Confused on the working out of this question (1 Viewer)

[Dane Red]

The part that confuses me is where it states that the amount of citric acid in 75mL as there doesn't seem to be any calculations for it.

 

[Eagle Mum]

The question states in ‘Step 2: A 75.00 mL bottle of drink was opened’. Distilled water was added in step three for the second titration but the only citric acid present came from the bottle of drink and so after working out the total number of moles (in the 250 mL beaker of diluted solution), this total amount should be divided by the volume of the original bottle of drink (ie. 75 mL) in order to determine the concentration in the original soft drink.

 

[Dane Red]

The question states in ‘Step 2: A 75.00 mL bottle of drink was opened’. Distilled water was added in step three for the second titration but the only citric acid present came from the bottle of drink and so after working out the total number of moles (in the 250 mL beaker of diluted solution), this total amount should be divided by the volume of the original bottle of drink (ie. 75 mL) in order to determine the concentration in the original soft drink.

The question is that why is the moles in 250mL the same in 75mL. Shouldn't the moles change after you go to the 75ml bottle?

 

[Eagle Mum]

The question is that why is the moles in 250mL the same in 75mL. Shouldn't the moles change after you go to the 75ml bottle?

All of the citric acid in the experiment system was originally contained in the 75mL of bottled drink. Water was added to make the solution a total volume of 250mL - in other words, the citric acid concentration became more dilute in the titration solution compared to the drink but the total amount of it hadn't changed, between the drink and the solution.

The second titration only used 25mL of the diluted solution (ie. one tenth of the 250mL volume), so the amount that was determined, by titration, to be in 25mL (0.00097331791), had to be multiplied by ten to get the total amount in the 250mL solution which was all the citric acid in the original drink bottle of 75mL, so to determine the concentration in the original drink, the total amount in the solution should be divided by the original volume of the bottled drink.