Backwards Titration

[hamman]

I recently did a backwards titration...

Instead of adding base to acid and indicator, I added acid to base and indicator. The unusual thing was that more of the acid was used than base.

 

Eg. The same titration was carried out normally, add base to acid-indicator,

and I get oh 25 cm cube of base used to change indicator color. Now I reverse things around and add acid to base-indicator and get 45 cm cube of acid used!

 

I was assuming on the same volume readings either way:confused:

[RyanJ]

I recently did a backwards titration...

Instead of adding base to acid and indicator' date=' I added acid to base and indicator. The unusual thing was that more of the acid was used than base.

 

Eg. The same titration was carried out normally, add base to acid-indicator,

and I get oh 25 cm cube of base used to change indicator color. Now I reverse things around and add acid to base-indicator and get 45 cm cube of acid used!

 

I was assuming on the same volume readings either way:confused:[/quote']

 

Did you repeat the experimen, could there have been a mistake in your experiment?

 

If it was a mistake, it happens all the time (Especailly too me ).

 

I suggest you do each experiment 3 times and then use the average results, they are normally more accurate, if you still get the same answer I have no idea why!

 

Cheers,

 

Ryan Jones

[hamman]

did it 8 times in a 16-well!!! no errors, im sure!

[akcapr]

what indicator did you use

[Tetrahedrite]

You simply need to think a little more laterally, your results indicate that the concentration of the acid is lower than that of the base.

 

What size aliquot did you use for each titration?

 

The only time you will get an exactly equal volume of titrant for both the acid and the base is when there is a 1:1 molar ratio (concentration) of these components.

[hamman]

Thanks Tetrahedrite. That must be it!