To calculate the mass of one individual molecule of #"CO"_2#, we need to
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Multiply the atomic mass of carbon by however many carbon atoms are in the compound (1)
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Multiply the atomic mass of oxygen by however many oxygen atoms are in the compound (2)
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Sum the total
1.
If we look at a periodic table, the mass number underneath the carbon symbol should read
#color(red)(12.011# #color(red)("amu"#
We multiply this value by the number of #"C"# atoms in the compound to find the total mass of carbon in one molecule:
#(1)(color(red)(12.011)color(white)(l)color(red)("amu")) = color(red)(12.011# #color(red)("amu"#
2.
We now do the same exact process for oxygen. Its atomic mass is
#color(green)(15.999# #color(green)("amu"#
There are #2# atoms of oxygen per molecule of carbon dioxide:
#(2)(color(green)(15.999)color(white)(l)color(green)("amu")) = color(green)(31.998# #color(green)("amu"#
3.
The mass of one molecule of #"CO"_2# is the sum of the masses of the constituent elements:
#"mass CO"_2 = color(red)(12.011# #color(red)("amu"# #+ color(green)(31.998# #color(green)("amu"# #= color(blue)(44.009# #color(blue)("amu"#
