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Chemistry: Post your doubts here!

princess Anu

princess Anu

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Metanoia said:
When there are more than 1 functional groups, there is a need to rank the functional groups.

http://www.masterorganicchemistry.co...-nomenclature/
Click to expand...
suppose if there is a compound with carboxylic acid and ketone group.. so I'll try to name as such both the functional groups are a part of the longest chain..? and if thats not possible, at least carboxylic acid should be .. right?

Moreover what's the use of the prefix??? for example ester prefix is ''oxycarbonyl'' and aldehyde's is OXO but we do not use these terms to name esters/aldehydes right? so what is their purpose
 
Metanoia

Metanoia

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princess Anu said:
suppose if there is a compound with carboxylic acid and ketone group.. so I'll try to name as such both the functional groups are a part of the longest chain..? and if thats not possible, at least carboxylic acid should be .. right?

Moreover what's the use of the prefix??? for example ester prefix is ''oxycarbonyl'' and aldehyde's is OXO but we do not use these terms to name esters/aldehydes right? so what is their purpose
Click to expand...

If there is a carboxylic acid and ketone group, the carboxylic acid is of a higher rank. The parent (longest) chain must contain carboxylic acid (and not necessary the ketone group).

Prefixes are used when there are more than 1 functional groups, I'll use alcohol to explain the idea of the prefix.

If alcohol is the highest ranked group, the molecule will be named as "-ol".

If alcohol is not the highest ranked group among the functional groups (e.g. alcohol and ketone), the prefix of alcohol (hydroxyl) would be used instead.
imgf000004_0002.png

hydroxyl -ketone molecule


Additional point, you made mistake in naming the prefix of aldehyde as "oxo".
Prefix of aldehyde is formyl and prefix of ketones is oxo.
Having said that, it is unlikely that students are required to memorize the ranking to name complicated molecules.
 
Xylferion

Xylferion

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princess Anu said:
In the reaction of HCN with Carbonyl compounds, we use NaCN as a catalyst or as a source of CN- ions?

While making displayed formula, do we have to take care of making the right structure with the correct bond angles too? for example in J10/23Q5 part a, the structure given in the Marking scheme is absolutely perfect in terms of the bond angles etc but when I make displayed formulas generally I tend to just display all the bonds ( not caring about the bond angles)
So is my method acceptable?
Click to expand...

CN- acts as the catalyst, NaCN is just there as a provider.

NaCN ----> Na + and CN-
 
princess Anu

princess Anu

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is my cycle correct? (particularly the highlighted part) and do we need to balance it?
 

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forest822

forest822

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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.!
 
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Jewel504

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Hey can someone pls explain the answer to question 5 may/june year 2012 paper 2 qp 21
 
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Xylferion

Xylferion

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forest822 said:
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.!
Click to expand...

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! (y)
 
Xylferion

Xylferion

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Studydayandnight said:
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
Click to expand...

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!
 
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Studydayandnight

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O
Xylferion said:
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!
Click to expand...

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