Determination of the Molar Mass of Carbon Dioxide

1
Determination of the Molar Mass of Carbon Dioxide

• Experiment 4

2
Experiment 4

• Goal
• To determine molar mass of CO2 gas
• Method
• Collect CO2 gas generated by a reaction
• Use the ideal gas law and the equation for molar
  mass

3
Ideal Gases

• Pressure, P
• Temperature, T
• Volume, V
• Amount, n
• Proportionality constant
• Universal Gas Constant, R
• 0.08206 L.atm 62.4 L.atm
• K.mol K.mol

4
Universal Gas Constant, R
n,T const.
n, V const.
n, P const.
5
Molar Mass of a Gas
Ideal Gas Law
Molar mass
So
and
6
CO2

• Reaction
• Requires
• T in Kelvin C 273 (0.5)
• P in atm barometer in hall
• V in L volume of water in flask
• graduated cylinder (1mL)
• Mass in g analytical balances. (0.0001g)

7
Procedure

• Assemble Dumas Bulb (collection flask)

Mass
mDumas air mDumas mair
Volume
How could you find this?
8
Procedure

• Assemble Generation Flask

9
Procedure

• Generate CO2(g)

HCl
NaHCO3
Closed valve
10
Procedure

• Generate CO2(g) and collect 1 minute

Open valve slowly
Collect gas
Note if reaction is exothermic or endothermic
11
Procedure

• Record massDumasgas massDumas massgas

Keep top open
Also record barometric pressure and temperature
12
Procedure/Calculations

• What is the mass of the Dumas bulb?

Hint p 197
Find MMair before lab
13
Procedure/Calculations

• What is the mass of CO2?

Find mCO2 and sm,CO2 using best trials
right!
14
Procedure

• Calculations and error propagation
• mCO2 from multiple measurements
• Find error in MMCO2 (sum of relative errors)
• Use one equation (round once)

Compare MMCO2 to actual MM Include error and
discuss
15
Humidity/Sources of error

• If Patm 760 torr and T 20oC
• H2O at 100 humidity 17.5 torr
• 78 N2 PN2 593 Torr
• 21 O2 PO2 160 Torr
• 1 Ar PAr 7.6 Torr

How would extra water vapor affect results?
16
Report

• Abstract
• Data/Results
• Sample calculations including
• Molar mass of air and mass of air in bulb
• Individual and average mass of gas in bulb
• Average molar mass of gas in bulb
• Error analysis
• Discussion/review questions