Problem: What is the percentage composition by mass of NaClO in the bleach product?Express your answer to three significant figures and include the appropriate units.Analysis of bleach involves two sequential redox reactions: First, bleach is reacted in acid solution with excess iodide anion to produce yellow-colored iodine:ClO− + 2 H+ + 2 I− → I2 + Cl− + H2OThen, to determine how much of the iodine was formed, the solution is titrated with sodium thiosulfate solution:I2 + 2 S2O32− → 2 I− + S4O62− A bit of starch is added to the titration reaction. Starch is intensely blue in the presence of I2. The solution thus turns from deep blue to colorless at the reaction equivalence point.A sample of a new cleaning product, "Joe's Famous Bleach Cleaner," with a mass of 48.0 g, was diluted with an acetic acid solution containing excess I−. A small amount of starch indicator solution was then added, turning the solution a deep bluish-purple. The solution was then titrated with 0.450 M sodium thiosulfate, Na2S2O3, containing the ion S2O32−. A volume of 39.0 mL of sodium thiosulfate, the titrant, was needed to turn the solution colorless.Percent compositionTo obtain percent composition by mass, use the equation given here:percent composition=mass due to specific componenttotal mass of mixture×100%

FREE Expert Solution
87% (46 ratings)
Problem Details

What is the percentage composition by mass of NaClO in the bleach product?

Express your answer to three significant figures and include the appropriate units.


Analysis of bleach involves two sequential redox reactions: First, bleach is reacted in acid solution with excess iodide anion to produce yellow-colored iodine:

ClO + 2 H+ + 2 I → I2 + Cl + H2O

Then, to determine how much of the iodine was formed, the solution is titrated with sodium thiosulfate solution:

I2 + 2 S2O32− → 2 I + S4O62− 

A bit of starch is added to the titration reaction. Starch is intensely blue in the presence of I2. The solution thus turns from deep blue to colorless at the reaction equivalence point.


A sample of a new cleaning product, "Joe's Famous Bleach Cleaner," with a mass of 48.0 g, was diluted with an acetic acid solution containing excess I. A small amount of starch indicator solution was then added, turning the solution a deep bluish-purple. The solution was then titrated with 0.450 M sodium thiosulfate, Na2S2O3, containing the ion S2O32−. A volume of 39.0 mL of sodium thiosulfate, the titrant, was needed to turn the solution colorless.

Percent composition

To obtain percent composition by mass, use the equation given here:

percent composition=mass due to specific componenttotal mass of mixture×100%

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Solution Stoichiometry concept. You can view video lessons to learn Solution Stoichiometry. Or if you need more Solution Stoichiometry practice, you can also practice Solution Stoichiometry practice problems.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Michaels' class at IRSC.