Chemistry: Post your doubts here!

[hmlahori]

please tell me how to do this question..i dont knw how many times i"ve posted it! but no one has answered it yet
its Q 22 of jun11/11 if you need to refer to the paper. answer is A. PLEASE HELP ME OUT!!

First of all we have to consider the outer electrons of both hydrogen and carbon. Normally CH3 has a total of (4 of carbon+3 of 3 H atoms) 7 outer electrons. For becoming a free radical CH3 does not need to add or remove electrons.(for example the chlorine free radical has the same number of outer electrons 7). So it will have 7 outer electrons. A nucleophile is a donator of a pair of electrons so the C in CH3 needs to gain one electron to have a free non bonding pair of electrons which it can donate(other electrons are already bonded with hydrogen). So it will have 8. An electrophile is an accepter of a pair of electrons so the C in CH3 needs to lose one electron so it can accept a pair of electrons and have a complete outer shell. So it will have 6.
Hope this helps.

 

[smartangel]

First of all we have to consider the outer electrons of both hydrogen and carbon. Normally CH3 has a total of (4 of carbon+3 of 3 H atoms) 7 outer electrons. For becoming a free radical CH3 does not need to add or remove electrons.(for example the chlorine free radical has the same number of outer electrons 7). So it will have 7 outer electrons. A nucleophile is a donator of a pair of electrons so the C in CH3 needs to gain one electron to have a free non bonding pair of electrons which it can donate(other electrons are already bonded with hydrogen). So it will have 8. An electrophile is an accepter of a pair of electrons so the C in CH3 needs to lose one electron so it can accept a pair of electrons and have a complete outer shell. So it will have 6.
Hope this helps.

thank you so much!! yes it did help me out

 

[smartangel]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q32.. please explain how 2 and 3 are correct!

 

[smartangel]

6 Which of the following least resembles an ideal gas?
A ammonia
B helium
C hydrogen
D trichloromethane
why is the ans A and not D when trichloromethane has a higher mass??

 

[user]

6 Which of the following least resembles an ideal gas?
A ammonia
B helium
C hydrogen
D trichloromethane
why is the ans A and not D when trichloromethane has a higher mass??

aoa wr wb!

Ammonia has hydrogen bonding......!! which is very strong as you know...
and for an ideal gas, one condition is that inter molecular forces are negligible..

 

[Afeef]

6 Which of the following least resembles an ideal gas?
A ammonia
B helium
C hydrogen
D trichloromethane
why is the ans A and not D when trichloromethane has a higher mass??

Gases like ammonia which has strong intermolecular attractions show more deviation ,
In D there exist weak van der wall forces i guess

 

[gestetner]

Help required in Q 1, 2, 40 of May/June 2005 P1
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s05_qp_1.pdf​

 

[Anoushay]

b

wel yes..u knw hw CIE is!!!

but it can be balanced by option A too.

 

[user]

Help required in Q 1, 2, 40 of May/June 2005 P1​

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s05_qp_1.pdf​

Q: 2

Assalamoalaikum wr wb!
Ok so they said, there's 1 mol of sodium azide..right?

from eqn 1, we know 2 moles produce 3 moles of nitrogen, so one mole will produce 3/2 moles of nitrogen and one mole of sodium...

now from eqn 2, we know 10 moles of sodium produce one mole of nitrogen, we got only one mole of sodium therefore how many nitrogen will be there..=> 1/10

total moles of nitrogen = 3/2 + 1/10 = 1.6

 

[smartangel]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q32.. please explain how 2 and 3 are correct!

 

[kshumaila52]

Can any one explain why option 3 is wrong ???? Q 38 June 06
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/

 

[smartangel]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
in 5 why cant the answer be D? i dont get what the examiner report is trying to say. please explain!!!

 

[gary221]

y dos the bond length increase btween hydrogen chloride,hydrogen bromide and hydrogen iodide?

Cl is more reactive as compared to Br... so it forms a stronger bond, n as a result, bond length is shorter.
Same applies to Br as compared to I.

 

[smartangel]

21 What is the total number of different chloroethanes, formula C2H6-nCln, where n can be any
integer from 1 to 4?
A 4 B 6 C 7 D 8
ans C. how?

 

[smartangel]

30 Which pair of compounds is formed when the ester C2H5CO2CH3 is boiled with aqueous sodium
hydroxide?
A C2H5CO2H CH3OH
B C2H5CO2Na CH3ONa
C C2H5CO2Na CH3OH
D C2H5OH CH3CO2Na
ans C. why cant it be A or B? please explain my questions. i really need help!

 

[leosco1995]

30 Which pair of compounds is formed when the ester C2H5CO2CH3 is boiled with aqueous sodium
hydroxide?
A C2H5CO2H CH3OH
B C2H5CO2Na CH3ONa
C C2H5CO2Na CH3OH
D C2H5OH CH3CO2Na
ans C. why cant it be A or B? please explain my questions. i really need help!

Split the ester by drawing a straight line through the middle of O2 and you will get these 2 compounds:

C2H5C & CH3

The carbon without the hydrogen (first one) will be the acid and the other one will be the alcohol. So your alcohol is CH3OH and the acid is C2H5CO2H. Since you boiled with aq. NaOH, the carboxylic acid becomes C2H5CO2Na.

 

[umarashraf]

30 Which pair of compounds is formed when the ester C2H5CO2CH3 is boiled with aqueous sodium
hydroxide?
A C2H5CO2H CH3OH
B C2H5CO2Na CH3ONa
C C2H5CO2Na CH3OH
D C2H5OH CH3CO2Na
ans C. why cant it be A or B? please explain my questions. i really need help!

mate first of all .. alcohols donot react with sodium hydroxide... secondly propanoic acid is an acid while sodium hydroxide is a base... this will readily react and form salt + h2O.... (acid base titration)

 

[smartangel]

mate first of all .. alcohols donot react with sodium hydroxide... secondly propanoic acid is an acid while sodium hydroxide is a base... this will readily react and form salt + h2O.... (acid base titration)

thanks..plz answer this on too
21 What is the total number of different chloroethanes, formula C2H6-nCln, where n can be any
integer from 1 to 4?
A 4 B 6 C 7 D 8
ans C. how?

 

[smartangel]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
in 5 why cant the answer be D? i dont get what the examiner report is trying to say. please explain!!!

 

[umarashraf]

thanks..plz answer this on too
21 What is the total number of different chloroethanes, formula C2H6-nCln, where n can be any
integer from 1 to 4?
A 4 B 6 C 7 D 8
ans C. how?

yes.. the answer is C but due to lack of skills i cant draw all the structures here..but can guide you just by sayin k if you use 1 cl, you can only have 1 orientation .. by using 2,3orb 4 carbons you can only make 2 2 and 2 orientations of the structure of chloroethane...