Exp. 8:
Molar Volume of Nitrogen
Required Locker Materials:
- Gas apparatus (see figure)
- Small vial
- Standard test tube
Safety:
- Eyewear MUST be worn at all times
Waste:
- All liquid waste must be disposed in the
waste containers.
Experimental Objective:
The object of the lab is to determine the molar volume of nitrogen N2 at the temperature
and pressure prevailing in the laboratory. In a second step the molar volume at STP will be
calculated.
Students will learn to combine a stoichiometry problem with a gas law problem. At the
same time this will be the first lab students will experiment with gases and learn how to
measure gas volumes.
Introduction:
When sulfamic acid (HSO3NH2) is mixed with sodium nitrite (NaNO2) nitrogen gas is
produced according to the equation:
NaNO2 + HSO3NH2 → NaHSO4 + H2O +N2 ↑
If an excess of sodium nitrite is used, all of the sulfamic acid can be decomposed.
According to the reaction above nitrogen gas is produces which can be collected over water.
Procedure
For this experiment record all observations and
measurements in your notebook:
1. Set up the apparatus as shown, except
move the leveling bulb higher and closer to
the test tube. Fill the leveling bulb about
half full of water. Check for leaks.
2. Weigh out about 0.15 grams of sulfamic acid
(write down your measured amount) and
place it in a small vial.
3. Weigh out about 0.14 grams of sodium
nitrate and dissolve it in about 5 mL of
distilled water in a 15 cm test tube. Be sure
the water won’t run into the vial when it is
dropped inside the test tube.
4. Stopper the test tube, connecting it to the
rubber tubing attached to the gas buret.
Align the water levels and record the initial
volume.
5. Tilt the test tube sideways so that the
sodium nitrite and sulfamic acid mix. The
nitrogen evolved will force water into the
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Leo Truttmann – Fall 13
leveling bulb. Keep mixing until no more bubbles appear to be in generated. Wait an
additional 5 to 10 minutes to make certain temperature of the system has returned to
room temperature.
6. Realign the water levels. (This insures that the pressure in the system is the same as
barometric pressure.)
7. Record the final volume. Also record the barometric pressure and the temperature of
the room
8. Repeat the experiment a second time with a fresh batch of reactants. Record the
pertinent information on the data sheet.
Calculations
For the calculation start a new section in your notebook. Remember you need to show
every calculation you do by writing down the equation and an example calculation. The
example calculation only needs to be done for one trial. The results of the remaining trials
can be written down in a table in your notebook.
Volume of evolved nitrogen gas
The volume of nitrogen is the difference between your initial and final volume reading with
your gas buret.
Vapor pressure of water
The vapor pressure of water only depends on the temperature. Read the vapor pressure
from a table based on the measured room temperature. Make sure you write down the
correct unit.
Moles of nitrogen
The sulfamic acid used in the reaction should be limiting (check!). Therefore the moles of
nitrogen produces can be calculated using stoichiometry.
Molar Volume of nitrogen under Lab conditions
You measure a volume of nitrogen evolved based on a small amount of nitrogen produced.
Scale this up and calculate how large of a volume would be produced if you reacted one
mole of nitrogen under Lab conditions.
Partial pressure of nitrogen
The pressure of nitrogen in your apparatus is less than the atmospheric pressure in the lab.
The difference is that nitrogen was collected over water which exerts a small pressure called
vapor pressure.
Molar Volume of nitrogen under STP
Using the combined gas law calculate the molar volume of nitrogen under STP conditions,
which are different from the Lab conditions.
Average Molar Volume of nitrogen under STP and %error
Calculate the average Molar Volume under STP conditions and calculate the % error from
the accepted true value of 22.4 L/mole.
Exp. 8:
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Leo Truttmann – Fall 13
Experiment 8: Molar Volume of Nitrogen
Name:_______________
Date:
Trial 1
Trial 2
Measurements
Mass sulfamic acid
[g]
Mass sodium nitrite
[ml]
Volume initial
[ml]
Volume final
[ml]
Room temperature
[C]
Barometric pressure
[mmHg]
Calculations
V(nitrogen gas)
[ml]
Vapor pressure of water
moles of nitrogen = moles of sulfamic acid
[mol]
Molar Volume of nitrogen (Lab conditions) = (V/n)
[L]
Partial Pressure of N2 = Barometric pressure - vap. Pressure
[atm]
Molar Volume of nitrogen at STP
[L]
Average Molar Volume at STP
% error (True value = 22.4 L/mole)
Exp. 8:
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Leo Truttmann – Fall 13