Chemistry: Post your doubts here!

[Rahma Abdelrahman]

Hahaha rightt my badd lol!
"oh simple things, where have you gone"

haha "I'm getting old and I need something to rely on"

 

[daredevil]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Can anyone solve Q:11,15,16,17,20

16: A
becz if all three of these elemts wen pput in that case do have lone electron pairs. but not all of them increase by 1. NO --> NO2 here N increases its ox state by 2.
20. D
just count all the double bonds (3) for pie bonds
then the single bonds. remember to count C-H bonds n -CH3 also bcz htat is a possible over look u might do. it will help if u mark with a pencil the bonds u have counted. also count one sigma bond for all the double bonds too bcz first a sigma bond is made and then a pie bond so they do have a sigma bond too. they are 25 in total.

don't know the others well enough to tell u sorry.

 

[Ahmedraza73]

16: A
becz if all three of these elemts wen pput in that case do have lone electron pairs. but not all of them increase by 1. NO --> NO2 here N increases its ox state by 2.
20. D
just count all the double bonds (3) for pie bonds
then the single bonds. remember to count C-H bonds n -CH3 also bcz htat is a possible over look u might do. it will help if u mark with a pencil the bonds u have counted. also count one sigma bond for all the double bonds too bcz first a sigma bond is made and then a pie bond so they do have a sigma bond too. they are 25 in total.

don't know the others well enough to tell u sorry.

not understand yet

 

[ahmed abdulla]

?:

 

[daredevil]

not understand yet

what didn't u understand? pin point the confusion so maybe then i can clear it out for u

 

[zackle09]

Make sure you use the correct units.
It doesn't necessarily have to be on the right or left side; it'll be on the side of the -CO2. For example, an ester will be like this: acid-CO2-alcohol, or alcohol-O2C-acid. The C of the CO2 will be part of the c. acid.

yeah so in part D isnt that the acid after CO2 instead of the alcohol :/

 

[h4rriet]

yeah so in part D isnt that the acid after CO2 instead of the alcohol :/

D is: CH2CH2CO2(CH2)4CH3. C is: CH3(CH2)4CO2CH2CH3 The underlined parts are from the carboxylic acids. D's is propanoic acid and C's is hexanoic acid. In the question, we start of with hexanol, with is then oxidised to hexanal, and then to hexanoic acid.

 

[zackle09]

D is: CH2CH2CO2(CH2)4CH3. C is: CH3(CH2)4CO2CH2CH3 The underlined parts are from the carboxylic acids. D's is propanoic acid and C's is hexanoic acid. In the question, we start of with hexanol, with is then oxidised to hexanal, and then to hexanoic acid.

so yeah they're saying that Y reacts with ethanol..and if Y is an hexanoic acid..shouldnt it have 6 Cs rather then 3

 

[h4rriet]

so yeah if the acid is hexanoic acid it should have 6 carbons..but in D it has only 3

That's why D is not the correct answer.

 

[zackle09]

That's why D is not the correct answer.

oh yeah! omg i was looking at the wrong question in the ms this whole time..sorrryy! lool
thanks alot for the help!

 

[Abu mota]

paper 1:
s08: Q.6,8,27,29,30,38
w08: Q.21,29,30,39

 

[Usman04]

hi guys im facing some problems in mcqs somebody plzz help
q 13, q 20, may june 09 p01
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf

 

[Mairaxo]

hi guys im facing some problems in mcqs somebody plzz help
q 13, q 20, may june 09 p01
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_1.pdf

Q13- all are soluble except CaCO3 so only it will precipitate
Q20 - its hard to explain in written form. just draw the structures and their isomers and you'll get 8.

 

[ahmed abdulla]

>?

 

[bravegirl123]

Could u e

there is no affect of the Cl-Cl bond or Br-Br bond here. The main bond here is H-Cl and H-Br. U should refer to there bonds to answer the question. Bond energies are diff according to the elements they are bonded to so we cant relate Cl-Cl and Br-Br to H-Cl and H-Br

could u please elaborate on that, i am still confused.

 

[cute97]

can someone help me with these this is my chem the question might be a piece of cake for any of u
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q 5, 6, 11, 33 the N=N bond point 2 can be right too, and 40
thanks in advance

 

[Abu mota]

paper 1:
s08: Q.6,8,27,29,30,38 http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
w08: Q.21,29,30,39 http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
plz help me, ty.

 

[syed1995]

can someone help me with these this is my chem the question might be a piece of cake for any of u
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q 5, 6, 11, 33 the N=N bond point 2 can be right too, and 40
thanks in advance

5 b .. whenever a state change occurs from liquid to gas.. the bonds are broken.. and hydrogen bonding is only present where H is joined with N, O or F.

6 A .. because of Hydrogen Bonding.. The IMF are high.. while to consider a gas to be an ideal gas the inter molecular forces need to be zero.

11 A .. because the Acid will react with OH- to decrease the concentration of OH- ions which will shift equilibrium to right hand side and more product forms...

33 D .. 2 Is wrong because Triple bond is in products and non-reversible reaction so that won't affect how the reactants react.. and N=N bond is present in N2H4 not triple bond.

40 B 1 is correct.. 2 is correct as 2 OH groups are present (OH) and -OH in COOH .. H bonded with O is hydrogen bonding, 3 is wrong since it will form a ketone from secondary alcohol.


I'd suggest that you revise the chapter on bonding from the book or ask your teacher to give you revision on the topic.. since your concepts on Hydrogen bonding seem to be a little weak

 

[syed1995]

>?

From the question's equation itself.

Replace R` with H.. since it's a Aldehyde.

R can be any alkyl group (CH3,C2H5)

So only possible answers are C and D.. as they are the only ones which contain the bonds Which I have shown in the above pic.

But D will be a product from a ketone as there are 2 R groups, 1 OH and 1 COO- Group attached to it! while we need only 1 R group for a aldehyde.. so answer is C.

 

[h4rriet]

paper 1:
s08: Q.6,8,27,29,30,38 http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
w08: Q.21,29,30,39 http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
plz help me, ty.

6. Use pV=nRT.
8. Volume is proportional to temperature at constant pressure. You can tell from pV=nRT.
27. Unreactive towards mild oxidising agents = tertiary alcohol. We can get only D from a tertiary alcohol.
29. B and C are not acidic; A is not chiral. That leaves D.
30. The acid used to make this ester is hexanoic acid. Only C shows a hexanoate.
38. Step 1 will give us the product so we won't need steps 2 and 3.

21. Any C=C bond breaks and is replaced with a C=O bond.
29. Draw propanone first, then break the double bond and add an H to the O and a -CN bond. The remove the CN and put CO2H in its place.
30. (30+30)-18(water).
39. Compounds 1 and 2 are formed by the reaction of C3H7 radicals. Compound 3 is formed by the reaction of a C4H9 radical with a C2H5 radical. These last can't be made if only propanone is used.