Question

Question #24a9d

Answer 1

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`.
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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`.