Suppose a student diluted and titrated a bleach unknown exactly as described in

Question

Suppose a student diluted and titrated a bleach unknown exactly as described in the experimental procedure, except only a single titration was performed which required 12.63 mL of 0.100 M Na2S2O3.

The density of the original, undiluted bleach unknown was 1.05 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 of the hypochlorite ion comes from sodium hypochlorite.

4-Calculate the grams of NaClO in the titrated bleach sample, assuming all of the hypochlorite ion comes from sodium hypochlorite.

5-Calculate the mass in grams of UNDILUTED bleach that was in the sample of bleach titrated.

6-Using the answers to questions 3 and 4, calculate the weight percent of NaClO in the undiluted bleach sample.

Explanation / Answer

(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 10-3moles

(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%

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