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 12.56 mL of 0.100 M Na2S2O3. The density of the original, undiluted bleach unknown was 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 mass in grams of UNDILUTED bleach that was in the sample of bleach titrated

5. Using the answers to questions 3 and 4, calculate the weight percent of NaClO in the undiluted bleach sample, in %w/w

Explanation / Answer

4NaOCl + Na2S2O3 + 2NaOH 4NaCl + 2Na2So4 + H2O

1. no of moles of Na2S2O3 = molarity * volume in L

                                            = 0.1*0.01256 = 0.001256moles

2. 1 mole of Na2S2O3 react with 4 moles of NaOCl

    0.001256 moles of Na2S2O3 react with = 4*0.001256/1 = 0.005024 moles of NaOCl

3. mass of NaOCl = no of moles* gram molar mass

                              = 0.005024*74.44 = 0.3739g

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