Academic Chemistry Lab: Utilizing Dalton’s Study (18 points)
(page 1 of 2)
OBJECTIVE: After completing this lab, students should be able to determine the mass of
magnesium needed to produce a given mass of hydrogen from a reaction after
correcting for water vapor pressure.
APPARATUS: 2L pop bottle w/ open top, 50mL graduated eudiometer tube, thermometer
MATERIALS: magnesium ribbon (do not heat)
12M HCl (hydrochloric acid) - very strong irritant
aluminum wire, copper wire, or thread
INTRODUCTION: The law of definite composition should hold true for all compounds.
Therefore it is possible to find out how many grams of one element are needed to combine with
one gram of another element. As a rule metals do not readily combine with hydrogen; however,
metals will displace hydrogen from solutions. Magnesium will react with HCl and liberate H2
gas. In this lab you will determine how many grams of magnesium are required to replace some
H2 from HCl. In this lab you will also determine the mass of an unknown mass of Mg ribbon by
measuring the volume of hydrogen liberated and correct for water vapor pressure.
PROCEDURE:
1. Fill an open 2L pop bottle with tap water that is near room temperature. Roll a length of Mg
ribbon of known mass into a loose coil. Tie this coil with one end of wire that is
approximately 25 cm long. Pour 5mL 12MHCl into the eudiometer. Add enough tap water
to fill it completely, being careful not to mix the water and the acid. Lower the Mg coil into
the water of the eudiometer to a depth of about 5 cm. Close the tube with your thumb so that
no water escapes and the Mg coil is locked in place. Taking care that no air enters, invert the
eudiometer into the open pop bottle and allow it rest against the bottom. You might want to
clamp the eudiometer in place on a ring stand. Why does the acid flow down the tube? Is
this acid now concentrated or dilute?
2. When the Mg is completely consumed and the reaction has stopped; adjust the tube so that the
liquid levels are inside and outside the eudiometer are the same. Add tap water that is near
room temperature if necessary. Why is it important that the liquid levels be the same? If the
temperature of the water and the room temperature are not exactly equal, what would be a
reasonable temperature to use in your calculation?
3. Record the volume of the gas collected, the pressure of the atmosphere when the data was
collected, the mass of Mg ribbon reacted, and a reasonable temperature of the gas collected.
4. Repeat procedure one; however, this time use an unknown mass of Mg ribbon. Record all
pertinent information in the proper data table.
Lab Team Names ________________________________________________ period _______
Academic Chemistry Lab: Utilizing Dalton’s Study (18 points)
(page 2 of 2)
(all data should have at least 2 significant figures)
DATA TABLE ONE: known mass Mg (2pts)
mass Mg reacted
volume gases collected
temp gases collected
atmospheric pressure
torr
Pwater at gas temperature
torr
pressure dry H2 collected
torr
moles dry H2 collected
mass Mg (calculated)
percent error mass Mg
DATA TABLE 2: unknown mass Mg (2pts)
volume gases collected
temp gases collected
atmospheric pressure
torr
Pwater at gas temperature
torr
pressure dry H2 collected
torr
moles dry H2 liberated
calculated mass Mg reacted
CALCULATIONS: (2 points each)
1. Starting with the volume of gases collected in data table one, show a smooth calculation that
determines the moles dry H2 collected.
2. Starting w/ moles dry H2 collected show a smooth calculation that determines the mass Mg
that should have reacted.
3. Show a smooth calculation that determines the % error between the calculated and measures
mass Mg. % error = +/- (measures mass – calculated mass)/measured mass x 100
4. Starting with volume of gases collected in data table two, show a smooth calculation that
determines the unknown mass of Mg.
QUESTION: (2 point)
List four possible sources of error in collecting your data that could affect your calculated values.
Don't list anything that can be attributed to human error.
water vapor pressure
temp pressure
‘C
mm Hg
0.0
4.6
5.0
6.5
10.0
9.2
12.5
10.9
15.0
12.8
15.5
13.2
16.0
13.6
16.5
14.1
17.0
14.5
17.5
15.0
temp
‘C
18.0
18.5
19.0
19.5
20.0
20.5
21.0
21.5
22.0
22.5
pressure
mm Hg
15.5
16.0
16.5
17.0
17.5
18.1
18.6
19.2
19.8
20.4
temp
‘C
23.0
23.5
24.0
24.5
25.0
26.0
27.0
28.0
29.0
30.0
pressure
mm Hg
21.1
21.7
22.4
23.1
23.8
25.2
26.7
28.3
30.0
31.8
temp
‘C
35.5
40.0
50.0
60.0
70.0
80.0
90.0
95.0
100.0
pressure
mm Hg
42.2
55.3
92.5
149.4
233.7
355.1
525.8
633.9
760.0