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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