Chemistry: Post your doubts here!

[Ahmed Khider]

guys when will May june 2012 past papers will be out? please upload here yaar..

Here>>>

Olevel.sourceforge.net​

 

[Amy Bloom]

which atom has three unpaired electron ??
A) Al
B) Se
C) Cr
D) Co
plz do explain .....

Didn't get the answer, are u sure the question is well asked? well, i wrote the electronic configurations as shown in the attached file. Try to think in this way and see what u get.

 

[Amy Bloom]

Hello there! Here are my doubts:
1) How can an ideal gas obey boyle's laws of gases, that of pressure is inversely proportional to volume?
2) Using, PV = nRT, sketch a graph of P against V (with some mathematical explanations)
3) Sketch a graph to show the pressure of a constant mass of an ideal gas will vary as temperature rises from absolute zero in a container of constant volume. How will the graph change if the gas tends to dissociate as the temperature increases. example: N2O4(g) -----> 2NO2(g) [this reaction is feasible only on the action of heat on N2O4(g)]

 

[alphabravocharlie]

Hello there! Here are my doubts:
1) How can an ideal gas obey boyle's laws of gases, that of pressure is inversely proportional to volume?
2) Using, PV = nRT, sketch a graph of P against V (with some mathematical explanations)
3) Sketch a graph to show the pressure of a constant mass of an ideal gas will vary as temperature rises from absolute zero in a container of constant volume. How will the graph change if the gas tends to dissociate as the temperature increases. example: N2O4(g) -----> 2NO2(g) [this reaction is feasible only on the action of heat on N2O4(g)]

well the second one: p = [nRT]/V. nRT can be considered constant so graph would be an inverse relation graph
as for the other 2, hmh, smzimran zara madad kejiay ga

 

[Amy Bloom]

Hey i have some challenging questions for u. These have been really annoying mCQs for me.
I've attached them in this file. answers in red.
I would be grateful if u could provide me with supporting short explanations.
Tnx.

 

[Amy Bloom]

well the second one: p = [nRT]/V. nRT can be considered constant so graph would be an inverse relation graph
as for the other 2, hmh, smzimran zara madad kejiay ga

U mean this? (consider B, only the SHAPE, i just quickly googled a pic to confirm.)

 

[smzimran]

Hello there! Here are my doubts:
1) How can an ideal gas obey boyle's laws of gases, that of pressure is inversely proportional to volume?
2) Using, PV = nRT, sketch a graph of P against V (with some mathematical explanations)
3) Sketch a graph to show the pressure of a constant mass of an ideal gas will vary as temperature rises from absolute zero in a container of constant volume. How will the graph change if the gas tends to dissociate as the temperature increases. example: N2O4(g) -----> 2NO2(g) [this reaction is feasible only on the action of heat on N2O4(g)]

1. Ideal gas already obeys boyle's law, charles law, gay lussac's law and avagadro law!!!

2. alphabravocharlie is correct!

U mean this? (consider B, only the SHAPE, i just quickly googled a pic to confirm.)

^ B is correct!
and for the mathematical proof part, as P is inversely proportional to V, Temperature and number of moles are constant and gradient of the straight line obtained in graph of P against 1/V is equal to nRT

 

[alphabravocharlie]

1. Ideal gas already obeys boyle's law, charles law, gay lussac's law and avagadro law!!!

2. alphabravocharlie is correct!


^ B is correct!
and for the mathematical proof part, as P is inversely proportional to V, Temperature and number of moles are constant and gradient of the straight line obtained in graph of P against 1/V is equal to nRT

Jazakallah mate

 

[Amy Bloom]

1. Ideal gas already obeys boyle's law, charles law, gay lussac's law and avagadro law!!!

2. alphabravocharlie is correct!


^ B is correct!
and for the mathematical proof part, as P is inversely proportional to V, Temperature and number of moles are constant and gradient of the straight line obtained in graph of P against 1/V is equal to nRT

THANKS smzimran & alphabravocharlie, I'll pray for all of u guys who helped me, in one way in the other, for u to achieve good grades.
Can u help me with the document (questions states of matter.doc) i recently posted?

 

[yumichikabyakuya renji]

please can anyone explain to me how the answer is D for this question from jun 2o10 Q10?
and explain how i can upload a question on this site,,, i am new to it,, plz...

 

[Amy Bloom]

please can anyone explain to me how the answer is D for this question from jun 2o10 Q10?
and explain how i can upload a question on this site,,, i am new to it,, plz...

To upload a paper i usually save it and upload it. Or i think u can paste the link from the address bar on top of ur web browser, which is quicker.

First u need to consider the amount of H+ dissociated for a pH of 6 and 9. Which is approximately 0.1 and 0.2 respectively. use the pH = -log10[H+] relationship.
If for pH = 6
2 moles of X dissociate to give 0.1 mole of H+
1 mole of X dissociate to give approx. 0.5 mole of H+ ( which is not the kind of behaviour of a a strong acid, so student P is wrong, eliminating answers A and C)

For pH=9
2 moles of Y dissociate to give 0.2 mole of H+
1 mole of Y dissociate to give 0.1 mole of H+ (which is the kind of behaviour of either a weak acid or a weak base where partial dissociation occurs. Hence student Q was definitely correct, eliminating answer B)
So the answer is D.

 

[Bikalpa kattel]

hey anyone please provide me A level may june 2012 past papers..

 

[alphabravocharlie]

Hey i have some challenging questions for u. These have been really annoying mCQs for me.
I've attached them in this file. answers in red.
I would be grateful if u could provide me with supporting short explanations.
Tnx.

Q3: PV = nRT, where n = mass/mr
so mr = [mass * R * T]/P*V so ans is D

Q4: same as q 3

 

[Amy Bloom]

Q3: PV = nRT, where n = mass/mr
so mr = [mass * R * T]/P*V so ans is D

Q4: same as q 3

Yeah, i know about that , can u try to explain? i mean, are there conversions involved etc? can u explain the HOW of the answers?

 

[alphabravocharlie]

Yeah, i know about that , can u try to explain? i mean, are there conversions involved etc? can u explain the HOW of the answers?

Well in q3 all you have to do is substitute the values to get the answers. the only conversion is the cm3 to dm3 conversion.
in q4, i don't really get it, but option a is the only correct one, all others wrong, C and D are wrong because T should be in numerator. B is wrong because the temperature given is already given in K so no need to add 273. leaving option A.

 

[yumichikabyakuya renji]

To upload a paper i usually save it and upload it. Or i think u can paste the link from the address bar on top of ur web browser, which is quicker.

First u need to consider the amount of H+ dissociated for a pH of 6 and 9. Which is approximately 0.1 and 0.2 respectively. use the pH = -log10[H+] relationship.
If for pH = 6
2 moles of X dissociate to give 0.1 mole of H+
1 mole of X dissociate to give approx. 0.5 mole of H+ ( which is not the kind of behaviour of a a strong acid, so student P is wrong, eliminating answers A and C)

For pH=9
2 moles of Y dissociate to give 0.2 mole of H+
1 mole of Y dissociate to give 0.1 mole of H+ (which is the kind of behaviour of either a weak acid or a weak base where partial dissociation occurs. Hence student Q was definitely correct, eliminating answer B)
So the answer is D.

hey thXx very much

 

[yumichikabyakuya renji]

Hey i have some challenging questions for u. These have been really annoying mCQs for me.
I've attached them in this file. answers in red.
I would be grateful if u could provide me with supporting short explanations.
Tnx.

Q1) (let the temperature be T, as it is unknown and will cancel afterwards)

in small spacecraft
number of moles = PV/RT = (6.02x10^4)/T
in larger spacecraft
no. of moles = (3.61x10^5)/T

total no. of moles= (6.02x10^4)/T + (3.61x10^5)/T
= (4.21x10^5)/T
total volume = 10+30 = 40 m^3

then you calculate pressure using
PV=nRT
P= nRT/V
=( [(4.21x10^5)/T] x 8.31 x T)/40......... T cancels out, s0rry if i confuse u with lots of brackets
= 87.5 kPa


Q2) u hav to calculate the number of moles of steam= 1/18
= .0556
then we say,
1 mol of steam occupies 24 dm^3 at 298 K
.0556 mol of steam will occupy (24*.0556)=1.333 dm^3 at 298 K

At 298 K, steam occupies 1.333 dm^3
At 596 K, it will occupy [(1.333/298)*596]= 2.67 dm^3



Q3) P= 1.0x10^5 V= 83.1 cm^3 T= (27 + 273) = 300 K
we know that no. of moles= mass/Mr,
hence,
PV=nRT
1.0x10^5 x 83.1x10^-6 = (0.10/Mr) x 8.31 x 300

then u cross-multiply, and u get the expression in D.


Well, for Q4 i didn't get the answer, but for Q5 u r right, it's C since gases behave ideally at low pressure and high temperature.

 

[Amy Bloom]

yumichikabyakuya renji : Thanks a lot. Your explanations indeed really helped.
For question 4 i got some light, let me share it with you: When using the formula PV=nRT, T should be at the numerator, eliminating answers C and D. However, the temperature given in the question is already in kelvins, so you don't need to add 273 to the temperature, so, you eliminate answer B leaving only A correct.

 

[yumichikabyakuya renji]

yumichikabyakuya renji : Thanks a lot. Your explanations indeed really helped.
For question 4 i got some light, let me share it with you: When using the formula PV=nRT, T should be at the numerator, eliminating answers C and D. However, the temperature given in the question is already in kelvins, so you don't need to add 273 to the temperature, so, you eliminate answer B leaving only A correct.

for that ok but i didn't understand the "22400" part, i know its about 24dm^3 but could u explain to me in more details? thXx
Well, i followed ur instructions about copying URL and uploading stuff and yay! i succeeded, thXx once again
i recently posted 2 of my doubts, if u cud help,,,

 

[Amy Bloom]

for that ok but i didn't understand the "22400" part, i know its about 24dm^3 but could u explain to me in more details? thXx
Well, i followed ur instructions about copying URL and uploading stuff and yay! i succeeded, thXx once again
i recently posted 2 of my doubts, if u cud help,,,

Me too, i don't get this part. it supposed to be 24000 as we all know but i quoted this question from a classified questions book, and it seems to be a very old question. don't worry about that. Sure, i'll try to solve your questions, but can u link me to them?