Question

Suppose a student diluted and titrated a bleach unknown exactly as described in the experimenal procedure, except only a single titration was performed which required 12.02 ml of 0.100 M Na2S2O3.

The density of the original, undiluted bleach unknown was 1.040 g/ml.

1)Calculate the number of moles of Na2S2O3 used in the titration

2)Calculate the number of moles of ClO- in the sample titrated.

3)Calculate the grams of NaClO in the titrated bleach sample (assuming all the hypochlorite ion comes from sodium hypochlorite).

4)Calculate the mass in grams of undiluted bleach bleach that was in the sample of bleach titrated

5)Using the answers to question to 3 & 4 , calculate the weight percent of NaClO in the undiluted bleach.

Answer 1

(1) Moles of Na2S2O3 == 12.02 x 10^-3  x 0.100 M

= 1.202 x10^-3 moles

(2) 1 mole of Na2S2O3 reacts with 2 mole of NaClO, so moles of ClO^- = 0.5 x 1.202 x10^-3 moles = 0.6x 10^-3 moles

(3) Mass of NaClO = moles x Molar mass

= 1.202 x10^-3 moles x 74.442 g/mol

= 0.09 g

(4) You didnt give initial volume of bleach solution taken.

So assume that initialy you took 1 mL of solution.

Then initial mass of bleach = 1 mL x 1.040 g/mL

= 1.040 g

weight percent of NaClO == (0.09 /1.040 ) x 100

= 8.7%