 |
 |
5 of 11 |  |
 |
 |
D-5
EXPERIMENTAL PROCEDURE
Safety glasses must be worn at all time in the laboratory.
Record all of your results on the Observations Sheet in ink.
Before assembling the apparatus, both the 250 mL Erlenmeyer flask and vial must be thoroughly cleaned.
Clean the flask and vial, however, do not use soap!. Rinse both the vial and flask four times with tap
water and then rinse twice with deionized water.
Set up the apparatus as shown in Figure 1. Add approximately 350 mL of tap water at room temperature
(provided in a specially marked carboy) to the 400 mL beaker. Set up the buret so that the stopcock is at the
top and the open end of the buret is below the surface of the water in the beaker (See Figure 1).
A U-tube connected with clear tubing to a glass tube in a rubber stopper is provided for you to use. Insert
the U-tube into the mouth of the buret as shown in Figure 1, then lower the buret and U-tube to the bottom
of the beaker. Insert a rubber stopper into the mouth of the Erlenmeyer flask.
With the stopcock open, place a squeeze bulb (with the air expelled) over the tip of the buret and draw
water into the buret by slowly releasing the pressure on the bulb. Close the stopcock if you need to remove
the bulb to squeeze it again in order to draw more water into the buret.
Run 1:
The sulfamic acid solution that you are to use has been prepared and is to be accurately dispensed from
burets that at set up in the laboratory for common use. For Run 1, accurately measure approximately 8.xx
mL of the sulfamic acid solution into the clean 250 mL Erlenmeyer flask. Record the initial and final buret
readings on your Observations Sheet.
Note:
All buret readings must be recorded to 0.01 mL accuracy. A buret reading card must be used to
read burets accurately. For example, the initial reading might be 21.74
mL. (If most of your
readings end in 0 or 5, you probably are not making the readings correctly, and you will have
mark(s) taken off.) Ask your laboratory instructor for help if you are having problems
reading your buret.
Using the automatic dispenser, add 10.00 mL of the NaNO2 solution into the clean glass vial. Using long
tweezers, carefully lower the vial into the Erlenmeyer flask, so that the vial stands upright on the bottom of
the flask. Be careful not to splash out any NaNO2 from the vial into the sulfamic acid, or the reaction will
start prematurely. Carefully stopper the Erlenmeyer flask with a rubber stopper so that the system is
airtight.
For Run 1, set the level of water in the buret to ~ 26 mL. Accurately read the water level in the buret and
record this level on your Observations Sheet where it asks for the initial buret reading for Run 1. To start
the reaction, tilt the flask so that the vial tips over and the sulfamic acid solution enters the vial. Initially,
