Chemistry: Post your doubts here!

[Asimadnan]

a member has answered this on one of the recent pages, you can see there

can u give me the link!!
i cant find it!!

 

[Casablanca]

a member has answered this on one of the recent pages, you can see there

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

 

[lavanyamane]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
Q.6 please?

 

[KurayamiKimmi]

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

exothermic-so should be decreased

 

[gary221]

1 cant be right cuz when you heat under reflux with alkali the -Cl is going to be replaced by -OH, on acidifying dehydration will occur so no way a carboxylic acid is produced. if one is wrong the answer is C

how come 3 is correct, then??

 

[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