PRE LAB QUESTIONS 1.)A 10-mL pipet wasused to deliver a sample of commercial ble

Question

PRE LAB QUESTIONS

1.)A 10-mL pipet wasused to deliver a sample of commercial bleach to a 100-mLvolumetric flask. Distilled water was added and the flask was inverted several times to produce a uniform, 100.00-mL sample ofdiluted bleach. The pipet was rinsed with diluted bleach and thenused to deliver 10.00-mL of diluted bleach to an Erlenmeyer flask.Sufficient quantities of H2SO4 and KIwere added to convert all OCl- ions to Cl- ions, with consequent conversion of some iodideions to I3-ions. The 10.00 mL of diluted bleach requiredthe addition of 24.76 mL of 0.0537 M thiosulfate for complete reaction. Use this data to compute the molarity of the undiluted bleach with respect to sodium hypochlorite.

Explanation / Answer

The reaction of iodine with hypo is

I2 + 2S2O3-2 --> 2I- + S4O6-2

The I3- that is mentioned is a complex of I2 and I- (the unreacted portion of it), so it is interchangeable quantity-wise. We dissolve Iodine in water by converting it into I3-.

Now lets equate the equivlaence

We can calculate the mole of thiosulphat by multiplying the volume with moalrity
0.02476 L X 0.0537M = 0.001329 moles,

which, from stoichiometry means half of these moles of I2/I3- will react which is
0.000664 moles.
The balanced reaction between KI and OCl- has 1:1 stoichiometry I3- and Cl- in the products:

3I- + Cl+ ~> I3- + Cl-

so amount of OCl is equivalent to that of I3 found before: 0.000664 moles.

The concentration of this solution is 0.00064 moles/0.01000L = 0.0664 M.

As this solution was obtained from the original by duluting 10 times, the initial concentration of OCl- is 0.664 M.

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