The ideal titration volume is between 35 and 50 mL since this uses most of the v

Question

The ideal titration volume is between 35 and 50 mL since this uses most of the volume of a 50 mL

buret without going over. Achieving a larger titration volume (35 mL to 50 mL) instead of a small

titration volume (say 10 mL) reduces contributions of small errors such as misreading a buret.

An experiment to verify the hypochlorous acid content in a commercial brand of bleach requires

titration of a certain volume of bleach with a solution of iodide.

HOCl(aq) + H+(aq) + 3I (aq) I3^(aq) + Cl(aq) + H2O(l)

a) If the manufacturer states that the bleach is 5.5% HOCl by volume, what volume of bleach

sample should be titrated with 1.525 M sodium iodide solution to provide an acceptable

titration volume at the equivalence point? You may require additional data which can be

accessed through online sources or the CRC handbook (give references).

b) How would you dispense this particular volume? (what type of glassware would you use?)

Briefly explain.

Explanation / Answer

I will first calculate the Molarity of HOCl of the bleach. Knowing that the 5,5% v/v and the density is 1.084 g/mL:

5.5 % v/v means that we have 5 mL in 100 mL, or even 50 mL in 1000 mL,

Then, in 1 mL we have 1.084 g, or even 1000 mL we have 1084 g,

The molecular weight of HOCl:

MM = 1 + 16 + 35.5 = 52.5 g/mol

then mol of HOCl = 1084 / 52.5 = 20.65 moles

M = 20.65 / 50 = 0.412 M

Then, the concentration of HOCl is 0.412 M.

Now, we use the following expression: M1V1 = M2V2

so, we have the concentration of both reactants, and the volume required, so:

0.412V1 = 1.525 x 35

V1 = 130 mL

This volume, I'll put in an erlenmeyer flask of 150 mL. To do this, first, I'll add the bleach in a beaker of 150 mL, then, I'll use a volumetric pipet of 100 mL and another of 30 mL. Then, I'll add the bleach in the erlenmeyer flask with these two aditions.

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