Chemistry: Post your doubts here!

[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.

 

[gary221]

The ans in C.How come the denominator is (0.07*0.02) ? Please explain..
View attachment 7373

remember d formula, Kc = Molar conc of product/ molar conc of reactants (both raised to the power of thr stoichiometric coefficient)
Initial conc of H2 n I2 is 0.2 n 0.15 resp. Inititl conc of HI = 0
Final conc of HI = (0.26/2) as thr r 2 moles of HI formed
So. final conc of H2 = 0.20-0.13 =0.07
Final conc of I2 = 0.15 - 0.13 = 0.02

 

[gary221]

Hey can sum1 explain why the ans for this is c
View attachment 7369

hey does sum1 know how 2 solv this??

 

[hmlahori]

Can someone please give explanations to these paper 1 questions?​

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf​

Q3 What does 'ground state' mean? And r we supposed to write the '1s2 2s2....' electronic configuration to know the answer?​

Q21 Does an alcohol get oxidised by hot, concentrated manganate(7) ions?​

Q31 Why is the answer B not A? all the three statements seem correct.​

and Q38 Why cant the answer be B?​

​

 

[hm12]

hey does sum1 know how 2 solv this??

2 bond pairs 0 lone pairs 180 degree shape is linear
3 bond pairs 0 lone pairs 120 degree shape is trigonal planor
4 bond pairs 0 lone pairs 109.5 degree shape is tetrahedral
3 bond pairs 1 lone pairs 107 shape is trigonal pyramedal
2 bond pairs 2 lone pairs 104 bent shaped
5 bond pairs 0 lone pairs 90,120 degree shape is trigonal bipyramedal
6 bond pairs 0 lone pairs 90 degree shape is octahedral


Follow this and the answer will be C sulphur has two bond pairs two lone pairs so x would be 104 degree carbon has 4 b0nd pairs and 0 lone pairs so y is 109.5 degree nitrogen has 3 bond pairs and one lone pair so z is 107 degree so y>z>x so C is the answer