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O-6
The KMnO
4
solution is available in squeeze bottles on the front bench. Use these bottles to dispense
the KMnO
4
solution into your buret. Rinse a clean buret twice with
5 mL of the KMnO
4
solution that
is to be standardized. Discard this rinse solution in your toxic waste beaker. Fill this buret with the
KMnO
4
solution.
Pour about 15 mL of the oxalic acid solution into a clean, dry 50 mL beaker and use this solution to
rinse a 10 mL volumetric pipet. Do not place the pipet in the volumetric flask. Always pipet from the
50 mL beaker. The solution in the volumetric flask should never be contaminated by the pipet. After
thoroughly rinsing the pipet, discard the remaining oxalic acid from the beaker and refill the beaker with
40 mL of oxalic acid from the volumetric flask. Pipet 10.00 mL of oxalic acid (from the beaker) into a
clean Erlenmeyer flask (minimum 200 mL). Add about 30 mL of distilled water and 1 mL of 6 M
H2SO
4
solution to the sample and heat it to near boiling and then quickly titrate this sample with the
KMnO
4
solution until the first permanent appearance of a pale pink color appears. While this
solution is heating, repeat the above procedure to obtain 2 more samples of oxalic acid (10.00 mL in
200 mL Erlenmeyer flasks). Heat these samples as well so that they are ready to use immediately.
NOTE:
i)
The meniscus of the KMnO
4
solution is difficult to read because of the dark purple
color of the solution. To make the buret readings, pick a point on the meniscus that is
the best for you to read and consistently make all your readings using this point as the
level to read.
ii)
The color of the end point should be the palest pink possible, therefore place the
Erlenmeyer flask on a piece of white paper so that the end point can be easily
seen.
iii)
The reaction titration solutions may need to be reheated for a few minutes
during the titration if the transient pink color lingers too long.
Remember to record the initial and final buret readings on your Observations Sheet in order to calculate
the volume of the KMnO
4
used in the titration. Repeat the titration of 10.00 mL samples of the
standard oxalic acid solution until three consistent volumes (+ 0.1 mL) of the KMnO
4
titrant required
are obtained.
