Quantitative Analysis of Sodium Hypochlorite in Commercial Bleach: Titration and Concentration Determination

Commercial bleach, a commonly used household product, is a solution of sodium hypochlorite (NaClO). In this laboratory analysis, we will delve into the composition of commercial bleach, conduct various calculations, and explore its practical applications.

The primary active ingredient in commercial bleach is sodium hypochlorite, which is a powerful oxidizing agent. The chemical formula for sodium hypochlorite is NaClO. It is crucial to determine the concentration of sodium hypochlorite in the commercial bleach solution for various applications, such as disinfection and laundry.

Calculations:

1. Determining Concentration:
   • The concentration of sodium hypochlorite in bleach is typically expressed as a percentage. The formula to calculate concentration is: Concentration (%)=(Volume of NaClOTotal Volume of Solution)×100Concentration (%)=(Total Volume of SolutionVolume of NaClO​)×100
2. Molarity Calculation:
   • Molarity (M) is another unit for expressing concentration. It is calculated using the formula: Molarity (M)=Moles of SoluteLiters of SolutionMolarity (M)=Liters of SolutionMoles of Solute​
   • The molar mass of sodium hypochlorite is crucial for this calculation, which can be determined by adding the atomic masses of sodium, chlorine, and oxygen.
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Experimental Procedure:

1. Titration:
   • Titration is a widely used technique to determine the concentration of a substance in a solution. In this case, it can be employed to find the concentration of sodium hypochlorite in the commercial bleach.
2. Preparation of Standard Solution:
   • A standard solution of a known concentration of sodium thiosulfate can be prepared and used as a titrant. The balanced chemical equation for the reaction between sodium thiosulfate and sodium hypochlorite is essential for calculations.
3. Titration Process:
   • The titration involves adding the sodium thiosulfate solution to the bleach until the reaction is complete, indicated by a color change.
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     The volume and concentration of the titrant are recorded.

Results and Analysis:

1. Concentration of Sodium Hypochlorite:
   • The concentration of sodium hypochlorite in the commercial bleach can be determined using the titration results and the appropriate formulas. This information is crucial for consumers and industries relying on bleach for various purposes.
2. Molarity Calculation:
   • With the concentration known, the molarity of the commercial bleach can be calculated, providing a more standardized measure for its potency.

Applications:

1. Disinfection:
   • Understanding the concentration of sodium hypochlorite is crucial for effective disinfection. Different applications, such as water treatment and surface sanitation, require specific concentrations for optimal results.
2. Laundry:
   • In laundry, bleach serves as a stain remover and a whitening agent. Knowing the concentration aids in determining the appropriate amount to use without damaging fabrics.

In this laboratory analysis, we have explored the composition of commercial bleach, conducted calculations to determine its concentration and molarity, and discussed practical applications. Understanding the chemistry behind commercial bleach is essential for its safe and effective use in various settings. By employing titration techniques and relevant formulas, we can quantify and analyze the potency of this commonly used household product.

Materials and Chemicals:

• Commercial Bleach, NaClO
• Hydrochloric Acid, HCl, 3M, 6 mL
• Potassium Iodide, KI, 6 g
• Sodium Thiosulfate Solution, Na2S2O3, 0.100 M, 70 mL
• Starch Solution, 2%, 3 mL

Materials and Equipment:

• Balance, 0.1-g precision
• Buret, Buret Clamp
• Erlenmeyer Flask
• Pipet Bulb
• Ring Stand
• Transfer Pipets
• Volumetric Flask with Stopper
• Wash Bottle
• Distilled Water
• Weighing Dish

Experimental Procedure:

1. Measure 5.00 mL of commercial bleach into a 100-mL volumetric flask.
2. Dilute the bleach with distilled or deionized water to the mark and mix thoroughly.
3. Weigh 2 g of solid KI. Pipet 25.0 mL of the dilute bleach into an Erlenmeyer flask.
4. Add solid KI and 25 mL of distilled or deionized water.
5. Add 2 mL of 3 M HCl while stirring the solution.
6. Fill the buret with 0.100 M sodium thiosulfate solution until the iodine color fades to light yellow.
7. Add one dropperful of starch solution.
8. Continue the titration until one final drop of Na2S2O3 causes the color to disappear.
9. Record the final buret reading.
10. Repeat the titration procedure two more times for accuracy.

Analysis and Calculations:

• Use the titration results to calculate the concentration of sodium hypochlorite in the commercial bleach.
• Utilize stoichiometry to relate the amount of sodium thiosulfate used to the amount of sodium hypochlorite present.
• Consider repetitions of the titration for precision and reliability of the results.

This experiment provides a practical approach to determine the concentration of sodium hypochlorite in commercial bleach, essential for understanding its effectiveness in various applications. The titration technique, coupled with chemical reactions and calculations, forms a comprehensive method for quantitative analysis.

Data Collection

Calculations:

1. Determine the number of moles of sodium thiosulfate equivalent to one mole of sodium hypochlorite: The calculation involves a series of conversions, resulting in the equivalence of 1 mol ClO- to 2 mol S2O32-.
2. Calculate the average volume of Na2S2O3 for titration of 25.0 mL of diluted bleach: The average volume is obtained by adding three values, resulting in 18.33 mL.
3. Use average volume and molarity of Na2S2O3 to find the molarity of diluted bleach: By applying the formula, the molarity of the diluted bleach is determined as 0.037 M ClO-.
4. Calculate the average molarity of commercial bleach before dilution: The calculation yields a molarity of 0.73 M ClO- before dilution.
5. Determine the average percent by mass of NaClO in commercial bleach: Using the density and molarity, the percent by mass is calculated as 5.03%.
6. Calculate the average deviation of the three values: The absolute differences are summed and averaged, resulting in an average deviation of 0.89.
7. Calculate the percent error: The percent error is determined to be 16.2%.

Questions:

1. Define oxidation and reduction: Oxidation involves the gain of oxygen, while reduction involves the loss of oxygen.
2. Write balanced oxidation and reduction half-reactions for the overall redox reactions in equations (1) and (3): Equation 1 involves the reduction of chlorine and oxidation of hydroxide, while Equation 3 involves the reduction of iodine.
3. In this analysis, why is an aliquot of the initial solution diluted? Dilution improves accuracy during titration.
4. How many 25.0-mL aliquots can be measured from a 100-mL volumetric flask? Only 3 complete aliquots can be obtained due to practical limitations in removing all liquid.
5. Calculate the oxidation number of sulfur in S4O62-: The oxidation number is 5/2, and sulfur atoms in S4O62- have different oxidation numbers (5 and 2).
6. How would laboratory mistakes affect the calculated percent of NaClO? Various mistakes could result in a higher, lower, or unchanged value.
7. What is the major source of experimental error in this experiment? Over-titrating is identified as a major source of error.

The experiment determined sodium hypochlorite in commercial bleach through precise titration. Dilution enhanced accuracy, and starch acted as a color indicator. Starch was added late to avoid irreversible reactions. The results were consistent, possibly due to dilution.

Sources of error included over-titrating and prematurely adding starch. Over-titration could lead to inaccurate percent NaClO. The error calculation resulted in a 16.2% error.

The experiment successfully determined sodium hypochlorite in commercial bleach through precise titration. Dilution contributed to result consistency, and starch served as a late-stage color indicator. Identified error sources included over-titrating and premature starch addition, potentially affecting the accuracy of percent NaClO determination. The overall process was characterized by attention to detail and methodical execution.