Chemistry: Post your doubts here!

[geek101]

When trying to increase the value of Kc for an exothermic reaction, should the temperature be increased or decreased? :/

Kc is products over reactants. to increase the value of Kc we need o increase the products. For a reaction where the forward reaction is endothermic (what you said) and increase in temp would favor the backward reaction, this will increase the reactants and lower Kc.....a decrease in temp would favor the forward reaction, so products will increase and so will Kc. Hence a decrease in temp is the answer to your question.

 

[lavanyamane]

N : P :K ratio
15:30:15
percentage nitrogen =(15/15+30+15) =0.25*100
25% of fertiliser;s mass is Nitrogen
reccommended usage is 14g
% of nitrogen in this =(25/100)*14
mass of nitrogen=3.5 g
no of moles =mass/Mr =3.5/14*2=0.125
concentration of N=0.125/5=0.025=0.03

Thank you so much! Life saver!

 

[Asimadnan]

Found it. I was right, the answer is C.

can u plz explain how is the answer C!!

 

[KurayamiKimmi]

Thank you so much! Life saver!

glad i could help ^^

 

[Zsiddiqui]

Found it. I was right, the answer is C.

how ?

 

[lavanyamane]

exothermic-so should be decreased

It should be decreased.

 

[Casablanca]

can u plz explain how is the answer C!!

"the answer is C since the moles of CO2 produced=atoms of CO2:
1mol=24dm3thus 24000cm3
mols that occupy 72cm3=72/24000
moles that occupy72cm3=3*10^-3
so carbon atoms=3*10^-3
mass of this carbon atoms= 3*10^3*12(mr)
mass=.036g
mass of almunium=mass of compund-mass of carbon atoms
mass of almunium=.144-.036=.108
moles of Al=mass/Mr
moles=.108/27=4*10^-3
mole ratio of Al:C ------>4*106-3:3*10^-3
thus simple ratio is 4:3
so compound is Al4C3"

Original answer by Muhammad Asif, credit goes to him, not me.

 

[geek101]

how come 3 is correct, then??

alkaline hydrolysis of nitrites produces sodium salts, which on further acidifying will give you a carboxylic acid.

 

[KurayamiKimmi]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

Can anyone Please solve questions 5-10-12-21? pretty please ^^

help....anyone?

 

[Casablanca]

Thank you all so much for your help, I have my chemistry MCQs in about 8 hours so I'm going to head off to bed now. Best of luck to all of you, and I hope you get the best grades possible.

Remember to wish me luck in your hearts as well, as you all know, I'm going to need all the luck I can get. >_<

 

[user]

glad i could help ^^

Can you help me with my questions?

 

[KurayamiKimmi]

Thank you all so much for your help, I have my chemistry MCQs in about 8 hours so I'm going to head off to bed now. Best of luck to all of you, and I hope you get the best grades possible.

Remember to wish me luck in your hearts as well, as you all know, I'm going to need all the luck I can get. >_<

zone 4 ?=D

 

[KurayamiKimmi]

Can you help me with my questions?

i'll try ^^

 

[Asimadnan]

"the answer is C since the moles of CO2 produced=atoms of CO2:
1mol=24dm3thus 24000cm3
mols that occupy 72cm3=72/24000
moles that occupy72cm3=3*10^-3
so carbon atoms=3*10^-3
mass of this carbon atoms= 3*10^3*12(mr)
mass=.036g
mass of almunium=mass of compund-mass of carbon atoms
mass of almunium=.144-.036=.108
moles of Al=mass/Mr
moles=.108/27=4*10^-3
mole ratio of Al:C ------>4*106-3:3*10^-3
thus simple ratio is 4:3
so compound is Al4C3"

Original answer by Muhammad Asif, credit goes to him, not me.

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

 

[user]

Assalamoalaikum wr wb!

need help, plz... ...

P.S. I'm reposting them

 

[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