Chemistry: Post your doubts here!

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
9,10,35 And 39

AoA,
Q9:
pressure is directly proportional to number of moles of solute, as from the equation moles of solute are increasing pressure increases
, and it is obvious that glucose and fructose are not optical isomers so they are structural isomers
Therefore, the answer is D

Q10:

Thus, A is the answer!

Q35:
When firework is lit, heat is given to barium nitrate and it decomposes due to heat
Ba(NO3)2 --> BaO + 2NO2 + 0.5O2
BaO can be reduced to barium by Mg, and in doing so MgO will form
However, since the nitrate is not stable to heat, magnesium nitrate cannot form!
That means options 1 and 2 are correct and 3 is wrong
That is why B is the answer!

Q39:
You should know from the knowledge of reactions why options 2 and 3 are correct!
1 is incorrect because by boiling CH3CH2Cl under reflux with dilute alkali will produce CH3CH2OH
but adding mineral acid will not turn it into ethanoic acid, that can only be done by oxidation under reflux!

 

[smzimran]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s10_qp_42.pdf
q3 c (i) carbon aslo has an empty 2p orbital so why it cant react

AoA,
Because carbon, in excited state has a filled p-orbital and new electrons are repelled
If there was an extra empty orbital available, it would make bonds!

 

[hassam]

hmm that seems to be a reasonable explanation...thanks

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_4.pdf
in Q2 part e.. isnt the ratio of electrons to hydrogen 2:1.. hence when we get mol of electron by 345600/96500 we divide it by 2 to get get mol of hydrogen wich will also be its mass? PLEASE ANSWER

AoA,
the half equation is:
H2(g) --> 2H+(aq) + 2e
Q = It = 0.01 * 400 * 24 * 3600 = 3.45 * 10^5 C
mol of electrons = Q / Faraday constant
= (3.45 * 10^5) / (9.65 * 10^4)
= 3.6 mol
2 mol electrons produce 2g hydrogen gas (1 mol)
3.6 mol will produce
= (2 / 2) * 3.6
= 3.6 g

 

[hassam]

well @smz imran when 4 cl will be bonded to carbon......its p orbital will be filled as opposed to when 3Cl will be bonded toB....its p orbital will still have space to accomodate a lone pair of electrons
i dint thought abt the bonded situation and got confused

 

[smzimran]

well @smz imran when 4 cl will be bonded to carbon......its p orbital will be filled as opposed to when 3Cl will be bonded toB....its p orbital will still have space to accomodate a lone pair of electrons
i dint thought abt the bonded situation and got confused

So, is there still confusion ?

 

[hassam]

no now its okay..........well this hydrolysis occur via SN2 SIMILAR mechanism ryt....that why we need empty orbitals for transition state to form???

 

[Ahmed Ali Akbar]

oct/nov 09 mcq 40..Paper12..explanation is required....Please....with explanations..!!!!

 

[smartangel]

in Q5 part b..why does the marking scheme give positive E values? im getting negative..
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_43.pdf

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s08_qp_4.pdf
Q2 a iii.. how do we balance the equation using oxidation numbers?

 

[JD REBORN]

AoA,
Q9:
pressure is directly proportional to number of moles of solute, as from the equation moles of solute are increasing pressure increases
, and it is obvious that glucose and fructose are not optical isomers so they are structural isomers
Therefore, the answer is D

Q10:
View attachment 7325
Thus, A is the answer!

Q35:
When firework is lit, heat is given to barium nitrate and it decomposes due to heat
Ba(NO3)2 --> BaO + 2NO2 + 0.5O2
BaO can be reduced to barium by Mg, and in doing so MgO will form
However, since the nitrate is not stable to heat, magnesium nitrate cannot form!
That means options 1 and 2 are correct and 3 is wrong
That is why B is the answer!

Q39:
You should know from the knowledge of reactions why options 2 and 3 are correct!
1 is incorrect because by boiling CH3CH2Cl under reflux with dilute alkali will produce CH3CH2OH
but adding mineral acid will not turn it into ethanoic acid, that can only be done by oxidation under reflux!

For Q39 i dont understand what will happen when aqueous akali is added to compund 2(ester) and compound 3(nitrile)?

 

[smzimran]

For Q39 i dont understand what will happen when aqueous akali is added to compund 2(ester) and compound 3(nitrile)?

hydrolysis for ester and nothing to mitrile
nitrile will be converted when acidified!

 

[DPratik]

plz can anyone help me in solving question no 5)b)4

 

[DPratik]

Hi guys
Can anyone tell me something about complex ions? One past paper question asked me to draw the displayed shape of d-orbitals of metal cation in complex ions, and to explain the energy differences among the d-orbitals. I felt like my teacher did not mention this part.

The d-orbital is divided into two energy levels,two of the orbitals stay in higher energy level and three of the orbitals stay in lower energy level and the amount of energy absorbed by the complex ion is exactly equal to the difference in the energy between those levels..


if you look at the picture the two orbitals at the bottom are at higher energy level and the top three orbitals are at lower energy level and the reason why the two orbitals are at higher energy is because they lie close to the ligands !!!

 

[iKhaled]

hello guys!

can a chemist please help me..

i need explanation for some of the questions in paper 1 oct/nov 05

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

Q3, Q5, Q14, Q16, Q17, Q18, Q29, Q30, Q38.​

please helppp... :/​

 

[DPratik]

hello guys!​

​

can a chemist please help me..​

​

i need explanation for some of the questions in paper 1 oct/nov 05​

​

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf​

​

Q3, Q5, Q14, Q16, Q17, Q18, Q29, Q30, Q38.​

please helppp... :/​

for question 5,the answer is HCl,though we don't have to know much in detail about it but just keep in mind that the heavier the mass more it will be deviated from ideal gas.
for question 14,just draw the orbital in box form,you can see that phosphorus has half filled p-orbital which means it has the highest ionization energy and as silicon no doubt has the has highest melting point and as sulphur exist in S8 form which means it has higher melting point than phosphorus which exist in P4 form
for question 18,if you form a equation the you can see that ammonia,calcium sulphate and water is formed,so obviously the answer is C
for question 29,there is no presence of aldehyde so no effect of Fehlings reagent,as it can't declourise bromine becuase there is no double bond present in carbon chain so that bromine can be declourises,it is soluble in water so lastly we have just one option left but if you still wana now how the option is D then search about acid anhydride,it might help you
for question 30,you can see that the chain seems like ester chain,so obviously the answer is hydrolysis

 

[Jaf]

Question 20 here PLEASE! :
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf

 

[DragonCub]

Question 20 here PLEASE! :
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf

Deduct the aldehyde group and cyclohexane group, which are CHO and C6H11 respectively. What remains are 13 carbons and 16 hydrogens, and these are involved in the aliphatic chain.
Suppose a saturated (no double bonds) aliphatic chain with 13 carbons. The corresponding hydrogen number should be 26 (two terminals are not hydrogen atoms). Each time altering one C-C to C=C will lose 2 hydrogen atoms. So there are (26-16)/2 = 5 C=C double bonds.
CIS means the hydrogen atoms are on the same side. So the answer is A.

 

[iKhaled]

for question 5,the answer is HCl,though we don't have to know much in detail about it but just keep in mind that the heavier the mass more it will be deviated from ideal gas.
for question 14,just draw the orbital in box form,you can see that phosphorus has half filled p-orbital which means it has the highest ionization energy and as silicon no doubt has the has highest melting point and as sulphur exist in S8 form which means it has higher melting point than phosphorus which exist in P4 form
for question 18,if you form a equation the you can see that ammonia,calcium sulphate and water is formed,so obviously the answer is C
for question 29,there is no presence of aldehyde so no effect of Fehlings reagent,as it can't declourise bromine becuase there is no double bond present in carbon chain so that bromine can be declourises,it is soluble in water so lastly we have just one option left but if you still wana now how the option is D then search about acid anhydride,it might help you
for question 30,you can see that the chain seems like ester chain,so obviously the answer is hydrolysis

thank you sooooooooooooo much bro..

dude do u have any good chemistry note ( organic notes)..if you do please tell me about them and thank u again!

 

[Amy Bloom]

Can anybody reply to my question please??

 

[xhizors]

i am really confused what is the difference btw nucleophili addition and nucleophilic substution? can someone explain it to me properly?

(talking with alkene repectives)nuclophilic addition ocurs when double bond is broken and partial negative element is added and nuclophilic substitution occurs by replacing H or other elemnts ..