A student followed the procedure of this experiment to determine the percent NaO

Question

A student followed the procedure of this experiment to determine the percent NaOCl in a commercial bleaching solution that was found in the basement of an abandoned house. The student diluted 50.00 mL of commercial bleaching solution to 250 mL in a volumetric flask, and titrated a 20-mL aliquot of the diluted bleaching solution. The titration required 35.46 mL of 0.1052M Na2S2O3 solution. A faded price label on the gallon bottle read $0.79. The density of the bleaching solution was 1.10 g/mL

Calculate the number of moles of OCl-- ion required for the titration

Explanation / Answer

This reaction must be carried out in a basic solution - It is necessary to add NaOH to the solution before titration.
Equation:
4 NaOCl + Na2S2O3 + 2 NaOH 4 NaCl + 2 Na2SO4 + H2O
4mol NaOCl react with 1 mol Na2S2O3

Calculate the number of mol Na2S2O3:
Mol Na2S2O3 in 35.46mL of 0.1052M solution = 0.0354*0.1052 = 0.00373 mol Na2S2O3 used in the titration.

then the number of moles of OCl-- ion required for the titration = 0.00373*4 = 0.015 moles

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