Chapter 10, Problem 28PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# A 0.0130-g sample of a gas with an empirical formula of C4H5 is placed in a 165-mL flask. It has a pressure of 13.7 mm Hg at 22.5 °C. What is the molecular formula of the compound?

Interpretation Introduction

Interpretation:

The molecular formula of the compound has to be determined.

Concept Introduction:

density=PMRT

P-PressureM-MolarmassR-UniversalgasconstantT-Temperature

Explanation

Given that:

Â Â Â Â Â massâ€‰ofâ€‰theâ€‰compoundâ€‰=â€‰0.0130â€‰gvolumeâ€‰â€‰â€‰â€‰â€‰=â€‰165â€‰mlâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰0.165â€‰LPressureâ€‰=â€‰13.7â€‰mmâ€‰Hgâ€‰â€‰=â€‰0.018â€‰atmTemperatureâ€‰=â€‰22.5Â°Câ€‰â€‰â€‰=â€‰295.5â€‰K

The molecular formula of the given gas can be calculated as

â€‚Â densityâ€‰=â€‰massvolumeâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰0.0130â€‰g0.165â€‰Lâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰0.07878â€‰g/L

Using this density we can calculate the molar mass of the compound.

â€‚Â densityâ€‰=â€‰PMRT

â€‚Â Mâ€‰â€‰â€‰=â€‰â€‰dRTPâ€‰=â€‰0

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