Titration Question (2 Viewers)

[Ekman]

Hey everyone I had my chemistry exam today and there was a question I had issues with. Here it is:

A student took a sample of sulphuric acid from a large car battery spill near a park. A standard solution was prepared using sodium carbonate. 25mL of sulphuric acid was added to the burette. 25mL was pipetted from the standard solution and placed into a conical flask.

Now here is the interesting bit.

The student realized that the pipette was leaking during the transfer of the standard solution into the conical flask. What impacts will this have on the calculated concentration of sulphuric acid in comparison to its true concentration.

 

[Librah]

More, if it spilled, there will be less moles in the flask, and less volume of acid will be required to neutralize the base, so your calculated concetration will be greater.

 

[Ekman]

Less, if it spilled, your losing moles of acid, which means less base will be required to be required to neutralize the acid, so your calculated value for acid conc will be lower.

Are you talking about the base? Since the acid is in the burette and the base is the one being pipetted, and the unknown is the acid.

 

[Librah]

Are you talking about the base? Since the acid is in the burette and the base is the one being pipetted, and the unknown is the acid.

wait, in that case the calculated h2so4 conc will be higher. Misread question.

 

[InteGrand]

Hey everyone I had my chemistry exam today and there was a question I had issues with. Here it is:

A student took a sample of sulphuric acid from a large car battery spill near a park. A standard solution was prepared using sodium carbonate. 25mL of sulphuric acid was added to the burette. 25mL was pipetted from the standard solution and placed into a conical flask.

Now here is the interesting bit.

The student realized that the pipette was leaking during the transfer of the standard solution into the conical flask. What impacts will this have on the calculated concentration of sulphuric acid in comparison to its true concentration.

 

[Ekman]

Ok thanks guys, this is exactly what I said in the exam, however my teacher claims that it would be decrease, because apparently in the formula c=n/v, the volume remains constant however the moles decrease and hence the concentration would decrease. However I am going to show Q28 in the 2013 HSC exam, which is a similar question, tomorrow in order to prevent me from losing a mark.

 

[Drsoccerball]

If there pipette is leaking the amount of H2SO4 decreases therefore less of the standard is required to titrate it. If less is required to titrate it, it must be less concentration ? im pretty sure our teachers right

 

[Ekman]

Also one question, can we assume that the number of moles is constant as the student did not realize it was leaking till after the experiment, so if we use the formula:



We basically prove it mathematically, as less volume is needed, more concentrated the acid will seem like.

 

[Ekman]

If there pipette is leaking the amount of H2SO4 decreases therefore less of the standard is required to titrate it. If less is required to titrate it, it must be less concentration ? im pretty sure our teachers right

The pipette contained the Na2CO3, not the sulphuric acid. So the amount of Na2CO3 would decrease not the H2SO4. We use less of the H2SO4 in the titration process, which results in it being at a higher concentration

EDIT: Check out q28 from the 2013 HSC exam, it has exactly the same premise, but instead of leaking, the standard isn't filled properly to the graduation line, which in essence means there is less standard being pipetted.

 

[InteGrand]

If there pipette is leaking the amount of H2SO4 decreases therefore less of the standard is required to titrate it. If less is required to titrate it, it must be less concentration ? im pretty sure our teachers right

Wasn't the base inside the pipette?

 

[Librah]

If there pipette is leaking the amount of H2SO4 decreases therefore less of the standard is required to titrate it. If less is required to titrate it, it must be less concentration ? im pretty sure our teachers right

The acid is in the burette according to Ekman

 

[InteGrand]

Also one question, can we assume that the number of moles is constant as the student did not realize it was leaking till after the experiment, so if we use the formula:



We basically prove it mathematically, as less volume is needed, more concentrated the acid will seem like.

But we need to be careful here. In our case, (which is the v that is changing due to spillage).

 

[Ekman]

It was a reverse titration experiment, so the unknown acid was in the burette, and the standard was pipetted into the conical flask.

 

[InteGrand]

The pipette contained the Na2CO3, not the sulphuric acid. So the amount of Na2CO3 would decrease not the H2SO4. We use less of the H2SO4 in the titration process, which results in it being at a higher concentration

EDIT: Check out q28 from the 2013 HSC exam, it has exactly the same premise, but instead of leaking, the standard isn't filled properly to the graduation line, which in essence means there is less standard being pipetted.

It doesn't ACTUALLY have a higher concentration of course, it's actually that the calculated value for the concentration assuming will be greater than the true value, because and . This formula doesn't seem relevant for this problem.

 

[Librah]

The premise of the question is a bit silly though, the 1st titration should always be a rough one, then a few more accurate ones to get more reliable results. Does the student realize that his pipette is leaking on the 1st then forgets, then does the 2nd with the same faulty pipette? Don't know if you can call this a titration.

 

[Ekman]

It doesn't ACTUALLY have a higher concentration of course, it's actually that the calculated value for the concentration assuming will be greater than the true value, because and . This formula doesn't seem relevant for this problem.

Of course, its just what is perceived and what is true. It is perceived to have a higher concentration (for example having a concentration of 5 mol/L), when the true concentration is 4 mol/L

 

[Drsoccerball]

i thought the H2SO4 was in the pipette...

 

[Librah]

i thought the H2SO4 was in the pipette...

GG pray4Drsock.

 

[PotatoAlpha]

my teacher claims that it would be decrease, because apparently in the formula c=n/v, the volume remains constant

But its LEAKING... How is it even possible for that not to change the volume??

 

[Ekman]

But its LEAKING... How is it even possible for that not to change the volume??

There is a difference between what is perceived and what is reality. It is perceived to have no change in volume but in reality, there is a change in volume. The question stated that the student realized the leaking after the titration.