Graduated cylinders are not as precisely calibrated as burets or volumetric pipets. Briefly
explain why it is acceptable to measure the Kl and HCl solutions used in the titration with
graduated cylinders rather than with pipets or burets.
It is acceptable to measure the Kl and HCl solutions used in the titration with graduated
cylinders rather than with pipets or burets because we are not after a specific amount, we
are after excess.
Would the following procedural errors result in an incorrectly high or low calculated per-
cent NaOCl in commercial bleaching solution? Briefly explain.
(1) A student failed to allow the volumetric pipet to drain completely when transferring
the diluted bleaching solution to the Erlenmeyer flask.
If a student failed to drain completely the volumetric pipet when transferring the di-
luted bleach, this error would result in an incorrectly low percent of NaOCl. NaOCl
is the active ingredient in bleach. If incorrect low amounts are transferred to the
Erlenmeyer flask, then the NaOCl concentration is also incorrect.
(2) A student blew the last drops of solution from the pipet into the volumetric flask
when transferring commercial bleaching solution to the flask.
If a student blew drops of commercial bleaching solution into the volumetric flask,
then that student has introduced another set of chemicals from the moisture of their
mouth into the solution, altering the experiment and altering the results.
(3) A student began a titration with an air bubble in the buret tip. The bubble came out of
the tip after 5 mL of Na 2 S 2 O 3 solution had been released.
Having a bubble in the buret tip containing 5 mL of Na 2 S 2 O 3 results in an incorrectly
high calculated percent NaOCl in the commercial bleaching solution. Na 2 S 2 O 3 is used
to determine the amount of I 2 formed by titration. It reconverts I 2 made from the reac-
tion of OCl–ion and I–ion into I–ions again. So, transferring less Na 2 S 2 O 3 to the
pipet, affects the concentration of OCl–ion in the bleaching solution.
An overly efficient student simultaneously prepared two titration mixtures, consisting of
diluted bleaching solution, KI solution, and HCl solution. The student found that data
from the two titrations yielded significantly different percents NaOCl in the commercial
bleaching solution. Which determination would give the higher % NaOCl? Briefly
explain.
Based on my results, I believe the first determination would yield higher NaOCl simply
because more care is put into one determination than the other, because as you titrate, the
diluted bleach solution must be agitated constantly throughout the Na 2 S 2 O 3 titration to no-
tice color change. So, since the student is working simultaneously, he cannot be precise
with the Na 2 S 2 O 3 concentration he titrates into the flask.
