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T-7
Similarly, measure into each 100 mL beaker:
10.00 mL (NH
4
)2S2O
8
from the buret and 2 drops of EDTA
NOTE:
The volumes used do not need to be a specific preset amount. They need only to be
close, but they must be accurately measured (i.e. to 0.02 mL). Record all buret
measurements on your Observations Sheet.
NOTE:
Remember to add 2 drops of EDTA
*
to each container.
Place one set of solutions into a cold water bath to equilibrate and one set into a warm water bath to
equilibrate while you perform the room temperature runs.
NOTE:
The temperature of the reaction solution in the flask is the temperature for the
reaction run that is to be recorded on your Observations Sheet.
Run 1 -
Room Temperature Run
Record the temperature of solution in the flask. Leave the thermometer in the flask, have
your timer ready and quickly pour the solution from the beaker into the flask. Start the
timer as soon as the two solutions make contact. Swirl the solution gently to promote
mixing. Continue to swirl the solution in the flask until the first trace of blue appears. The time
for the reaction should be taken from the point of mixing (i.e. t = 0) to the first appearance
of the blue color. Immediately record the reaction time and the temperature of the
reaction solution to ±0.1°C on your Observations Sheet.
Run 2 -
Prepare the two solutions in the beaker and flask respectively then warm the solutions by
immersing the containers in warm water in the water bath set at
32
C, so that the final
temperature will be about 10°C above room temperature. Once the solutions are at
approximately this temperature and are within 2
C of each other, mix the solutions.
Record the reaction time and the temperature of the reaction solution to ±0.1°C
on your
Observations Sheet.
*
Traces of copper from previous experiments may catalyze this reaction. EDTA is added to the solutions to complex
with any stray metal ions that might be present.
