Chemistry: Post your doubts here!

[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 ..

 

[xhizors]

w11/13 http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf
Plz with little explanations
21, 35, 36, 37, 39, 40

and also
w11/12 http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q4(i tried twice plz with sol)
Q6, Q8
Q9(how, when temp in so pressure must be decreases to act like a ideal gas)
Q10(Hat is enthalphy change when one mole of gaseous atom is formed from its element under stp,,, plz briefly describe whats this is going on)

I would be really thankful, May Allah grant us the best success in our papers Ameen..

Plz any one PLZ pLZ PLz

 

[Jaf]

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.

If you read the question carefully enough, it states there's a cyclohexene ring and not a cyclohexane ring that the compound contains.
I guess there's no easier way to do this than to draw a quick small structure structure and count the number of hydrogen we're getting. :|

 

[gary221]

Hey can sum1 explain why the ans for this is c

 

[amatyasrizan]

Thankyou for the previous response Hm12 and histephenson007!Here goes another one..Why isnt the answer C?

 

[gary221]

Thankyou for the previous response Hm12 and histephenson007!Here goes another one..Why isnt the answer C?View attachment 7371

whts d ans for this?/

 

[amatyasrizan]

Why is the answer A?I don't see nitric acid being produced in A..please clear my doubts.Thankyou!

 

[amatyasrizan]

whts d ans for this?/

can you explain why C option doesnot work?

 

[gary221]

Why is the answer A?I don't see nitric acid being produced in A..please clear my doubts.Thankyou!
View attachment 7372

d ques is nt related 2 d formation of nitric acid,
u hv 2 calculate d oxidation no. of nitrogen in all d cases...
whr d greatesr chnge in nitrogen happens ie in A ( changes frm -3 to +2) is d correct ans..
hope i helped..

 

[amatyasrizan]

Look at those side chains (in the original molecule) carefully, the three of them are equal and have 3 alkene bonds each. ( Overall 9 alkene bonds). Look at the side chains we are to substitute it with : 2 side chains containing one alkene bond and 1 side chain with two alkene bonds. ( Overall 4 alkenes left).

Therefore in the process of the reaction, 9-4= 5 alkene bonds are broken. So, we need 5 molecules of H2.

Thankyou!

 

[amatyasrizan]

Tha

How to approach this question?Detailed method please..

in glyceryl trieleosterate the first chain has 31 hydrogen 2 chain has 30 hydrogen and 3 chain has 31 hydrogen making a total of 31+30+31=92 hydrogen

in soft margarine the first chain has 31 hydrogen and the two similar chains have 33+33=66 hydrogen making a total of 31+66=97 hydrogen so for converting one mole of glyceryl into soft margarine u need 97-92 =5 hydrogen so the answer is B

Thankyou! !

 

[gary221]

can you explain why C option doesnot work?

as far as i can see, increasing d temp, affects d energy.. not d no. of collisions, at least nt directly...i think d ans shud be D

 

[gary221]

Thankyou!

Tha

Thankyou! !

Thankyou for the previous response Hm12 and histephenson007!Here goes another one..Why isnt the answer C?View attachment 7371

@amatyasrizan, if sum1 helped u out...its btr 2 press the like button...

 

[amatyasrizan]

d ques is nt related 2 d formation of nitric acid,
u hv 2 calculate d oxidation no. of nitrogen in all d cases...
whr d greatesr chnge in nitrogen happens ie in A ( changes frm -3 to +2) is d correct ans..
hope i helped..

Oh!I i realize my mistake!TY!I'm bad with redox.Can you please explain me the balancing of ions in A?

 

[gary221]

Oh!I i realize my mistake!TY!I'm bad with redox.Can you please explain me the balancing of ions in A?

See, u only hv 2 luk at nitrogen on both sides...
on LHS, let d oxidation no of N be x, so x + 3(+1) = 0 {since thr r 3 hydrogen, n d overall chrge of the molecule is 0}
so, d oxidation no. of N is -3
On RHS, let d oxidation no of N be x, so x +(-2) = 0 {oidation no of oxygen is -2)
so. N= +2
thus, total change, +2-(-3) = +5

 

[amatyasrizan]

The ans in C.How come the denominator is (0.07*0.02) ? Please explain..

 

[Jaf]

in glyceryl trieleosterate the first chain has 31 hydrogen 2 chain has 30 hydrogen and 3 chain has 31 hydrogen making a total of 31+30+31=92 hydrogen

in soft margarine the first chain has 31 hydrogen and the two similar chains have 33+33=66 hydrogen making a total of 31+66=97 hydrogen so for converting one mole of glyceryl into soft margarine u need 97-92 =5 hydrogen so the answer is B

This is an incorrect way of explaining the question (and answer). This implies that hydrogen moles = hydrogen atoms which is NOT the case.

The way to go about this question is to see how many C=C (carbon - carbon double bonds) are hydrogenated. The original compound contained 9 C=C. The resultant margarine there has 4 C=C. This means 5 C=C were hydrogenated.
We also know that whenever a C=C bond is hydrogenated, 2 hydrogens are added to the carbons. For example, C2H4 becomes C2H6.
So 5 C=C bonds need 10 hydrogen atoms, and since one mole of hydrogen gives 2 hydrogen atoms (H2), 5 moles of H2 are needed.