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# Some general queries, calculating concentration. Watch

1. In one of our labs we was doing titration using Vinegar (acetic acid solution), sodium hydroxide (aqueous solution) NaOH and Phenolphthalein.

Adding the Phenolphthalein to 20ml of vinegar then using a burette to add NaOH until the vinegar solution goes a solid pink colour.

We was given a worksheet to complete on the lab, but to me some bits don't make alot of sense, our lecturer isn't English and there is somewhat of a language barrier there making it hard for us students to understand her and her to understand us.

Firstly we had to fill in a table.

The burettes were 50ml and our lecturer reckons that the first column which states "initial volume of NaOH solution in burette (ml)" should be 0ml.

1. Shouldn't the initial volume be 50ml as thats how much NaOH was added to the burette before being dripped into the vinegar below??

Lecturer also said that the column which states "final volume of NaOH solution in burette (ml)" should hold the same value as the final column "volume of NaOH solution that reacted in ml"

2. Why are these the same, surely thats wrong? For example on one of my 'runs' the final volume in the 50ml burette was 27.2ml. Which means that 22.8ml had enter the flask at the bottom with the vinegar and thus that is the amount reacted?

Yet the lecturer states that if there is 27.2ml left in the burette, then it is 27.2ml which has reacted? Surely thats wrong, how could that 27.2ml of NaOH of reacted if it was still in the burette and only 22.8 had entered the flask and reacted with the vinegar and phenolphthalein solution.

I do require some help with calculating concentration but I'd like to clear these points up first. Thanks.
In one of our labs we was doing titration using Vinegar (acetic acid solution), sodium hydroxide (aqueous solution) NaOH and Phenolphthalein.

Adding the Phenolphthalein to 20ml of vinegar then using a burette to add NaOH until the vinegar solution goes a solid pink colour.

We was given a worksheet to complete on the lab, but to me some bits don't make alot of sense, our lecturer isn't English and there is somewhat of a language barrier there making it hard for us students to understand her and her to understand us.

Firstly we had to fill in a table.

The burettes were 50ml and our lecturer reckons that the first column which states "initial volume of NaOH solution in burette (ml)" should be 0ml.

1. Shouldn't the initial volume be 50ml as thats how much NaOH was added to the burette before being dripped into the vinegar below??

Lecturer also said that the column which states "final volume of NaOH solution in burette (ml)" should hold the same value as the final column "volume of NaOH solution that reacted in ml"

2. Why are these the same, surely thats wrong? For example on one of my 'runs' the final volume in the 50ml burette was 27.2ml. Which means that 22.8ml had enter the flask at the bottom with the vinegar and thus that is the amount reacted?

Yet the lecturer states that if there is 27.2ml left in the burette, then it is 27.2ml which has reacted? Surely thats wrong, how could that 27.2ml of NaOH of reacted if it was still in the burette and only 22.8 had entered the flask and reacted with the vinegar and phenolphthalein solution.

I do require some help with calculating concentration but I'd like to clear these points up first. Thanks.
The initial volume is zero (at least for the first reading) this is because if you read the burette it says zero.
Once again for the second question - the volume reacted is the volume difference. If the initial reading was zero then the volume difference is as your lecturer says.
3. (Original post by joostan)
The initial volume is zero (at least for the first reading) this is because if you read the burette it says zero.
Once again for the second question - the volume reacted is the volume difference. If the initial reading was zero then the volume difference is as your lecturer says.

Ok thanks that makes sense that its from the initial reading on the burette is the zero point not the 50ml volume.

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Updated: March 26, 2013
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