Chemistry: Post your doubts here!

[Osake]

glad i could help ^^

I think you had a question revolving flameability of Halogenoalkanes? did yuo

 

[Osake]

I have a question Paper 1 winter 2008 Q39 , i dont get how to do it :
39 During the bromination of methane, the free radical •
3
CH is generated and a possible terminating
step of this reaction is the formation of C2H6 by the combination of two free radicals.
What could be produced in a terminating step during the bromination of propane?
1 CH3CH2CH2CHCH3
CH3
2 CH3CHCHCH3
CH3
CH3
3 CH3CH2CHCH2CH3
CH3
40 The structure of the antioxidant vitamin

 

[Casablanca]

help....anyone?

Could you check if the answer to 12 is C? If so, I could help. And if it's B, I still know how it works, but I think it's C.

(I thought since you helped me so much, I could try and help you out with this one. I tried doing 21, and I know how to do it usually, but my answer is wrong, so I don't think I'd be of much help with that one...)

 

[gary221]

help....anyone?

For 5, find the mass of Ni. It is 2 g.
We know 1 mole of any substance = 6.02 * 10^23 particles
thus, 1 mole of Ni = 58.7 g, which equals 6.02 * 10^23
so, 2 g = 2.05 * 10^22, ie A

 

[lavanyamane]

help....anyone?

Q5: no. of Ni atoms in 1 mol (58.7 g) = 6.02x10^23
hence, 20% of 10 = 2 g. In 2 g of Ni, no. of atoms = (2 x 6.02x10^23) / 58.7 = 2.05 x 10^22
Q10: i don't know!
Q12: H:O = 1:16
So, 16H = 1 Oxygen and the answer is C10H16O
Q21: The compound in the picture is part ester. It contains 6 C atoms. We already know ethanoic acid was use (2 C atoms). Now we need 4 C atoms more. Hence, the answer is C4... something. Acid + alcohol = ester. So X must me an alcohol. The alcohol with 4 C atoms is C4H9OH. But our ester already has a C=O, hence we cut out 2H and add another O to C4H9OH, giving C4H8O2

 

[KurayamiKimmi]

Assalamoalaikum wr wb!​

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need help, plz... ...​

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P.S. I'm reposting them ​

​

S has poor conducitivity when solid but conducts well in liquid state=must bean ionic compound
S has a mp of2800--this shows us that it has to MgO because in the course we are given the estimate mp of MgO (2000C)
T has a good conductivty in the solid state-so :
it cant be Sio2 or diamond -neither conduct electricity
options left =Cu or graphite -liquid conductivity is not known -Cu conducts in the liquid state too .so it has to be graphite

 

[KurayamiKimmi]

Could you check if the answer to 12 is C? If so, I could help. And if it's B, I still know how it works, but I think it's C.

(I thought since you helped me so much, I could try and help you out with this one. I tried doing 21, and I know how to do it usually, but my answer is wrong, so I don't think I'd be of much help with that one...)

thanks ^^ yes its C ..so how do you do it ?

 

[gary221]

help....anyone?

For 10, Kc = 4. Initial conc : ethanol = 1 mol Ethanoic acid = 1 mol Ethyl ethanoate = 0 mol Water = 0 mol
Final conc : Ethanol =(1-x)mol Ethanoic acid=(1-x)mol Ethyl ethanoate = x mol Water = x mol
Kc = 4 = [x] [x] /[1-x] [1-x]
4 = x^2/(1-x)^2
4- 8x+3x^2 = 0
Solve by quadratic eqn to gt d ans..
Hope i helped...

 

[KurayamiKimmi]

For 10, Kc = 4. Initial conc : ethanol = 1 mol Ethanoic acid = 1 mol Ethyl ethanoate = 0 mol Water = 0 mol
Final conc : Ethanol =(1-x)mol Ethanoic acid=(1-x)mol Ethyl ethanoate = x mol Water = x mol
Kc = 4 = [x] [x] /[1-x] [1-x]
4 = x^2/(1-x)^2
4- 8x+3x^2 = 0
Solve by quadratic eqn to gt d ans..
Hope i helped...

yes you did ^_^ thanks a lot

 

[Oliveme]

Please answer this question
Question 7 http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

Thank you so very much

 

[Aater Suleman]

THANKYOU!!!!!!!!!!!!!!!!!!!!!!!! SOOO MUCH!!!!!!!!

BS BS!!!!!!!parh bay k
LMAo

 

[Drift_king]

Is anybody is having any links related to chemistry MCQ'S revision.?????????

 

[sumaiyarox:)]

Is anybody is having any links related to chemistry MCQ'S revision.?????????

do past pprs...they help..

 

[jsg]

help needed in Q 9 and 3

 

[iKhaled]

guys i have found a mistake in the mark scheme of may june 11 paper 11 Oo

question 37, the answer is B? how come and an ammonium ion only has 8 electrons :S:S:S:S:S

 

[Leo Ahmed]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
Q 7...how to answer this question?
PLEASEEE HELP!!

 

[geek101]

guys i have found a mistake in the mark scheme of may june 11 paper 11 Oo

question 37, the answer is B? how come and an ammonium ion only has 8 electrons :S:S:S:S:S

option 1 says 10 which is true, 8 in the outer shell of bonded N and two in the inner shell, cuz N= 2, 5. so 1 is right

 

[iKhaled]

option 1 says 10 which is true, 8 in the outer shell of bonded N and two in the inner shell, cuz N= 2, 5. so 1 is right

this is the trickest question i have ever seen in my whole life ;o

 

[Paparazzi478]

11 0.144 g of an aluminium compound X react with an excess of water, to produce a gas. This gas
burns completely in O2 to form H2O and 72 cm3 of CO2 only. The volume of CO2 was measured at
room temperature and pressure.
What could be the formula of X?
[C = 12.0, Al = 27.0; 1 mole of any gas occupies 24 dm3 at room temperature and pressure]
A Al 2C3 B Al 3C4 C Al 4C3 D Al 5C3

Can anyone tell me how the answer is C
thankyou

 

[geek101]

this is the trickest question i have ever seen in my whole life ;o

but do you get why its 10