Chemistry MCQ thread...

[ninjas4life]

why cant it be c?

 

[xHazeMx]

EXPLANATION ?

why this is not B ?????? any one can explain it ??

Because the number of moles at equilibrium is 1.1, not 1.0.
For Kp expressions you need the partial pressures of everything at equilibrium.
To figure out the partial pressure of something you need these equations:

partial pressure = mole fraction X total pressure
mole fraction = number of moles of a particular gas / total number of moles of gas

Now, back to the question:
We'll just assume that we start off with 1 mole of steam.
20% of it is converted to oxygen and hydrogen.
So now, at equilibrium, we have 0.80 mol of steam, 0.20 mol of hydrogen and 0.10 mol of oxygen (only 1 mole of oxygen compared to 2 moles of hydrogen and steam). In total, we have 1.10 moles of gas.
To find out the mole fractions we use the above equation, I'll just do the partial pressure of steam to make it clear for you :
mole fraction of steam = 0.80/1.10
and partial pressure of steam = mole fraction X total pressure = (0.80/1.10) X 1.0

I'm not very good at explaining and everything's a bit muddled but I hope you understood some of it.

i m just confused about B the total moles is also 1 .. 0.067, 0.133 and 0.80 would also give the partial pressure

 

[Zishi]

D. because esters hydrolyse to give alcohols and acids.

 

[xHazeMx]

how the total initial moles will be 1 and at equilibrium after dissociation its 1.1 ??????

 

[Zishi]

how the total initial moles will be 1 and at equilibrium after dissociation its 1.1 ??????

We're presuming that moles of steam will be 1, and that of H2 and O2 would be 0. According to balanced equation, 0.2 moles of steam will form 0.2 moles of H2 and 0.1 moles of O2. After this steam will remain with 0.8 moles. So total number of moles after equilibrium is set up = 0.8+0.2+0.1 = 1.1

 

[xHazeMx]

how the total initial moles will be 1 and at equilibrium after dissociation its 1.1 ??????

We're presuming that moles of steam will be 1, and that of H2 and O2 would be 0. According to balanced equation, 0.2 moles of steam will form 0.2 moles of H2 and 0.1 moles of O2. After this steam will remain with 0.8 moles. So total number of moles after equilibrium is set up = 0.8+0.2+0.1 = 1.1

also 0.20 can be distributed as 0.067, 0.133 and 0.80 obtaining the same ratio so the total number will be 1 right ? :%) :%)

 

[Zishi]

how the total initial moles will be 1 and at equilibrium after dissociation its 1.1 ??????

We're presuming that moles of steam will be 1, and that of H2 and O2 would be 0. According to balanced equation, 0.2 moles of steam will form 0.2 moles of H2 and 0.1 moles of O2. After this steam will remain with 0.8 moles. So total number of moles after equilibrium is set up = 0.8+0.2+0.1 = 1.1

also 0.20 can be distributed as 0.067, 0.133 and 0.80 obtaining the same ratio so the total number will be 1 right ? :%) :%)

No. You're thinking wrong. Ok tell me how many moles of H2 and O2 will be formed from 1 mole of H2O?

 

[xHazeMx]

No. You're thinking wrong. Ok tell me how many moles of H2 and O2 will be formed from 1 mole of H2O?

1 mole of hydrogen and half mole of oxygen

 

[Zishi]

No. You're thinking wrong. Ok tell me how many moles of H2 and O2 will be formed from 1 mole of H2O?

1 mole of hydrogen and half mole of oxygen

LOL! You answered your own question. So as 0.2 moles of steam decompose, so 0.2 moles of H2 and 0.1 moles of O2 will form. :roll:

 

[xHazeMx]

No. You're thinking wrong. Ok tell me how many moles of H2 and O2 will be formed from 1 mole of H2O?

1 mole of hydrogen and half mole of oxygen

LOL! You answered your own question. So as 0.2 moles of steam decompose, so 0.2 moles of H2 and 0.1 moles of O2 will form. :roll:

LOL!! sorry studied too much today !

 

[MHHaider707]

if we compare Mg2+ and Ba2+ ions then which ion is more polarizing???

 

[intel1993]

Mg2+ is more polarizing coz as we go down the grup atomic radiii increases due to which charge density decreases hence polarizing power decreases so Ba2= less polarizing........

 

[xHazeMx]

if we compare Mg2+ and Ba2+ ions then which ion is more polarizing???

Mg2+ because it has higher second ionisation energy
correct me if i m wrong

 

[xHazeMx]

Mg2+ is more polarizing coz as we go down the grup atomic radiii increases due to which charge density decreases hence polarizing power decreases so Ba2= less polarizing........

thats correct

 

[xHazeMx]

1 and 2 are correct but how 3 is possible ???

 

[Zishi]

1 and 2 are correct but how 3 is possible ???

I reckon it's because CH3CHCl* free radicals may combine to form CH3CHClCHClCH3

 

[Mssamgirl15]

http://www.xtremepapers.me/CIE/Internat ... 8_qp_1.pdf

Guys, May/June 2008 question number 6 or click on the link above.
Please answer this question. I can't upload a screenshot for some reason. :/

 

[MHHaider707]

20 When gaseous chemicals are transported by road or by rail they are classified as follows.
flammable non-flammable poisonous
Which commonly transported gas is non-flammable?
A butane
B hydrogen
C oxygen
D propene

Why is oxygen non-flammable?

 

[maybeitwasnoone]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s08_qp_1.pdf

Guys, May/June 2008 question number 6 or click on the link above.
Please answer this question. I can't upload a screenshot for some reason. :/

You used PV=nRT?

 

[Zishi]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s08_qp_1.pdf

Guys, May/June 2008 question number 6 or click on the link above.
Please answer this question. I can't upload a screenshot for some reason. :/

pV=nRT

20 When gaseous chemicals are transported by road or by rail they are classified as follows.
flammable non-flammable poisonous
Which commonly transported gas is non-flammable?
A butane
B hydrogen
C oxygen
D propene

Why is oxygen non-flammable?

Being flammable means burning in oxygen. Obviously you can't burn oxygen IN oxygen.