Final Chemistry Lab Report

Topics: Chlorine, Iodine, Concentration Pages: 4 (817 words) Published: September 8, 2013

The overall objective of this experiment is to determine the mass percent of NaClO, sodium chloride, in standard bleach. The purpose of part 1, is to standardize Sodium Thisulfate, Na2S2O3, with the primary standard Potassium Iodate, KIO3. The standardized Na2S2O3 will then be used in Part 2, to help determine the mass percentage of sodium chloride in bleach. The chemical equation used in standardizing sodium thisulfate is, IO3- (aq) + 5I- (aq) + 6H+(aq) ---> 3I2 + 3H2O followed by I2 (aq) + 2 S2O3-2 (aq) ---> 2I- (aq) + S4O6-2 (aq). This reaction shows that when KIO3 and KI are combined under high acidity, I- is oxidized by IO3- and forms I2. Once sodium thisulfate is added to the mixture, I2 is reduced to I-, once again. Once all of the iodide is used up in the reaction, the liquid will changed from brown/yellow to clear. This means that the solution has reached an equivalence point. Since I2 changes the color of the solution, it will be used as an indicator in the titration experiment. In part 2 of the experiment, Na2S2O3 is used to determine the mass percent of NaClO in bleach. The reaction related to this part is as follows: ClO- (aq) + 2I- (aq) + 2H+ ---> I2 (aq) + Cl- (aq) + H2O and I2 (aq) + 2S2O3-2 (aq) ---> 2I- (aq) + S4O6-2 (aq). KI is added to dilute bleach in which the hypochlorite will reduce I- to form I2. Once this solution is created, it will be titrated with the sodium thisulfate solution from part 1 to find the mass percent of sodium hypochlorite in the bleach samples.



Part 1

Trials | Eq Point: Na2S2O3 added |
1 | 22.50 mL |
2 | 22.60 mL |
3 | 23.00 mL |

Part 2

Trials | Eq Point: Na2S2O3 added |
1 | 29.10 mL |
2 | 28.70 mL |
3 | 29.30 mL |

Average: 29.0 mL of Na2S2O3


In part 1...

References: University of Kansas – Chemistry 184, Spring 2012
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