How do you calculate molecular weight?

1 Answer
anor277
Jul 3, 2016

Typically we calculate a molar mass, i.e. a mass of a given quantity of molecules. The given quantity is #N_A#, #"Avogadro's number"# #=# #6.022xx10^23*mol^-1#.

Explanation:

#"Avogadro's number"# of #""^1H# has a mass of #1.00*g# precisely; #"Avogadro's number"# of #""^12C# has a mass of #12.00*g# precisely. If I have #"Avogadro's number"#, #6.022xx10^23#, individual #""^12C^1H_4# molecules, it follows that I have #(4xx1.00+12.00)*g#. Typically we would say methane has a molar mass of #16.00*g*mol^-1#

You will never be asked to remember these atomic masses, mind you will certainly pick up and learn some of them by memory, because they will be available on a Periodic Table of Elements, that will be issued in every chemistry and physics exam.

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