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P-7
i)
the black wire to the common outlet,
ii)
the red wire to the 200 mA outlet,
iii)
the dial to the 200 mA position on the AMP scale (bottom scale),
NOTE:
This 200 mA setting MUST be made BEFORE any current passes through the
system; therefore, turn to this setting NOW and leave the multimeter “ON” until the
end of the lab session and then turn it off.
iv)
the dial of the resistance board set to the “I” (inital start) position. This should give an
initial current of ~80 - 100 mA.
At this point, have your instructor check that the apparatus is properly assembled.
Once you have received your instructor’s approval, connect the leads to the power supply, very briefly, to
check the current. You should have a current of about 100 mA. Immediately, unplug one of the leads
from the power source. Record the temperature, the barometric pressure, and the initial buret volume.
Note the time to the nearest second when you plug in the DC power source to start the electrolysis; record
this time on your Observations Sheet. If you are using a stopwatch, this will be t = 0.00 minutes. If not,
record the time in minutes and seconds.
As quickly as possible, use the knob on the resistance board to adjust the current to approximately
135 mA. Try to maintain a relatively constant current of about 130 mA to 140 mA through the duration of
each run. This will minimized errors in your calculations. The electrolysis should continue until the water
column is less than 5 cm. This should take about 20-25 minutes.
When you have collected enough hydrogen gas, note the time when you disconnect the power lead.
Immediately record the time, buret reading and the height of the water column remaining in the buret
on your Observations Sheet. Rinse, air-dry and re-weigh the copper electrode. Be sure that the copper
wire is dry before recording the mass.
Do at least one more run, making sure that the copper electrode surface is clean and that all of your electrical
connections are tight.
