Volumetric analysis
exercise 4 solution
|
Volume
|
Volume
|
Volume
|
|
| Start |
11.40
mls
|
21.43
mls
|
13.40
mls
|
| Finish |
22.22
mls
|
32.22
mls
|
22.22
mls
|
| Total |
10.82
mls
|
10.79
mls
|
8.82
mls
|
Average titre = (10.82
+ 10.79)/2=10.81mls
To calculate the average
titre take only the concordant results
Irene determines the amount of vitamin C in a sample of fruit juice. A 25.00ml sample of the juice is diluted to 250ml in a volumetric flask. A 20.00 ml aliquot was taken and titrated against an 0.023M standard iodine solution. Three titres were obtained and the results are shown on the left. What is the concentration of vitamin C in the original fruit juice?
Click to see a simple animation of the procedure that may help you visualise the process.
The equation for the reaction is shown below.
Step 1 Calculate
the mole of substance delivered from the burette. In this case iodine
solution
Mole = Average Volume(litres)
X Concentration
Mole = 0.011 X 0.023 = 0.000253
Step 2 Using
the equation calculate the number of mole of substance in the 20 ml
aliquot. In this case vitamin C.
For every one mole of
iodine one mole of vitamin C reacts. Hence the number of mole of vitamin
C present is 0.000253. The number of mole of vitamin C present in the
250ml flask can be calculated by 0.000253(250/20)
= 0.00032
Step 3 Find the concentration of the substance in theoriginal fruit juice. In this case find the concentration of vitamin C in the 25 ml sample of fruit juice.
The Concentration in the 25ml sample of fruit juice
= 0.00032/0.025 = 0.0126