# Calculate the % w/v NaOCl in the sample of bleach ??

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A 24.90-mL sample of liquid bleach (contains NaOCl; 74.44 g/mol) was diluted to 1000.0 mL in a volumetric flask. A 25.00-mL aliquot of the diluted sample was transferred into an Erlenmeyer flask and treated with excess KI to oxidize the OCl- to Cl2 and producing I2. The liberated I2 was determined by titrating with 0.0458 M Na2S2O3 and required 16.23 mL to reach a starch indicator endpoint.

Calculate the % w/v NaOCl in the sample of bleach. Give your answer to 2 places after the decimal point.

Reactions: 2OCl– + 2I– + 4H+ → I2 + Cl2 + 2H2O

```
I2 + 2S2O32– → 2I– + S4O62–
```

HINT: This is an example of an Iodometric method of analysis (slides 29 - 30 of Module 5 Lecture Notes). Iodometric methods are indirect titrimetric methods that require the use of standardized thiosulfate solutions. They do not involve a back-titration. In any indirect method of analysis, the key is to derive the overall stoichiometry between the analyte (in this case NaOCl) and the standard solution (in this case thiosulfate). Remember: the final answer must be expressed as % w/v NaOCl, not as % w/v OCl–.

A 24.90-mL sample of liquid bleach (contains NaOCl; 74.44 g/mol) was diluted to 1000.0 mL in a volumetric flask. A 25.00-mL aliquot of the diluted sample was transferred into an Erlenmeyer flask and treated with excess KI to oxidize the OCl- to Cl2 and producing I2. The liberated I2 was determined by titrating with 0.0458 M Na2S2O3 and required 16.23 mL to reach a starch indicator endpoint.

Calculate the % w/v NaOCl in the sample of bleach. Give your answer to 2 places after the decimal point.

Reactions: 2OCl– + 2I– + 4H+ → I2 + Cl2 + 2H2O

```
I2 + 2S2O32– → 2I– + S4O62–
```

HINT: This is an example of an Iodometric method of analysis (slides 29 - 30 of Module 5 Lecture Notes). Iodometric methods are indirect titrimetric methods that require the use of standardized thiosulfate solutions. They do not involve a back-titration. In any indirect method of analysis, the key is to derive the overall stoichiometry between the analyte (in this case NaOCl) and the standard solution (in this case thiosulfate). Remember: the final answer must be expressed as % w/v NaOCl, not as % w/v OCl–.

##### 1 Answer

#### Explanation:

Thus

The hypochlorite solution, therefore, has the mass concentration (in grams per milliliter)