acidic env. multiple choice (1 Viewer)

[VJ30]

Equal volumes of four 0.1 M acids were titrated with the same sodium hydroxide solution.
Which one requires the greatest volume of base to change the colour of the indicator?
(A) Citric acid
(B) Acetic acid
(C) Sulfuric acid
(D) Hydrochloric acid


i chose sulfuric since its the most acidic?

 

[john-doe]

Equal volumes of four 0.1 M acids were titrated with the same sodium hydroxide solution.
Which one requires the greatest volume of base to change the colour of the indicator?
(A) Citric acid
(B) Acetic acid
(C) Sulfuric acid
(D) Hydrochloric acid



i chose sulfuric since its the most acidic?

whats the answers?

 

[nerdasdasd]

Equal volumes of four 0.1 M acids were titrated with the same sodium hydroxide solution.
Which one requires the greatest volume of base to change the colour of the indicator?
(A) Citric acid
(B) Acetic acid
(C) Sulfuric acid
(D) Hydrochloric acid


i chose sulfuric since its the most acidic?

No, it is HCI, sulfuric acid only partially ionises in water. It has to undergo 2 stages in order to fully ionise. The question is considering the 1st ionisation.

 

[soloooooo]

I would go C as well as it is the most acidic.

 

[john-doe]

LOL it is 2010 hsc question 7... BOS says answer is A..dafuq??

 

[john-doe]

No, it is HCI, sulfuric acid only partially ionises in water. It has to undergo 2 stages in order to fully ionise. The question is considering the 1st ionisation.

i think in hsc coarse we assume that it ionises fully. thats why sometimes we get questions to calculate its ph from its concentration...

 

[tarod]

I'm pretty sure its A

All same molar concentration acids require the same volume of base.

Hence, Triprotic (Citric) > diprotic (sulfuric) > monoprotic (HCl and ethanoic) in terms of base needed.

 

[deswa1]

I'm pretty sure its A

All same molar concentration acids require the same volume of base.

Hence, Triprotic (Citric) > diprotic (sulfuric) > monoprotic (HCl and ethanoic) in terms of base needed.

Yeah this- its defs A. Write out the equation stoichometry between the NaOH base and the four acids and look at the relative moles of acid required and then you'll notice that citric (by virtue of being triprotic), requires three times the moles (and hence volume) of NaOH as HCl etc.

 

[barbernator]

a titration causes equilibrium reactions to go to completion. You don't have to worry about whether the molecule is fully ionised or not.

 

[someth1ng]

The correct answer is A.

Le Chatelier's principle: if a system is disturbed, the system's position of equilibrium will shift to partially counteract the imposed change, causing a new equilibrium to be established.

During titration, water is formed by the acid-base reaction causing H+ concentration to decrease and by Le Chatelier's principle, this will cause citric acid to further dissociate.

Dissociation of Citric Acid: C6H8O7 <--> 3H+ + C6H5O7 3- [All states aqueous]
Acid Base Reaction: H+ + OH- --> H2O [All ions are aqueous, water is liquid]

From the second equation, H+ concentration is decreasing due to the reaction, this causes H+ to decrease in the first equation and because it is an equilibrium system, it will favour the forward reaction as according to Le Chatelier's principle to oppose the imposed change.

In short, for titration questions, it's about the number of moles a single acid can produce (mono-, di- and triprotic), not its strength.

i think in hsc coarse we assume that it ionises fully. thats why sometimes we get questions to calculate its ph from its concentration...

Only for calculation questions such as determining pH.

 

[nerdasdasd]

http://wiki.answers.com/Q/Would_you..._a_stronger_or_a_weaker_acid_than_Acetic_acid

 

[nerdasdasd]

The pH of HCI will be lower.

 

[someth1ng]

As I said, it has nothing to do with the strength of the acid, one the hydrogen ion the acid releases is neutralised by the NaOH, it will create another hydrogen ion (Le Chatelier's principle) and that will keep occurring until there is no base left that can react.

Acid-base reaction ALWAYS go to completion but the strength of the acid and/or base will depend on how quickly the reaction goes.

 

[madharris]

I know it's already being said but basically just confirming what everyone else has stated

a) H3C6H5O7 + 3NaOH -----> Na3C6H5O7 + 3H20--molar ratio 1:3
b) CH3COOH + NaOH ----> NaCH3COO + H2O ------molar ratio 1:1
c) H2SO4 + 2NaOH ----> Na2SO4 + 2H2O -----------molar ratio 1:2
d) HCl + NaOH ----> NaCl + H2O ---------------------molar ratio 1:1

this means that citric acid needs the most base for a change in indiciator colour as it needs 3 times as much base as the acid.

Hope that helped

Edit: my spacing didn't work

 

[someth1ng]

nerdasdasd, are you now convinced?

 

[Sindivyn]

Can I just clarify something for this question? I understand that citric acid is triprotic, and therefore will take the longest to undergo complete reaction.
However, what I'm not completely sure about is the reason why it also takes the longest to cause the indicator to change colour. Is it because there are less ions in solution at any given time than a strong acid? Meaning rate of reaction is slowed due to less collisions.

Thanks

Edit: This is probably due to a lack of understanding titration graphs on my part

 

[barbernator]

Can I just clarify something for this question? I understand that citric acid is triprotic, and therefore will take the longest to undergo complete reaction.
However, what I'm not completely sure about is the reason why it also takes the longest to cause the indicator to change colour. Is it because there are less ions in solution at any given time than a strong acid? Meaning rate of reaction is slowed due to less collisions.

Thanks

its because when a base is added to a strong acid, the hydronium ions react directly with the hydroxide ions. In a strong base is added to a weak acid, firstly the hydronium ions will react, but then le chateliers principle will kick in causing the system to react and create more hydronium ions, and hence reacting with the hydroxide. Overall this will take longer because there are 2 reactions involved. its not really required to know though

 

[Sindivyn]

its because when a base is added to a strong acid, the hydronium ions react directly with the hydroxide ions. In a strong base is added to a weak acid, firstly the hydronium ions will react, but then le chateliers principle will kick in causing the system to react and create more hydronium ions, and hence reacting with the hydroxide. Overall this will take longer because there are 2 reactions involved. its not really required to know though

Yeah, that makes sense, thanks. For some reason I thought that weak acids would have steeper curves because they're weak. I wish they didn't call them strong/weak