A chemist obtained two carbon dioxide cylinders from different suppliers
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A chemist obtained two carbon dioxide cylinders from different suppliers. The cylinders were labeled as containing CO₂ produced from either fossil fuel combustion (Cylinder E) or from plant biomass (Cylinder F). To verify the labels, the chemist ionized the CO₂ and recorded the mass spectra of the carbon atoms after fragmenting the molecules and isolating singly charged monatomic C⁺ ions.
The resulting data are summarized below.
m⁄z
Cylinder E intensity
Cylinder F intensity
12
9893
9590
13
107
410
(Natural carbon has isotopic abundances 98.93 % 12C and 1.07 % 13C.)
(a) Calculate the percent abundance of 13C in Cylinder F to two significant figures.
(b) Determine the average atomic mass of carbon in Cylinder F and compare it with the accepted atomic weight of 12.011 u. Express the difference as a percentage of the accepted value.
(c) Assuming the oxygen isotopic composition is natural, calculate the molar mass of CO₂ originating from Cylinder F to four significant figures.
(d) Explain why biogenic CO₂ (derived from recent plant biomass) often shows the kind of isotopic signature you calculated for Cylinder F.