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

Reply 664

Maham88

2

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.

Reply 665

frozo123

12

Original post by bbyturtlexox

could someone please explain this to me :s-smilie:

the answer contradicts what is said in the text book :colonhash:

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

Reply 666

bbyturtlexox

12

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.

Reply 667

sj97

3

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

The answer is C. Please explain? Wouldn't it be B?

Reply 668

MeeraP07

7

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

Reply 669

frozo123

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

The answer is C. Please explain? Wouldn't it be B?

you start off at t=0 with 1.0
at t=2300 0.5
at t= 4600 0.25

Reply 670

frozo123

12

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?

Reply 671

MeeraP07

7

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

The answer is C. Please explain? Wouldn't it be B?

The answer is C because...
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

Reply 672

cathalmcc

Original post by Nautic4l

http://qualifications.pearson.com/content/dam/pdf/A%20Level/Chemistry/2013/Exam%20materials/6CH04_01_que_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

Reply 673

Wannabe007

2

Original post by bbyturtlexox

bronsted Lowry

Thanks.

Posted from TSR Mobile

Reply 674

neverstop

2

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?

Reply 675

neverstop

2

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 !

Reply 676

cathalmcc

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

Reply 677

laurenjjj

8

For this question: Screen Shot 2015-06-09 at 15.41.15.png

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?

Reply 678

AffirmedCube

9

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! :biggrin:

Reply 679

AffirmedCube

9

Original post by laurenjjj

For this question: Screen Shot 2015-06-09 at 15.41.15.png

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 :smile:

Edexcel A2 Chemistry 6ch04/05 JUNE 2015

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you