And the ratio of the Thiosulfate to the Iodine is 1:2
Therefore, the ratio of the Thiosulfate to KIO3 is 6:1
In order to find moles of Thiosulfate, one must multiply the moles of KIO3(found earlier) by 6
= 0.00005 moles × 6
= 0.0003 moles of Thiosulfate
In order to find the concentration of Thiosulfate, one must divide the number of moles by the volume from the average titre
M = n/v
M = 0.0003 moles/ 0.01525 dm3
M = 0.019672131 mol dm-3
The following table shows values from part two of the calculations which are for determining the oxidizing power of bleach.
Average Titre value= (20.00 + 20.10)/2 = 20.05 cm3 = 0.02005 dm3
Uncertainty Propagation found later
The following table shows values for the mass taken each trial
Average Mass = (3.02 + 3.00)/2 = 3.01 g
Uncertainty Propagation Found Later
In order to calculate the Thiosulfate moles, one must multiply the concentration of Thiosulfate (calculated earlier) with the titre average because n = Mv
N = 0.019672131 mol dm-3 × 0.02005 dm3
N = 0.000403279 moles
Now, in order to find the moles of the Hypochlorite, one must look at the following two equations.
2 S203 2- (aq) + I2 (aq) 2 I- (aq) + S406 2- (aq)
ClO- + 2I- + 2H+ H2O + I2 + Cl-
The Hypochlorite to Iodine ratio is 1:1
And the Thiosulfate ratio to Iodine is 2:1
Therefore the Thiosulfate to Hypochlorite ratio is 2:1
Therefore, Hypochlorite moles = Thiosulfate moles/2
= 0.000403279 moles/2 = 0.000201639 moles
Since there was a dilution of 1 to 10, the moles above need to be multiplied by 10
= 0.000201639 moles × 10 = 0.00201639 moles
In order find the % by mass of the Hypochlorite, one needs to multiply the moles by (Molar mass of NaClO/mass average (Experimental)
= 0.00201639 moles × (74.5/3.01)
= 0.04990741245 × 100
= 4.990741245%
Uncertainty Propagation:
Uncertainty from massing scale = 0.02/3.01×100 = 0.66%
Uncertainty from Volumetric Pipette = 0.04/25×100 = 0.16%
Uncertainty from titration 1(Burette) = 0.05/15.25×100 = 0.33%
Uncertainty from titration 2(Burette) = 0.05/20.05×100 = 0.25%
Once of all of them have been added up,
= 0.66 + 0.16 + 0.33 + 0.25 = 1.4%
For relative uncertainty, 1.4% of 4.990741245% = 0.06987037743 %
Conclusion and Evaluation:
The experimental value obtained for the % by mass of the NaClO which is the oxidizing agent is 4.99%. The theoretical value which was given on the container of the bleach was 5.25%. Therefore, the percent error of this experiment is 4.94% showing that this was a fairly accurate result as the value for the percent error is not very high. However, if one looks at the error of 0.07% obtained in the experiment, one can notice that this error does not help the answer of 4.99% reach the value of 5.25% showing that the experimental data is not within the boundaries to reach an accurate answer. This is due to the few design, human and instrumental errors which are listed below.
Design Errors
Human Error
Instrumental Error
An overall improvement method to reduce random errors in this lab would be repetition of trials. Overall, this experiment was fairly accurate and precise resulting in not many errors overall.
