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Chemistry: Post your doubts here!

Aymen Ezazi

Aymen Ezazi

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strangerss said:
then why didn't they tell us to refer to the data booklet? the answer B is phosphorous? But how it's p orbital has 1 electron so it lost two electrons but they're asking for the electron configuration of it's second ionisation energy?
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yes it lost two electrons , but note that the second one is from an orbital closer to the nucleus , so has high 2nd ionisation energy, in C the 2nd ionisation energy will be little higher thn A bcoz its in p sub shell but 2 different orbitals, and A will have least 2nd ionisation energy bcoz its in s sub shell and both electrons in same orbital so will have greater repulsion.. i hope this made it clear :)
 
Aymen Ezazi

Aymen Ezazi

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strangerss said:
alsalam allaykom , http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf question 2 , I don't know what to understand from the graph, any help please?
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the third cross in this have the least ionisation energy that means it is from group one , and that would be sodium , and before sodium comes a noble gas , neon which will have the highest ionisation energy, and before neon is fluorine so that will be it :)
 
ahmed abdulla

ahmed abdulla

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Aymen Ezazi said:
the third cross in this have the least ionisation energy that means it is from group one , and that would be sodium , and before sodium comes a noble gas , neon which will have the highest ionisation energy, and before neon is fluorine so that will be it :)
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can u help with this :)
 

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Aymen Ezazi

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ahmed abdulla said:
can u help with this :)
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Q40 is easy, just look for an intermidiate, because there is always a curve downwards like this in the middle when ever they ask anything related to an intermediate, and in only 1 there is an intermediate formed when the Br is broken, THN the intrmediate forms thn OH group attaches.. in 2 and 3 no intermediate forms , there is only direct substituton..

the nxt question its not A bcoz alcohol reacts with H2SO4 to give an alkene, which is DEHYDRATION and not redox.. not C bcoz an ester is HYDROLYSED when heated with acid to give alcohol and carboxylic acid again no redox.. and its not D bcoz its a ketone and ketone DOES NOT REACT at all with Fehlings reagent and Tollen's reagent.. it is B bcoz the aldehyde gets OXIDISED to carboxylic acid and the Ag+ ions presnt in the solution gets REDUCED to Ag metal which forms a silver mirror in the test tube... i hope u got it :)
 
ahmed abdulla

ahmed abdulla

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Aymen Ezazi said:
Q40 is easy, just look for an intermidiate, because there is always a curve downwards like this in the middle when ever they ask anything related to an intermediate, and in only 1 there is an intermediate formed when the Br is broken, THN the intrmediate forms thn OH group attaches.. in 2 and 3 no intermediate forms , there is only direct substituton..

the nxt question its not A bcoz alcohol reacts with H2SO4 to give an alkene, which is DEHYDRATION and not redox.. not C bcoz an ester is HYDROLYSED when heated with acid to give alcohol and carboxylic acid again no redox.. and its not D bcoz its a ketone and ketone DOES NOT REACT at all with Fehlings reagent and Tollen's reagent.. it is B bcoz the aldehyde gets OXIDISED to carboxylic acid and the Ag+ ions presnt in the solution gets REDUCED to Ag metal which forms a silver mirror in the test tube... i hope u got it :)
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thanks ... if u look at ur textbook u will find that even 2 will form intermediate ie. SN2 ... so thats probably NOT the reason
 
h4rriet

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Abu mota said:
I'm sorry, but I still don't understand q.6, q.29 why is c not acidic(there is co2h bonded to it).
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No, that's a -CO2C-, not -CO2H. It's an ester bond.
For 6, all you gotta do is put the numbers they've given you into the formula. Also, one thing: V is found using mass/density.
 
daredevil

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Aymen Ezazi

Aymen Ezazi

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ahmed abdulla said:
whats the linkage between intermediate and the graph
i dont see the word intermediate in the question
how did u now the graph codes for intermediate rn
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yes they did not , but one of my friend who has already done A'levels and is in a uni now, expalined this.. that when and intermediate is formed the the energy decreases , one question like this came even in paper 2 with the same graph and had the intermediate mentioned..
 
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MONJUR HASAN NISHAD

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Okay chem dudes, I need some serious help! In my chem prac exam (p34) 2nd question my titration reading was 30.5 and our supervisor got 20.5! How much will I lose in that 2nd question??? In the first question, my point of intersection of that graph was 9.5 but the supervisor got 15. However I think two or three of my temperature readings were close to the supervisor. So how much will I lose in the first question??? Please help! I am having a heart attack here!
 
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MONJUR HASAN NISHAD

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One more query, how much overall marks do I need at AS to get 90th percentile? A is 80th percentile and you calculate the 90th percentile by this formula gt(for A) + gt(for A) - gt(for B)
 
AbbbbY

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unseen95

unseen95

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t
littlecloud11 said:
2) Ok, the word to emphasize on is RATE of reaction. Increasing the surface area of catalyst, increasing the temp and increasing the pressure all increases the RATE of reaction for the forward reaction but effects the YIELD of forward reaction differently. Increasing the catalyst SA means more molecules of the reactant can bind to the catalyst hence the rate increases, increasing temp means the reactant molecules have more energy, so the rate of successful collision increases and the rate increases (the yield of forward reaction would decrease because the forward reaction is exo. and the equilibrium will shift to the left), increase in pressure also increases the rate of forward reaction because there are greater no. of moles of reactant on the left. Only D, which involves removing the ammonia as it is formed does not effect the rate, but only effects the yield. So the answer is D.

14) the equation would be-
3 Ba(NO3)2 + 10 Al -------> 5Al2O3 + 3BaO + 3N2

Mr of Ba(NO3)2 = 137 + 14*2 + 16* 6 = 261
looking at the stoichiometry of the reaction, 3mols Ba(NO3)2 gives 3 mols N2. So-
3*261 g Ba(NO3)2 = 3*24 dm^3 N2
.783 g Ba(NO3)2 = .072 dm^3 N2 = 72 cm^3 N2
Your answer is B.

Gemeaux solved 24.
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thanks this answer helped me a lot :D
 
felicia tan

felicia tan

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37 Which compounds may result from mixing ethane and chlorine in the presence of sunlight?
1 CH3CH2Cl
2 CH3CH2CH2CH3
3 CH3CHCl CHCl CH3

Can anyone explain to me why is the answer A (1,2 and 3 is correct)
 
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