Solved: Redox Titration Help - Calculate NaOCl Concentration

In summary, the conversation discusses a redox titration experiment involving a diluted bleach solution. The person is struggling to calculate the concentration of hypochlorite ions and the concentration of NaOCl in grams per liter. Using the equation OCL- + 2H+ + 2S2O3-2 = Cl- + S4O6-2 + H2O, they determine that 0.001823 mol of thiosulphate reacted with 0.0009115 mol of hypochlorite. Using proportion and the formula c=n/v, they calculate the concentration of hypochlorite to be 0.03646 mols per liter. To find the concentration in grams per liter, they
  • #1
Paulo2014
81
0
[SOLVED] Redox titration help

Hi
In class we are doing a redox titration with a diluted bleach solution. We made the aliquot with 5 ml of 10% KI solution and 5ml H2SO4 with 25 ml of the diluted bleach solution. And the burrette solution was sodium thiosulfate @ 0.1 mol L-1. my results were as follows... 18.2, 18.2 and 18.3



OCL- + 2H+ + 2S2O3-2 = Cl- + S4O6-2 +H2O



I know that the average volume used is 18.23. The question asks to calculate the concentration of hypochlorite ions in diluted bleach solution and to calculate the concentration of NaOCl in grams per liter. please could someone help from this point as I am completely stuck...
 
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  • #2
you equation says that 2 mol of thiosulphate reacts with 1 mol hypochlorite.

how many mols of thiosulphate was needed from burette? then, how many mols of hypochlorite was present in the solution? this amount of hypochlorite is found in what volume?

use proportion.
 
  • #3
How do you calculate moles again?
 
  • #4
your thiosulphate concentration is 0.1M. this implies that in 1000 ml you will have 0.1 mol of thiosulphate. how many mol of thiosulphate you will have in the average volume from the burette? use proportion.

now this amount of thiosulphate will react with hypochlorite. but according to the stoichiometric equation, 2 mol of thiosulphate reacts with 1 mol of hypochlorite.

can you find out how many mols of hypochlorite reacted with the number of mol of thiosulphate you just calculated above?
 
  • #5
I got that the number of moles of thiosulphate is 0.001823 mol. And because the equation is 2 mol thiosuphate for 1 mol hypochlorite so I divide by 2 to get that the number of moles of hypochlorite is 0.0009115. Is that right?
 
  • #6
yeah...

how you find the concentration of hypochlorite now?!
 
  • #7
c=n\v so concentration of hypochlorite will be 0.0009115 divided by 0.0250 which is 0.03646 mols per liter. Is that correct? what do I do from here to find the concentration in grams per liter?
 
  • #8
i think it's much easier to use proportion than formulae with these calculations. it's up to you though.

so, 25 ml of hypochlorite contains 0.0009115
1000 ml would contain _________ mol

what is the mass of 1 mol NaOCl? hint: Mr

and always give your answers in scientific notation. e.g 9.115 * 10^-4
 
  • #9
So does that mean that the mass of NaOCl in grams per liter would be the concentration times the relative molar mass?
 
  • #10
yeah... if the solution contains x mol per liter, the x mol also corresponds to a certain mass. then you have x*r.m.m. g/L
 

1. What is a redox titration?

A redox titration is a type of chemical analysis method used to determine the concentration of a substance, usually an oxidizing or reducing agent, in a solution. It involves a reaction between the substance being analyzed and a known substance called a titrant.

2. How is a redox titration performed?

A redox titration is performed by adding a titrant, which has a known concentration, to the substance being analyzed in a controlled manner until the reaction is complete. This is usually done by measuring the volume of titrant added and using an indicator to determine the endpoint of the reaction.

3. What is the purpose of calculating NaOCl concentration in a redox titration?

The purpose of calculating the concentration of NaOCl in a redox titration is to determine the amount of active chlorine present in a solution. This is important in various applications, such as water treatment, where the concentration of NaOCl is used to disinfect water.

4. What equipment is needed for a redox titration?

The equipment needed for a redox titration includes a burette, a pipette, a conical flask, a stirrer, an indicator, and a standardized solution of the titrant. Other common laboratory equipment such as a balance, beakers, and a wash bottle may also be used.

5. What factors can affect the accuracy of a redox titration?

The accuracy of a redox titration can be affected by several factors, such as the concentration of the titrant, the purity of the substances being used, the temperature and pH of the solution, and human error in measuring and recording data. It is important to carefully control these factors to ensure accurate results.

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