Chemistry: Post your doubts here!

[Xylferion]

Can anyone explain to me these few questions?

1. The density of ice is 1.00gcm-3. What is the volume of steam produced when 1.00cm3 of ice is heated to 323 degree celcius (596K) at a pressure of one atm (101 kPa) [ 1 mol of gas occupies 24.0dm3 at 25 degree celcius (298K) and one atm.
Ans: 2.67 dm3

2.Which of the following would behave most like an ideal gas at room temp?
Ans: Helium (Why Helium not Hydrogen?)

3. What are the assumptions of the kinetic theory of gases and hence of the ideal gas equation, PV= nRT?
Ans: molecules move without interacting with one another except for collisions ( Why does this statement mean?)

4. When a sample of gas is compressed at constant temp from 1500 kPa to 6000 kPa, its volume changes from 76.0cm3 to 20.5 cm3. Which statement are possible explanations for this behavior?
Wrong ans: The gas partially liquefies / Gas is absorbed on to the vessel walls ( Why)?

Thank You.!

1) Use the density and volume to find the mass.

Mass of ice = 1.00 gcm-3 * 1.00 cm3 = 1.00 g
Moles of ice ( ice is frozen water aka H2O ) = 1/18 = 0.0556 moles

It says there in bracket, the volume 1 mol of gas occupies at 298K is 24dm^3.
So 0.0556 moles will give 1.33 dm^3.

This is at 298 K, but we want 596K.

298K = 1.33 dm^3
596K = x
298K * x = 1.33 * 596
298K * x = 792.68
x = 2.66 dm^3
--------------------------------

2) Helium has a complete outers hell and is probably the most inert ( not reactive ) of all the noble gases. A possibility of it bonding with other atoms does not exist. For hydrogen however, it seeks to achieve a noble state, so it does have the possibility of bonding with other atoms. For that reason alone, Helium is more ideal. Ideal gases are based off of the assumption that there are no forces of attraction at all between the gas particles.
--------------------------

3) Like I said above, ideal gases are said to not posses any forces of attraction between the molecules, as a result of this, you find them colliding with each other constantly, so there's hardly anytime for the possibility of attraction between the molecules. The term "interact" means there are forces at work, which isn't the case with ideal gases.
-----------------------

4) You're going to need far more than 6k Pa in order to initiate a partial change in state. The question specifically mentions " constant temperature ", which means that the container and surroundings of the gas molecules isn't going to get any cooler.
This doesn't allow for condensation to take place that easily.
It's also worth noting that the particles are now moving about randomly and colliding with the container much more, "colliding". They can't be absorbed if they're going to collide and then resume moving about.

Hope any of that made sense!

 

[Xylferion]

Guys, I am struggling with this question!!!! :'(

It's May June 2014, 23 Question 1 (b) (v)

(v) Deduce the values of x, y and z in the equation in (iv)

PLEASE HELP!!!http://maxpapers.com/wp-content/uploads/2012/11/9701_s14_qp_23.pdf

A few key things to note, the gas volumes were measured at 298K and 100 kPa. These are standard conditions. What this means is that the products will have H2O as a liquid. So you can ignore its volume.

CxHy + O2 -----> CO2 + zH2O

First thing you need to know, x moles of C on the left will give x moles of C on the right.

CxHy + O2 ----> xCO2 + zH2O

Next, y moles of H on the left will give z moles of H on the right. Since z = 2H atoms, and since z = y, it will give y/2 H atoms on the right.

CxHy + O2 -----> xCO2 + y/2 H2O

You start off with 10 cm3 of CxHy, and 100 cm3 of O2.

Final volume = 95 cm3. This volume accounts for "unreacted" oxygen and CO2. Since we do not consider the volume of H2O. The unreacted oxygen is because the question mentioned that we used "excess" oxygen.

So 95 cm3 = CO2 + Unreacted O2

They say the CO2 is absorbed by NaOH, and it becomes 75 cm3.
That means the volume of CO2 is 20 cm3.
75 cm3 of Unreacted oxygen is left from 100cm3 used. So we used 25 cm3.

This gives you the following ratios:

CxHy : O2 : CO2 : H2O
10 : 25 : 20 : X
Simplifies to, 1 : 2.5 : 2

So 1 CxHy + 2.5 O2 ----> 2CO2 + H2O
Like above, CxHy ---> xCO2
Which is 2 in this case, so now you have:

C2Hy + 2.5O2 ---> 2CO2 + H2O

Now tackle the oxygens, there's 5 moles on the left. There has to be 5 on the right. Which there are so you end up with:

C2Hy + 2.5 O2 ----> 2CO2 + 1H2O

2 moles of H2 on the right, so there has to be 2 on the left.
Giving you C2H2.

x = 2
y = 2
z = 1

However since they don't like having decimals for values,

It becomes 2 C2H2 + 5 O2 ---> 4CO2 + 2H2O

x=2, y=2, z=2.

They did mention that putting z as 1 is acceptable though.

Hope that helped!

 

[Studydayandnight]

O

A few key things to note, the gas volumes were measured at 298K and 100 kPa. These are standard conditions. What this means is that the products will have H2O as a liquid. So you can ignore its volume.

CxHy + O2 -----> CO2 + zH2O

First thing you need to know, x moles of C on the left will give x moles of C on the right.

CxHy + O2 ----> xCO2 + zH2O

Next, y moles of H on the left will give z moles of H on the right. Since z = 2H atoms, and since z = y, it will give y/2 H atoms on the right.

CxHy + O2 -----> xCO2 + y/2 H2O

You start off with 10 cm3 of CxHy, and 100 cm3 of O2.

Final volume = 95 cm3. This volume accounts for "unreacted" oxygen and CO2. Since we do not consider the volume of H2O. The unreacted oxygen is because the question mentioned that we used "excess" oxygen.

So 95 cm3 = CO2 + Unreacted O2

They say the CO2 is absorbed by NaOH, and it becomes 75 cm3.
That means the volume of CO2 is 20 cm3.
75 cm3 of Unreacted oxygen is left from 100cm3 used. So we used 25 cm3.

This gives you the following ratios:

CxHy : O2 : CO2 : H2O
10 : 25 : 20 : X
Simplifies to, 1 : 2.5 : 2

So 1 CxHy + 2.5 O2 ----> 2CO2 + H2O
Like above, CxHy ---> xCO2
Which is 2 in this case, so now you have:

C2Hy + 2.5O2 ---> 2CO2 + H2O

Now tackle the oxygens, there's 5 moles on the left. There has to be 5 on the right. Which there are so you end up with:

C2Hy + 2.5 O2 ----> 2CO2 + 1H2O

2 moles of H2 on the right, so there has to be 2 on the left.
Giving you C2H2.

x = 2
y = 2
z = 1

However since they don't like having decimals for values,

It becomes 2 C2H2 + 5 O2 ---> 4CO2 + 2H2O

x=2, y=2, z=2.

They did mention that putting z as 1 is acceptable though.

Hope that helped!

Thank you so much! You have no idea how grateful I am to you for solving this step by step! THANK YOU!!!!

 

[Xylferion]

O


Thank you so much! You have no idea how grateful I am to you for solving this step by step! THANK YOU!!!!

No problem at all, Happy I could help!

 

[asadalam]

Xylferion You giving AS this session?

 

[Xylferion]

Xylferion You giving AS this session?

Yeah.

 

[asadalam]

Yeah.

Only AS or A2 as well?

 

[Xylferion]

Only AS or A2 as well?

Just AS.

 

[Metanoia]

Can anyone explain to me these few questions?
4. When a sample of gas is compressed at constant temp from 1500 kPa to 6000 kPa, its volume changes from 76.0cm3 to 20.5 cm3. Which statement are possible explanations for this behavior?
Wrong ans: The gas partially liquefies / Gas is absorbed on to the vessel walls ( Why)?

Thank You.!

I'll add on to the explanation of question 4.

ASSUMING that the gas was an ideal gas.

P1V1 = P2V2
(1500)(76) = (6000)(V2)
V2 = 19 cm^3

This means that if it was an ideal gas, the volume is expected to be 19 cm^3. However, the actual observed volume is 20.5 cm^3.

Since it turned out that the actual volume is MORE than expected, we can't use the possibility that part of the gas became liquid.

Conversely, if the actual volume is less than expected, then it is possible to use the explanation that part of the gas liquifies or is absorbed on walls of vessels.

 

[princess Anu]

It seems correct to me, as for balancing of the stuff in the box it's better to do it but it won't affect your answer.

but how do I balance it? there is no O in the above equation :S

 

[qwertypoiu]

but how do I balance it? there is no O in the above equation :S

Balance everything except the O's, those are essentially coming from combustion. In energy cycles, from my experience so far, one should balance everything like hydrogen, carbon, etc. but oxygen may be ignored.
However, if you really wish, you can add oxygen on both sides above. Oxygen doesn't have enthalpy change of combustion I think, and it's enthalpy change of formation is 0.

 

[Midnight dream]

http://maxpapers.com/syllabus-materials/chemistry-9701-a-level/attachment/9701_w09_qp_21/
Can anyone explain question 3 c?

 

[Lola_sweet]

Can someone please explain this statement:

Student X claimed tht the 17 carbon atoms in the four rings lie all in the same plane

 

[forest822]

1) Use the density and volume to find the mass.

Mass of ice = 1.00 gcm-3 * 1.00 cm3 = 1.00 g
Moles of ice ( ice is frozen water aka H2O ) = 1/18 = 0.0556 moles

It says there in bracket, the volume 1 mol of gas occupies at 298K is 24dm^3.
So 0.0556 moles will give 1.33 dm^3.

This is at 298 K, but we want 596K.

298K = 1.33 dm^3
596K = x
298K * x = 1.33 * 596
298K * x = 792.68
x = 2.66 dm^3
--------------------------------

2) Helium has a complete outers hell and is probably the most inert ( not reactive ) of all the noble gases. A possibility of it bonding with other atoms does not exist. For hydrogen however, it seeks to achieve a noble state, so it does have the possibility of bonding with other atoms. For that reason alone, Helium is more ideal. Ideal gases are based off of the assumption that there are no forces of attraction at all between the gas particles.
--------------------------

3) Like I said above, ideal gases are said to not posses any forces of attraction between the molecules, as a result of this, you find them colliding with each other constantly, so there's hardly anytime for the possibility of attraction between the molecules. The term "interact" means there are forces at work, which isn't the case with ideal gases.
-----------------------

4) You're going to need far more than 6k Pa in order to initiate a partial change in state. The question specifically mentions " constant temperature ", which means that the container and surroundings of the gas molecules isn't going to get any cooler.
This doesn't allow for condensation to take place that easily.
It's also worth noting that the particles are now moving about randomly and colliding with the container much more, "colliding". They can't be absorbed if they're going to collide and then resume moving about.

1) Use the density and volume to find the mass.

Mass of ice = 1.00 gcm-3 * 1.00 cm3 = 1.00 g
Moles of ice ( ice is frozen water aka H2O ) = 1/18 = 0.0556 moles

It says there in bracket, the volume 1 mol of gas occupies at 298K is 24dm^3.
So 0.0556 moles will give 1.33 dm^3.

This is at 298 K, but we want 596K.

298K = 1.33 dm^3
596K = x
298K * x = 1.33 * 596
298K * x = 792.68
x = 2.66 dm^3
--------------------------------

2) Helium has a complete outers hell and is probably the most inert ( not reactive ) of all the noble gases. A possibility of it bonding with other atoms does not exist. For hydrogen however, it seeks to achieve a noble state, so it does have the possibility of bonding with other atoms. For that reason alone, Helium is more ideal. Ideal gases are based off of the assumption that there are no forces of attraction at all between the gas particles.
--------------------------

3) Like I said above, ideal gases are said to not posses any forces of attraction between the molecules, as a result of this, you find them colliding with each other constantly, so there's hardly anytime for the possibility of attraction between the molecules. The term "interact" means there are forces at work, which isn't the case with ideal gases.
-----------------------

4) You're going to need far more than 6k Pa in order to initiate a partial change in state. The question specifically mentions " constant temperature ", which means that the container and surroundings of the gas molecules isn't going to get any cooler.
This doesn't allow for condensation to take place that easily.
It's also worth noting that the particles are now moving about randomly and colliding with the container much more, "colliding". They can't be absorbed if they're going to collide and then resume moving about.

Hope any of that made sense!

Thank you for the solution. May I know what is the condition that gas will be absorbed on to the vessel wall?

 

[qwertypoiu]

Can someone please explain this statement:

Student X claimed tht the 17 carbon atoms in the four rings lie all in the same plane

A plane refers to a 2D surface at a certain angle, like one face of a cuboid.I don't know if this makes sense, I don't know how to explain a plane in writing, so here's a picture:

The points A, B, and C are on the same plane, meaning they are on the same SURFACE.

For example, the carbon atoms in one layer of graphite lies on one plane.

I have seen the question you are talking about.
The student X claims that all these 17 carbons are lying in one particular plane, it cannot be true, since the carbons are sp3 hybridised and so bonded to 4 groups each, which means it will form a 3D shape with 109.5 degrees as the bond angle, which is NOT in one plane.

 

[Lola_sweet]

A plane refers to a 2D surface at a certain angle, like one face of a cuboid.I don't know if this makes sense, I don't know how to explain a plane in writing, so here's a picture:

The points A, B, and C are on the same plane, meaning they are on the same SURFACE.

For example, the carbon atoms in one layer of graphite lies on one plane.

I have seen the question you are talking about.
The student X claims that all these 17 carbons are lying in one particular plane, it cannot be true, since the carbons are sp3 hybridised and so bonded to 4 groups each, which means it will form a 3D shape with 109.5 degrees as the bond angle, which is NOT in one plane.

Thank u so much

 

[Midnight dream]

A plane refers to a 2D surface at a certain angle, like one face of a cuboid.I don't know if this makes sense, I don't know how to explain a plane in writing, so here's a picture:

The points A, B, and C are on the same plane, meaning they are on the same SURFACE.

For example, the carbon atoms in one layer of graphite lies on one plane.

I have seen the question you are talking about.
The student X claims that all these 17 carbons are lying in one particular plane, it cannot be true, since the carbons are sp3 hybridised and so bonded to 4 groups each, which means it will form a 3D shape with 109.5 degrees as the bond angle, which is NOT in one plane.

And also in the same question, it was asked whether the compound exhibits cis-trans isomerism. And the answer was No. So does it mean that cyclic alkenes never exhibit isomerism?

 

[forest822]

Hello. Can anyone please explain to me these questions? Thank you

1. The density of this nitrogen to be 1.2572gdm-3 at stp. Chemically, pure nitrogen has a density of 1.2505gdm-3 at stp. Which gas was present in atmospheric nitrogen to cause this discrepancy?
A. Argon B. Helium C. Methane D. Neon. ANS: Argon (Why?)

2. A sample of mg of an organic compound is vaporised in a gas syringe and occupies V cm3 at TK and p atm. What is the relative molecular mass of the compound, Mr?
A. Mr= (m.22400.T)/p.V.273 B. Mr= (m.22400.T+273)/p.V.273 C. Mr= (m.22400.273.p)/V.T D. (m.22400.273.p)/V.(T+273) ANS: A

 

[qwertypoiu]

And also in the same question, it was asked whether the compound exhibits cis-trans isomerism. And the answer was No. So does it mean that cyclic alkenes never exhibit isomerism?

No. Cycloalkenes are restricted from having cis-trans isomers, but those which have more than 8 carbons DO have cis-trans isomerism.
Metanoia Please confirm this is true right??

 

[Midnight dream]

http://maxpapers.com/syllabus-materials/chemistry-9701-a-level/attachment/9701_w09_qp_21/
Xylferion Please can you answer 3 part c?