You are Here: Home

# Edexcel A2 Chemistry 6ch04/05 JUNE 2015 watch

Announcements
1. (Original post by frozo123)
Endothermic process

2H20---> H3O+ + OH-
so increasing the temperature will push equilibrium to the right
more oxonium ions so C?
I ticked C but it's A
2. (Original post by Ripper Phoenix)
no water will stay neutral no matter what happens. Answer is A
3. (Original post by Ripper Phoenix)
no water will stay neutral no matter what happens. Answer is A
any reasoning for that?
or is this one of those things we just gotta know?
4. (Original post by neverstop)
Hey guys , can someone help me with June 2014 - the equilibrium calculation ??? thanks
so starting at 12bii.
1. calculate moles of NaOH in test tube 1
77.1x0.2/1000=0.01542
2 calculate moles of NaOH that reacts with HCl
11.7x0.2/1000=0.00234
3. find the moles of ethanoic acid that didnt react
0.01542-0.00234=0.01308
so eqm moles of ethanoic acid is 0.01308

part iii.
ethanoic acid : ethanol is 1:1 ratio so eqm moles of ethanol is also 0.01308

part iv
1. find moles of ester
0.04-0.01308= 0.02692
5. (Original post by bbyturtlexox)
no, that's what I picked and that's what the text book says but it's A :s
just read this on chemguide it says : although the pH of pure water changes with temperature, it is important to realise that it is still neutral. In the case of pure water, there are always going to be the same number of hydrogen ions and hydroxide ions present. That means that the pure water remains neutral - even if its pH changes.
6. (Original post by bbyturtlexox)
Attachment 423365could someone please explain this to me the answer contradicts what is said in the text book
lol that question is bs cus someone just posted this mcq
At 100°C, pure water has a pH of 6, whereas at 25°C it has a pH of 7. This is because

A the dissociation of water is endothermic, so the concentration of hydrogen ions is lower at 100 °C than it is at 25 °C.
B the dissociation of water is exothermic, so the concentration of hydrogen ions is lower at 100°C than it is at 25°C.
C the dissociation of water is endothermic, so the concentration of hydrogen ions is higher at 100 °C than it is at 25 °C.
D at 100 °C, water has a higher concentration of hydrogen ions than of hydroxide ions.

and it says the pH is 6?
Unless it means conc of OH- will equal the conc of H+, then fair enough
7. okay so neutral is just defined as equal concentrations of hydrogen ions and hydroxide ions..

(Original post by Maham88)
just read this on chemguide it says : although the pH of pure water changes with temperature, it is important to realise that it is still neutral. In the case of pure water, there are always going to be the same number of hydrogen ions and hydroxide ions present. That means that the pure water remains neutral - even if its pH changes.
8. (Original post by MeeraP07)
So what you do first is find the difference between the inital moles and equilibrium moles of the carboxylic acid by doing 0.4-0.2=0.2

to find the eqm moles of alcohol you do the inital moles of alcohol- difference so 0.3-0.2=0.1

to find the eqm moles of the products you do inital moles+difference

ester- 0+0.2=0.2
water-0.15+0.2=0.35

and then you plug these values into Kc
THank you! And another rates question:

Sulfuryl chlorie decomposes in a first order reaction. The half-life for this reaction is 2300s. In an experiment, the initial concentration of sulfuryl chloride is 1.0 mol dm^-3. What is the concentration of sulfuryl chloride after 4600 s?

a) 0.75
b) 0.50
c) 0.25
d) 0.125

9. (Original post by bbyturtlexox)
what's the difference between thermo dynamic stability and kinetic inertness.

I think thermodynamics is to do with enthalpy change and kinetics is to do with activation energy and rate of the reaction.. is this correct?
thermodynamic stability- no tendency for a reaction to occur
kinetically inert- a reaction doesnt occur despite seeming feasible due to high activation energy
10. (Original post by sj97)
THank you! And another rates question:

Sulfuryl chlorie decomposes in a first order reaction. The half-life for this reaction is 2300s. In an experiment, the initial concentration of sulfuryl chloride is 1.0 mol dm^-3. What is the concentration of sulfuryl chloride after 4600 s?

a) 0.75
b) 0.50
c) 0.25
d) 0.125

you start off at t=0 with 1.0
at t=2300 0.5
at t= 4600 0.25
11. (Original post by MeeraP07)
thermodynamic stability- no tendency for a reaction to occur
kinetically inert- a reaction doesnt occur despite seeming feasible due to high activation energy
can we deduce anything from just the enthalpy change of the reaction?
12. (Original post by sj97)
THank you! And another rates question:

Sulfuryl chlorie decomposes in a first order reaction. The half-life for this reaction is 2300s. In an experiment, the initial concentration of sulfuryl chloride is 1.0 mol dm^-3. What is the concentration of sulfuryl chloride after 4600 s?

a) 0.75
b) 0.50
c) 0.25
d) 0.125

At the half life of 2300s there is 0.5moldm-3 (1 divided by 2)
since it is 1st order the half lives are constant
at 4600s it is 0.25moldm-3 (0.5 divided by 2) (4600 is double 2300)

I hope that made sense its kinda difficult to explain haha
13. (Original post by Nautic4l)
http://qualifications.pearson.com/co...e_20120307.pdf

See now I don't get 9? I thought it was B
Br is the priory group on the right hand side because it has a higher atomic number than carbon in the CH3. Both priority groups are on the top (the same size) so it has to be Z and therefore the answer is A.

Try this link it should help http://www.chemguide.co.uk/basicorg/isomerism/ez.html
14. (Original post by bbyturtlexox)
bronsted Lowry
Thanks.

Posted from TSR Mobile
15. (Original post by MeeraP07)
so starting at 12bii.
1. calculate moles of NaOH in test tube 1
77.1x0.2/1000=0.01542
2 calculate moles of NaOH that reacts with HCl
11.7x0.2/1000=0.00234
3. find the moles of ethanoic acid that didnt react
0.01542-0.00234=0.01308
so eqm moles of ethanoic acid is 0.01308

part iii.
ethanoic acid : ethanol is 1:1 ratio so eqm moles of ethanol is also 0.01308

part iv
1. find moles of ester
0.04-0.01308= 0.02692
Hi thanks so much but I don't understand why you have to workout moles of NaOH reacting with the HCL ? Why can't I just use the moles of NaOH with the contents of the first test tube? Also, I don't understand the purpose of the second test tube?
16. Hi , can someone help me with question 2 June 2014 GCE multiple choice part (c) and (d) why is the answer to (c) not A if the reaction is second order? And i'm not so sure about the reasoning behind part (d) . Thanks !
17. (Original post by Maham88)
is it c ?
H+ and OH- are always equal in water , you know this from the dissociation constant for kW, therefore they cancel each other out and water remains neutral when it dissociates
18. For this question:

To work out the gradient, which values would be y values and which would be on the x values? If you were to plot this table, is there a rule for which axis these go on?
19. Endothermic, so when temperature increases, water dissociates more:

H2O ----> H+ + OH-
Equilibrium is shifted to the right, so a greater yield of BOTH H+ and OH-, me thinks. So all in all, water remains neutral!
20. (Original post by laurenjjj)
For this question:

To work out the gradient, which values would be y values and which would be on the x values? If you were to plot this table, is there a rule for which axis these go on?
ln(1/t) would be on the y-axis going down (as it is negative).
1/T would be on the x-axis.

Gradient= change in y/change in x

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 3, 2016
Today on TSR

### Lied on my UCAS

And my school told me not to change it

### University open days

• University of Derby
Tue, 22 Jan '19
• University of the West of England, Bristol
Wed, 23 Jan '19
• University of East London
Wed, 23 Jan '19
Poll
Useful resources

Can you help? Study Help unanswered threadsStudy help rules and posting guidelines

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE