Edexcel Unit 2 AS Chemistry - How did you find the exam?

Reply 60

Nautic4l

12

Original post by MoHoosen9167

Like this

Okay nvm 2nd one then

I am very scared now

Original post by Alfie_Francis

What did you guys say about the effect of changing PH on the equilibria reaction HOBr --><-- H+ + OBr- ?

Higher pH, less H+ so forward reaction is favoured to counteract the decrease in H+ concentration so equilibrium shifts to the right, reducing concentration of HOBr and increasing the concentration of OBr-

Reply 63

Alfie_Francis

Original post by MoHoosen9167

Nah, I said the Dichromate because the PCl5 doesn't confirm it's an alcohol it confirms the presence of an OH group.

I said Dichromate too but everybody else has said PCl5

Reply 64

C0balt

16

Original post by MoHoosen9167

Nah, I said the Dichromate because the PCl5 doesn't confirm it's an alcohol it confirms the presence of an OH group.

Dichromate doesn't confirm it is an alcohol either, it could've been aldehyde

Reply 65

MoHoosen9167

10

Original post by Nautic4l

Okay nvm 2nd one then

therereeeeeeeee

Screen Shot 2015-06-02 at 17.56.08.png12.7KB

Reply 66

MoHoosen9167

10

Original post by C0balt

Dichromate doesn't confirm it is an alcohol either, it could've been aldehyde

Yeah, but it works for primary and secondary alcohols, so there's a 2 in 3 chance for it to be an alcohol.

Reply 67

Alfie_Francis

Original post by C0balt

Higher pH, less H+ so forward reaction is favoured to counteract the decrease in H+ concentration so equilibrium shifts to the right, reducing concentration of HOBr and increasing the concentration of OBr-

I put that trend but I did not explain it :/ do you think there will be a mark for stating the trend?

Reply 68

Nautic4l

12

Original post by MoHoosen9167

therereeeeeeeee

Thank you

Reply 69

TheNervousWreck

13

Why did you wait 5 mins on the 1st question?
What was the bond angle? (AND HOW WAS THAT 5 MARKS????)
Why is CH4 more potent than CO2?

Reply 70

jshep000

OP

15

Original post by TheNervousWreck

Why did you wait 5 mins on the 1st question?
What was the bond angle? (AND HOW WAS THAT 5 MARKS????)
Why is CH4 more potent than CO2?

I put so it could all react but idk if that was right:/
Had to talk about the oxygen having 2 lone pairs of electrons, similar to H2O so 104.5 degrees. Maximum repulsion pushes the H and Cl down so the bond is smaller. Maximum repulsion etc
and I put the fact that CO2 could be removed or kept low by natural methods such a photosynthesis LOL, not too sure

Reply 71

C0balt

16

Original post by Alfie_Francis

I put that trend but I did not explain it :/ do you think there will be a mark for stating the trend?

Yeah should be
1 for talking about H+ concentration
1 for equilibrium change
1 for concentration of bromo species
I am guessing

Reply 72

JoeL66

1

I said PCl5 because the Br- is a reducing agent so would cancel out the effect of the potassium dichromate, this is wrong though, it's just all I could think up in the exam.

Reply 73

TheNervousWreck

13

Original post by jshep000

I put so it could all react but idk if that was right:/
Had to talk about the oxygen having 2 lone pairs of electrons, similar to H2O so 104.5 degrees. Maximum repulsion pushes the H and Cl down so the bond is smaller. Maximum repulsion etc
and I put the fact that CO2 could be removed or kept low by natural methods such a photosynthesis LOL, not too sure

LOL, I put, to make sure they all reached the same heat, I had no idea. I got the bond angle, PHEW. The CH4 one i said that it had more bonds, just made it up though.

Reply 74

1234560000000

allow all the solutions to reach the same temp to make it a fair test

104.5 degrees - 2 lone pairs 2 bind pairs, lone pairs repell mor ethan bond pairs, lone pair lone pair bond angles greater than bond pair bond pair angles, arranged for minimum repulsion, don't know it that is all 5

4 bonds per molecule whereas CO2 only 2 so can absorb more IR radiation per molecule

that's what i put

Reply 75

smcclelland24

Any one got the mark scheme???

Reply 76

MoHoosen9167

10

Original post by TheNervousWreck

Why did you wait 5 mins on the 1st question?
What was the bond angle? (AND HOW WAS THAT 5 MARKS????)
Why is CH4 more potent than CO2?

5 minutes: so that all of the testtubes can reach the same temperature.

Bond angle:
Dot Cross Diagramm
Bond angle 104.5
There are two lone pairs of electrons on the central oxygen atom, which causes maximum repulsion. The tetrahedral bond angle is distorted to a bent planar one, as each of the lone pairs reduces the bond angle by approximately 2.5 degrees. The unpaired electrons on the chlorine atom are disregarded as they are not on the central atom.

I don't know about CH4, I said because CH4 is formed by million year old plants but for some reason I confused potent with prominent

Reply 77

C0balt

16

Original post by TheNervousWreck

Why did you wait 5 mins on the 1st question?
What was the bond angle? (AND HOW WAS THAT 5 MARKS????)
Why is CH4 more potent than CO2?

Equal temperature for all test tubes to ensure fair test

- 104.5 degrees
- two bonding two lone pairs
- lone pair repel more
- position of minimum repulsion
- bent shape/based on tetrahedral /angle depression by 2.5 etc I think

CH4 has four polar bonds whereas CO2 only has two so more IR absorption

Reply 78

TheNervousWreck

13

Original post by 1234560000000

allow all the solutions to reach the same temp to make it a fair test

104.5 degrees - 2 lone pairs 2 bind pairs, lone pairs repell mor ethan bond pairs, lone pair lone pair bond angles greater than bond pair bond pair angles, arranged for minimum repulsion, don't know it that is all 5

4 bonds per molecule whereas CO2 only 2 so can absorb more IR radiation per molecule

that's what i put

I actually put all of the same......we either both got them right, or we are going down fighting together.

Reply 79

Alfie_Francis

Original post by TheNervousWreck

Why did you wait 5 mins on the 1st question?
What was the bond angle? (AND HOW WAS THAT 5 MARKS????)
Why is CH4 more potent than CO2?

CH4 is more potent as it has a higher relative greenhouse factor, it has 4 polar bonds per molecule whereas CO2 has 2 polar bonds per molecule, polar bonds absorb infra-red radiation and contribute to global warming

Edexcel Unit 2 AS Chemistry - How did you find the exam?

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