Chem help (1 Viewer)

[Mowhuss]

This is a question that comes up every now and then and takes me too long to wrap my head around. Could someone please help me out with this question.

 

[ColdMint123]

So theres two errors in the process.
Step i. we rinse the burette with the solution going in it so that the solution does not get diluted. Since the person rinsed the burette with water, acid gets diluted. So we have a lower concentration of acid then what we have noted.

Step iii. The conical flask is rinsed with base solution which is wrong because now we add more moles of the base solution which has not been accounted for.

So essentially, you are titrating a weaker acid with a more moles of base, which means we are going to need a much larger volume of acid to reach endpoint. A larger volume of acid means we calculate the moles of base to be much higher. Which means the concentration of base will be higher. So C.

hopefully that makes sense, feel free to correct me if there is an error in my thought process

 

[icycledough]

Seems about right, unless one of the Chem moderators find something else. Honestly though, I used to hate these questions as well, as I would have to go through each step and think about how concentration or moles will be affected in each step; but the best way to go about it is to do what Coldmint123 did, to take each step logically, one at a time, and write down the change.

 

[CM_Tutor]

So theres two errors in the process.
Step i. we rinse the burette with the solution going in it so that the solution does not get diluted. Since the person rinsed the burette with water, acid gets diluted. So we have a lower concentration of acid then what we have noted.

Step iii. The conical flask is rinsed with base solution which is wrong because now we add more moles of the base solution which has not been accounted for.

So essentially, you are titrating a weaker acid with a more moles of base, which means we are going to need a much larger volume of acid to reach endpoint. A larger volume of acid means we calculate the moles of base to be much higher. Which means the concentration of base will be higher. So C.

hopefully that makes sense, feel free to correct me if there is an error in my thought process

This is correct, except for in one way that everyone should be careful about, and I've highlighted it in bold. It is correct that the acid has been diluted, so you are titrating with a lower concentration of acid, but its nature / strength is unchanged. You are titrating with a smaller quantity of acid, not with a weaker acid.

Be careful on terminology: more dilute does not mean weaker, more concentrated does not mean stronger.

 

[ColdMint123]

This is correct, except for in one way that everyone should be careful about, and I've highlighted it in bold. It is correct that the acid has been diluted, so you are titrating with a lower concentration of acid, but its nature / strength is unchanged. You are titrating with a smaller quantity of acid, not with a weaker acid.

Be careful on terminology: more dilute does not mean weaker, more concentrated does not mean stronger.

Yep makes sense, I should have said "A more diluted acid" right?

 

[CM_Tutor]

Yep makes sense, I should have said "A more diluted acid" right?

Yes... you were wrong in the sense of carelessly used terminology. I doubt you actually thought / meant "weaker" but it is a common misconception so I feel the need to jump on it when I see it.