Chemistry: Post your doubts here!

[ahmed abdulla]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
q 8 and 28 plz ?

 

[iKhaled]

for question 8 u need to do a hess cycle diagram which will look like this....

the values of 590 and 1150 are the first and second ionisation energies!

for question 28 the answer is B because if u can see when we write skeletal formulas we dont include the hydrogen attached on the carbon. the only one that has that is B!

 

[knowitall10]

Who's still discussing chemistry iKhaled ?

 

[iKhaled]

Who's still discussing chemistry iKhaled ?

i still have paper one on the way!

 

[Fatum Zuh]

Help me pls!
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_3.pdf
Question 3[ii], [c] and [d][ii][iii]
Thanks

 

[iKhaled]

Help me pls!
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_3.pdf
Question 3[ii], [c] and [d][ii][iii]
Thanks

lol??? IGCSE paper in this thread go to the IGCSE forums dude

 

[strangerss]

HEY can some one please check if the answer in the marking scheme in paper May/June 2011 33 for question c is correct , from where they brought the 10 to multiply? can some one pleasee help?

 

[hela]

where can I find old past papers MCQ PAPER 1

 

[hela]

how to get old past papers for chemistry AS AND A LEVEL

 

[Warrior66]

HEY can some one please check if the answer in the marking scheme in paper May/June 2011 33 for question c is correct , from where they brought the 10 to multiply? can some one pleasee help?

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_33.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_ms_33.pdf
I guess you're talking about 1 c part iii, you have to multiply the answer you got in part ii with 10 because if 25 cm3 of Fa1 have the amount of moles you found out for ii, then 250 cm3 of FA1 has 10 times as much amount of moles..
see, i think you're confused because you probably think that the II mark on the mark scheme is for part ii. But it's not. It is one whole mark consisting of what calculation you did in part ii and iii.
Then for iv you multiply the Mr of FA1 with the moles from iii and then divide it by the mass of FA1 you found in 1a. 'weighing out the salt' part and times it with 100.

 

[Umar Zain]

For question 1. (e)(ii) [36/ON/2010]... i don't understand why "Puts acid/FB 3 in burette and pipettes NaOH/ FB 2
into flask" can overcome the problem

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
Question 10
How do I know the bond angles in these options and how to find the answer!? I'm clueless.

Angles between 109 and 110 are for tetrahedral molecules with 4 bonds. SiO2 has a tetrahedral structure, that's known; so does propane. If you draw the structure of ethanoic acid, you'll see that one C is attached to 4 other groups, therefore the bond angle for it must be 109.5. That leaves graphite.

 

[h4rriet]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
q 8 and 28 plz ?

8. You must draw a Hess cycle for this:

590 is the first ionisation energy, and 1150 is the second.
28. You first draw the structural formula of the monomer, then the skeletal:

 

[Islam Atef]

guys please I need june and november 2002 markscheme for paper 1

 

[Rahma Abdelrahman]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_11.pdf
Please ... for Q22, why the answer is B? Ok I know that for CH3 to be an electrophile it should have less than 8 electrons, so answer is not D, And for nucleophile it shd have lone pair of electrons.. but how do we apply this here?
And also Q34, Q36,

 

[mrnt3250]

guys please I need june and november 2002 markscheme for paper 1

U don't post it here.
It's in Examiner's Report, and please Google it. ( hint: 9701_S02_er.pdf)
http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2002jun/9701_s02_er.pdf

 

[Es Jay]

for enthalpy change of atomisation/ dissociation, do the elements initially have to be in there gaseous states?

 

[mrnt3250]

for enthalpy change of atomisation/ dissociation, do the elements initially have to be in there gaseous states?

Atomization converts the element in any state to its gaseous state.

 

[Es Jay]

Atomization converts the element in any state to its gaseous state.

thank you xD

 

[darknessinme]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_11.pdf
Please ... for Q22, why the answer is B? Ok I know that for CH3 to be an electrophile it should have less than 8 electrons, so answer is not D, And for nucleophile it shd have lone pair of electrons.. but how do we apply this here?
And also Q34, Q36,

22. Draw the structure of CH3:
Nucleophile has a lone pair it can donate. So outer shell has 8e-, 6e- for bonding and 1 lone pair.
Electrophile can accept a pair of electrons. 6e- in outer shell needed to bond, and so it has an incomplete octet. Outer shell can accept a lone pair.
Free Radical has an unpaired electron, so 6 used for bonding and one lone e- by itself, so 7e- in total.
Answer is A.

34.
1. True, Learn it.
2. True, Learn it.
3. False. General knowledge that table salt in water is neutral.
Answer B

36.
1. True,Bond energy of Hal-Hal decreases down group, because bond length increases. So Astatine molecules should dissociate more easily than chlorine.
2. False, Reactions between halogen and hydrogen get less vigorous down group 7. Becomes an equilibria with I2, so conclude that it reacts slowly with Astatine.
3. False, Halogens get weaker as oxidising agents down the group.
Answer D