Ideal Gas Law
CHEM 251
Week of October 25th, 2010
Alexis Patanarut
For the week of November 1st , 2010
• Experiment: Absorption Spectroscopy, pp.
37-48
• Quiz: material in lab manual
• Due next week: Ideal Gas Law lab report
Overview
• A sample of an unknown metal will be reacted
with HCl, producing hydrogen gas and a watersoluble metal chloride salt.
Unknown Metal #1 and #2:
M(s) + 2HCl(aq)  MCl2(aq) + H2(g)
Unknown Metal #3:
2M(s) + 6HCl(aq)  2MCl3(aq) + 3H2(g)
• This gas will be collected and its volume will be
measured. Using the Ideal Gas Law, n (number
of moles of gas produced) will be determined.
Procedure part I: Constructing the Apparatus
1.
2.
3.
4.
Fill a 1L beaker with tap water up to the 900mL mark.
Fill a 50mL graduated cylinder with water and place a piece of
weighing paper over the mouth of the cylinder. Holding the
weighing paper in place, quickly invert the cylinder and place it
into the 1L beaker. Temporarily clamp the cylinder in place.
Thread the rubber tubing of a pre-assembled stopper/gas
delivery system under the water line and into the mouth of the
inverted cylinder. Make sure this tube is in far enough so that it
will not come out during gas collection.
Place 10mL of 6M HCl solution into a medium test tube. Place
this test tube into a 250mL beaker. Place the stopper on the
test tube, taking care not to let the tube slip out of the cylinder.
The fit should be snug and prevent any gas leakage.
Procedure part II: Some Preliminary Measures
1. Obtain your unknown metal and measure the mass of the
sample to 3 decimal places. Prepare your sample for reaction
by either folding or rolling it carefully so that it will drop into the
test tube without become caught on the side of the tube.
2. Obtain readings for the temperature of the room and
atmospheric pressure. Convert these values into the same units
to use with the R constant 0.08206L*atm/mol*K.
3. Before you being the lab, make sure that you subtract any
trapped air that could have gotten into the cylinder during the
process of inverting it into the beaker.
•
Remember that you are reading the cylinder upside-down as you are
doing this. Initial start volume should be subtracted out after gas
collection is complete by Vf - Vi.
Procedure part III: The Experiment Itself
1.
2.
3.
4.
5.
Begin gas collection by carefully adding the metal sample into the acid
solution. Place the stopper IMMEDIATELY afterwards and make sure the fit
is snug. Wait until the metal completely dissolves before continuing.
Once the metal sample has dissolved, carefully remove the tube from the
mouth of the graduated cylinder.
The level of the water inside the cylinder will be either somewhat above or
below the level of water in the large beaker, so you will have to loosen the
clamp holding the cylinder and raise/lower the cylinder BY HAND until the
water level inside and outside the cylinder is the same. Record the volume.
Do at least two more trials using the same unknown metal. Your sample of
6M HCl should be enough to dissolve several more metal samples, so you
will only need to refill the water in the beaker as needed, re-invert the
cylinder, and replace the gas delivery tube into the mouth of the cylinder.
Use the data collected to determine n and use the value to identify the
unknown metal.
Your lab report should include the following:
• Raw data table (as downloaded)
• Class results data table
• Sample calculations
– n for your unknown metal sample
– determination of the molecular weight of your
unknown metal sample
– average of the three molecular weights
• For your Discussion/Conclusion section,
answer:
– Questions 1 and 3 in the experiment handout
(Further Questions for Thought and Review) and all
of the questions in the second handout (data
handout)