What is the molar mass of the unknown liquid? (Step 5) Use the table in the expe
ID: 501956 • Letter: W
Question
What is the molar mass of the unknown liquid? (Step 5) Use the table in the experiment print out to identify the liquid.
Atmospheric pressure = 765 mmHg
Mass of empty flask = 120.30g
Mass of flask with liquid at the end = 121.00g
Temperature = 100oC
Volume of flask = 285mL
Volatile Liquid
Molecular Weight (g/mol)
Boiling Point (°C)
Acetone
58.1
56.5
2-Butanone
72.1
79.6
Cyclohexane
84.2
80.7
Ethanol
46.1
78.5
Ethyl Acetate
88.1
77.1
1-Heptene
98.2
93.6
Hexane
86.2
69.0
Methyl Acetate
74.1
57.0
2-Propanol
60.1
82.3
Volatile Liquid
Molecular Weight (g/mol)
Boiling Point (°C)
Acetone
58.1
56.5
2-Butanone
72.1
79.6
Cyclohexane
84.2
80.7
Ethanol
46.1
78.5
Ethyl Acetate
88.1
77.1
1-Heptene
98.2
93.6
Hexane
86.2
69.0
Methyl Acetate
74.1
57.0
2-Propanol
60.1
82.3
Explanation / Answer
First, note that
Molar Mass = mass of sample / mol of sample
so
mass of liquid = mass of liquid + flask - mass of flask = (121.000 - 120.30)
mass of liquid/sample = 0.30 g
now, find / calculate moles
PV = nRT
n = PV(RT)
n = (765)(0.285)/(62.4*373)
n = 0.009367 moles
then
MM = 0.30/0.009367 = 32.07 g/mol
Nearest answer is either:
O2(g) with MW = 32 g/mol
or
Methanol = 32 g/mol
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