This preview shows pages 1–2. Sign up to view the full content.
Christina Wong
AP Chemistry 4
th
hour
3/31/2010
Determining the Molecular Mass of a Gas
I.
Purpose
The purpose of this lab was to determine the molecular mass
of a substance from measurements of the density of its
vapor.
II.
Observations and Data
Mass of flask + cap
83.96 g
Mass of flask + cap + condensate
84.34 g
Volume of flask (V
1
)
125 mL
Temperature of water, (T
1
)
98 C = 371 K
Barometric pressure
29.98 inHg = 761.5 mmHg
III.
Calculations
1.
Find the mass of the condensed vapor:
Mass = part b – part a
Mass = 84.34 – 83.96 =
0.38 g
2.
Find the volume of the vapor at STP:
V
2
=V
1
x P
1
x T
2
/P
2
x T
1
V
2
=125mL x 761.5 mmHg x 273 K / 760 mmHg x 371 K
V
2
=
92.16 mL
3.
Find the molecular mass of the gas sample
Molecular mass = m (g) x 22.4 (L/mole) / V
2
(L)
Molecular mass = 0.38 g x 22.4 L/mole / 0.09216 L
Molecular mass =
92.36 g
IV.
Conclusions and Questions
1.
Using the molecular formula supplied by the teacher, calculate the actual
molecular mass of the unidentified substance.
The actual molecular mass of ethanol (C
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 Spring '11
 kk

Click to edit the document details