Analysis of a Commercial Bleach Lab Guidelines

Name, Exp. Name, Number, Date (we did lab), Partner(s) Purpose Compound Names, Formulas, and Molar Masses (5 used – no formula or molar mass for

starch) Reactions (use the four listed on the front page of the lab) Procedure/Observations

Include initial observations and final observations/odors, masses of KI… Results (Data Table)

Make a table that has your data of KI masses, and the three volumes (from the three trials) needed to titrate the bleach

Calculations (Data and Calculations Section in lab)1. Use the equations given on the front page to determine the number of moles of

sodium thiosulfate that are equivalent to one mole of sodium hypochlorite.2. From your three trials, calculate the average volume of Na2S2O3 needed for the

titration of 25.00mL of diluted bleach.3. Use the average volume and the molarity of Na2S2O3 to determine the molarity of

the diluted bleach. (Find moles of Na2S2O3, convert to moles of NaClO, and divide by volume of dilute bleach that was titrated in each trial to get M).

4. Calculate the molarity of the commercial bleach (not diluted) using your answer from step 3 and the M1V1 = M2V2 equation. (Use volume of concentrated bleach and total volume of dilute bleach)

5. Assume that the density of the commercial bleach is 1.08g/mL. Calculate the percent by mass of NaClO in the commercial bleach. (Start with molarity of concentrated NaClO found in part 4. Determine the molarity per mL instead of liter. Next, divide by the density (you’ll have a label of mole/g at this point). Then multiply this by the molar mass of NaClO which has a label of g/mol so all labels cancel. Finally multiply by 100 to get a percent!)

6. The label on the commercial bleach reports the percent by mass NaClO to be 6.0%. Calculate the percent error of your value, assuming that the label value is correct.

7. Calculate the average deviation of the three values you obtained for the volume of Na2S2O3 solution.

a) Take each of your three volumes and subtract it from your average volume. If it is neg., take the absolute value. (You’ll have three answers)1. Ex: Trial 1: Volume added = 18.42mL

Avg. volume 18.36mL i. 18.36-18.42 = -.08 = .08

b) Average deviation is found by adding the values obtained in step a and dividing by the number of trials (3).

c) Find the relative deviation by taking your answer from step b and divide it by your avg. volume, multiply by 100 to get a percent. (This is how much your answers deviate from your average volume.)

Diagram (Draw setup of buret and titration) Remember to label!!!

Conclusions and Error Analysis Discussion of Theory

Explain the oxidation-reduction titration including the chemistry and math behind it that enabled us to find the amount of hypochlorite ion present in the bleach.

Post-Lab Questions (Discussion Questions in lab handout)- SKIP QUESTIONS 2 & 7