The rate of the reaction with methanoic acid is greater than the rate of the reaction

Watch
S551
Badges: 3
Rep:
?
#1
Report Thread starter 1 month ago
#1
The student compares the rates of the reaction of zinc carbonate with:
• 0.01 mol/dm3 methanoic acid
• 0.01 mol/dm3 ethanoic acid.
The rate of the reaction with methanoic acid is greater than the rate of the reaction
with ethanoic acid.
Explain why.
You should refer to ions in your answer.Name:  Screenshot 2021-05-09 130915.png
Views: 36
Size:  108.1 KB
Last edited by S551; 1 month ago
0
reply
charco
Badges: 17
Rep:
?
#2
Report 1 month ago
#2
(Original post by S551)
The student compares the rates of the reaction of zinc carbonate with:
• 0.01 mol/dm3 methanoic acid
• 0.01 mol/dm3 ethanoic acid.
The rate of the reaction with methanoic acid is greater than the rate of the reaction
with ethanoic acid.
Explain why.
You should refer to ions in your answer.Name:  Screenshot 2021-05-09 130915.png
Views: 36
Size:  108.1 KB
I've read the instructions - very nice but ...
What's your question?
0
reply
S551
Badges: 3
Rep:
?
#3
Report Thread starter 1 month ago
#3
(Original post by charco)
I've read the instructions - very nice but ...
What's your question?
why is the rate of the reaction with methanoic acid greater than the rate of reaction with ethanoic acid?
0
reply
charco
Badges: 17
Rep:
?
#4
Report 1 month ago
#4
(Original post by S551)
why is the rate of the reaction with methanoic acid greater than the rate of reaction with ethanoic acid?
It's a stronger acid ...
0
reply
bxaanca
Badges: 11
Rep:
?
#5
Report 1 month ago
#5
(Original post by S551)
The student compares the rates of the reaction of zinc carbonate with:
• 0.01 mol/dm3 methanoic acid
• 0.01 mol/dm3 ethanoic acid.
The rate of the reaction with methanoic acid is greater than the rate of the reaction
with ethanoic acid.
Explain why.
You should refer to ions in your answer.Name:  Screenshot 2021-05-09 130915.png
Views: 36
Size:  108.1 KB
idk but i think that because ethanoic has an alkyl group that pushes its electron density which makes the carboxylate (-COO group) less stable, making it less likely to dissociate the H+ ion.
0
reply
charco
Badges: 17
Rep:
?
#6
Report 1 month ago
#6
(Original post by bxaanca)
idk but i think that because ethanoic has an alkyl group that pushes its electron density which makes the carboxylate (-COO group) less stable, making it less likely to dissociate the H+ ion.
This is not correct.

Methanoic acid is more acidic as the conjugate base, the methanoate ion is not destabilised by the +I effect of an alkyl group attached to the carboxylate group.

The alkyl group increases the electron density of the OH group in ethanoic acid increasing its strength also contributing to the decreased acidity of ethanoic acid.
0
reply
bxaanca
Badges: 11
Rep:
?
#7
Report 1 month ago
#7
(Original post by charco)
This is not correct.

Methanoic acid is more acidic as the conjugate base, the methanoate ion is not destabilised by the +I effect of an alkyl group attached to the carboxylate group.

The alkyl group increases the electron density of the OH group in ethanoic acid increasing its strength also contributing to the decreased acidity of ethanoic acid.
there isn't an alkyl group attached to methanoate though?
it's just HCOOH or correct me if i'm wrong please
0
reply
charco
Badges: 17
Rep:
?
#8
Report 1 month ago
#8
(Original post by bxaanca)
there isn't an alkyl group attached to methanoate though?
it's just HCOOH or correct me if i'm wrong please
Yes, you are correct. That is why I said that it is NOT destabilised by the +I effect of an alkyl group, while ethanoic acid is.
0
reply
alexs2005
Badges: 1
Rep:
?
#9
Report 4 weeks ago
#9
I think its because ethane is a larger hydrocarbon molecule compared to methane, therefore has stronger intermolecular forces. More energy is needed to over come ethane (higher b.p). This also makes it less volatile, therefore less flammable. This means that Methanolic acid has a higher rate of reaction as its ions are weaker, having weaker intermolecular forces, so not a lot of energy is needed to over come.

Hope this kinda helps
Last edited by alexs2005; 4 weeks ago
0
reply
mandyelicup
Badges: 12
Rep:
?
#10
Report 4 weeks ago
#10
(Original post by S551)
The student compares the rates of the reaction of zinc carbonate with:
• 0.01 mol/dm3 methanoic acid
• 0.01 mol/dm3 ethanoic acid.
The rate of the reaction with methanoic acid is greater than the rate of the reaction
with ethanoic acid.
Explain why.
You should refer to ions in your answer.Name:  Screenshot 2021-05-09 130915.png
Views: 36
Size:  108.1 KB
I think it's a gcse question right?
So, methanoic acid is a stronger acid. It dissociates in aqueous solution more fully into H+ ions (reference the numbers in the table) than ethanoic acid so has a higher H+ ion concentration. Therefore it reacts at a greater rate with zinc carbonate (greater rate of production of CO2)
Last edited by mandyelicup; 4 weeks ago
0
reply
bxaanca
Badges: 11
Rep:
?
#11
Report 4 weeks ago
#11
(Original post by mandyelicup)
I think it's a gcse question right?
So, methanoic acid is a stronger acid. It dissociates in aqueous solution more fully into H+ ions (reference the numbers in the table) than ethanoic acid so has a higher H+ ion concentration. Therefore it reacts at a greater rate with zinc carbonate (greater rate of production of CO2)
arent carboxylic acids weak? so not complete dissociation
0
reply
mandyelicup
Badges: 12
Rep:
?
#12
Report 4 weeks ago
#12
(Original post by bxaanca)
arent carboxylic acids weak? so not complete dissociation
yeah but I think methanoic dissociates more completely so higher H+ ion concentration
0
reply
bxaanca
Badges: 11
Rep:
?
#13
Report 4 weeks ago
#13
(Original post by mandyelicup)
yeah but I think methanoic dissociates more completely so higher H+ ion concentration
no such thing as 'more completely'. weak acids never fully dissociate their H+ that's why they're weak.
0
reply
charco
Badges: 17
Rep:
?
#14
Report 4 weeks ago
#14
(Original post by bxaanca)
no such thing as 'more completely'. weak acids never fully dissociate their H+ that's why they're weak.
He/she just meant "more".

Methanoic acid (pka = 3.75) dissociates more than ethanoic acid (pka = 4.75).

It provides a higher concentration of hydrogen ions (for equal acid concentrations) and reacts faster with bases.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Do you think receiving Teacher Assessed Grades will impact your future?

I'm worried it will negatively impact me getting into university/college (69)
37.7%
I'm worried that I’m not academically prepared for the next stage in my educational journey (18)
9.84%
I'm worried it will impact my future career (12)
6.56%
I'm worried that my grades will be seen as ‘lesser’ because I didn’t take exams (45)
24.59%
I don’t think that receiving these grades will impact my future (24)
13.11%
I think that receiving these grades will affect me in another way (let us know in the discussion!) (15)
8.2%

Watched Threads

View All