Question #24a9d

1 Answer
Dec 21, 2017

Answer:

Needless to say, they are different. The molecular weight is the sum of the atomic weight.

Explanation:

[What is the atomic mass?]
The atomic mass is the average mass of an element. It is the relative mass compared to #""^12C#.
https://www.pinterest.jp/pin/264023596881882763/

Example:
#""^12C=12# amu (by definition)
#""^13C=13.003355# amu
(http://www.sisweb.com/referenc/source/exactmas.htm)

The abundance(%) for #""^12C# and #""^13C# are #98.90# and #1.10#, respectively.
Therefore, the atomic mass of carbon is
#12*0.9890+13.00*0.0110=12.011#.

[What is the molecular mass?]
The molecular mass is the average relative mass of an molecule, compared to #""^12C# atom. It is the sum of the atomic mass in the molecule.

For example, the atomic mass of hydrogen is #1.008#, and the molecular mass of hydrogen(#H_2#) is #2*1.008=2.016#.
The molecular mass of methane(#CH_4#) will be #12.011+4*1.008=16.043#.