
are HCl, HBr, HI strong acids in aqueous solutions??

They all are strong acids and HI is the strongest of them, then HBr and HCl is weakest.

 

[Ahmed Aqdam]

The cracking of a single hydrocarbon molecule, CnH2n+2, produces two hydrocarbon molecules only. Each hydrocarbon product contains the same number of carbon atoms in one molecule. Each hydrocarbon product has non-cyclic structural isomers.
What is the value of n?
A 4 B 6 C 8 D 9

The value cannot be an odd number as then the two hydrocarbons could not have same number of carbon atoms. If n is 6 or smaller the alkene could have only 3 carbon atoms at most, so it would not have non-cyclic structural isomers. So C is the answer.

An element X and compound YZ react separately with acid as shown.
X(s) + 2H+(aq) → X2+(aq) + H2(g) YZ(s) + 2H+(aq) → Y2+(aq) + H2Z(g)
When 1.0 g of either X or YZ is reacted with an excess of acid, the total volume of gas formed is
reacted with an excess of acid, the total volume of gas formed is the same.
Which statements are correct?
1 Ar(X) = Mr(YZ)
2 X and Y are metals.
3 X and Y must both be in the same Group of the Periodic Table.

1. As equal volume of gas is produced by both X and YZ, their Ar and Mr should be same.
2.Metals react with acids to form salt and hydrogen gas. In the second reaction, metallic oxide is being reduced. So both X and Y are metals.
3.They could be Group 2 metals or transition metals.
So, the answer is B, 1 and 2 are correct.

Can anyone help me with Paper 1, O/N 2003 Question 31. Why doesn't oxidation and reduction NOT occur?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

Nitrogen remains -3 as in the ammonium ion the extra hydrogen results in a +1 charge on the ion.
Sulfur also remains +6 as the extra oxygen in the sulfate ion results in a -2 charge on the ion.
The charge on only the ions formed change and not on individual atoms.

 

[sidbloom1995]

how do we react H2O2 with KI and Cl2 with SO2 and form a redox equation using data from the data booklet?

 

[P1O2I3U4]

Nitrogen remains -3 as in the ammonium ion the extra hydrogen results in a +1 charge on the ion.
Sulfur also remains +6 as the extra oxygen in the sulfate ion results in a -2 charge on the ion.
The charge on only the ions formed change and not on individual atoms.

Thanks a lot

 

[sandwich147]

Hi guys! Can you help me with this questions? Thank you in advance

 

[hellangel1]

Please please someone tell me this, when writing stuctural formual do we show the C=O bond, like when writing structure of a ketone.. An examiner report says that we have to show this bond and other bonds like this..someone clarify please

 

[Suchal Riaz]

Please please someone tell me this, when writing stuctural formual do we show the C=O bond, like when writing structure of a ketone.. An examiner report says that we have to show this bond and other bonds like this..someone clarify please

If u are asked to draw structural formula and you draw this CH3COCH3. This is is same as drawing this:
CH3
>C=O
CH3
But if u are asked to draw 'display' formula then u must show all bonds especially C=O, C=C and triple bond in CN as well as simple C-C and C-H bonds.

 

[sitooon]

cathode: Pb(s) -----> Pb2+(aq) + 2e–
anode: PbO2(s) + 4H+(aq) + 2e–---> Pb2+(aq) + 2H2O(l)

By considering the effect of decreasing [Pb2+(aq)] on the electrode potentials of
the cathode and the anode, deduce the effect of the overall Ecell.
State whether the Ecell will increase, decrease or remain the same.
Explain your answer.

 

[hellangel1]

If u are asked to draw structural formula and you draw this CH3COCH3. This is is same as drawing this:
CH3
>C=O
CH3
But if u are asked to draw 'display' formula then u must show all bonds especially C=O, C=C and triple bond in CN as well as simple C-C and C-H bonds.

Thank you

 

[Someone2]

Does anyone have good notes for nanotechnology?? That topic is driving me crazy!!

 

[hellangel1]

cathode: Pb(s) -----> Pb2+(aq) + 2e–
anode: PbO2(s) + 4H+(aq) + 2e–---> Pb2+(aq) + 2H2O(l)

By considering the effect of decreasing [Pb2+(aq)] on the electrode potentials of
the cathode and the anode, deduce the effect of the overall Ecell.
State whether the Ecell will increase, decrease or remain the same.
Explain your answer.

Increasing the [pb2+ aq] causes equilibrium of 2nd reaction to shift backward and Electrode potential becomes less for the second reaction, and Electrode potential increases for the first reaction, ie Pb-->pb2+ + 2e-
So the E° for forward reaction is something less then +1.47 and for the backward reaction it is something more then -0.13
This causes the E cell to decrease