Scenario:A student diluted 50.00 mL of a commercial bleach to 250.00 mL in a volumetric
flask and then titrated a 20. mL aliquot. The titration required 35.50 mL of 0.10000 M Na 2 S 2 O 3
solution. The price of the gallon jug of bleach was $1.00. The density of the bleach was
1.15 g ⋅mL–1.
Analysis:
- Calculate the number of moles of S 2 O 3 2–ion required for titration.
.'
'
''.
.mL Na S O sol n
mL Na S O sol nL sol nL sol nmol Na S O
mol Na S Omol S O
mol S O135 50
1000110 10000
11
3 550 1022 3
22 3
22 3
22 32 3 3(^23)
=
- -- 2
2
- Calculate the number of moles of I 2 produced in the titration mixture.
.. mol S O
mol S O
mol I 1 775 10 mol I
13 550 10
21 3
2(^32)
3
(^23)
## (^2) = -
--
2
2- Calculate the number of moles of OCl–ion present in the diluted bleaching solution that
was titrated.
.. mol I
mol I
mol OCl 1 775 10 mol OCl
11 775 10
1(^21)
2
3
#^3
##=
- Calculate the mass of NaOCl present in the diluted bleaching solution titrated.
. mol OCl.
mol OCl
mol NaOCl
mol NaOClg NaOCl
11 775 10
11
174 44
#^3
##
= 0.1321 g NaOCl
- Determine the volume of commercial bleach present in the diluted bleaching solution
titrated (aliquot).
.
.
mL.
mLmL commercial bleach
120 00
250 00diluted bleach sol’n 50 00
# diluted bleach sol’n= 4.00 mL commercial bleach- Calculate the mass of commercial bleach titrated.
.
.
mL commercial bleach.
mL commercial bleachg commerical bleach
1400
100115
# = 4.60 g commercial bleach- Determine the percent NaOCl in the commercial bleach.
%.
.
whole %.%part
g commercial bleachg NaOCl(^100460)
0 1321
##== 100 2 87
- Calculate the mass of 1.00 gallon of the commercial bleach. 1 U.S. gallon = 3785 mL.
..
..
gal comm bleach ..
galmL
mL comm bleachg comm bleach
1100
13785
100115
= ## = 4.35 × 103 gPart III: AP Chemistry Laboratory Experiments