Average molar mass

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Average molar mass

Postby AnvitaaAnandkumar_1B » Tue Oct 01, 2019 8:49 pm

In the text under section E, in order to find the average molar mass for elements that have isotopes, they have first found the average atomic mass and then multiplied by Avogadro's constant to get the average molar mass.
However, if in a question we are presented with the atomic mass, molar mass number of isotopes and percentage composition, can we simply disregard the atomic mass and multiply the molar mass of each isotope by it's percentage composition to obtain the average molar mass of the element?

Michael Du 1E
Posts: 117
Joined: Sun Sep 22, 2019 12:16 am

Re: Average molar mass

Postby Michael Du 1E » Tue Oct 01, 2019 10:15 pm

I believe so, but majority of the times, the problems will only present us with the atomic mass and the composition of each isotope. Therefore we would have to use the avogadro's number to multiply. But if the atomic mass and molar mass of the isotopes composition are given, there would be no need to multiply with avogadro's number as doing so would give an answer with the units of g/mol^2. This is rarely the case though, I assume.

Dakota Walker 1L
Posts: 58
Joined: Wed Sep 18, 2019 12:17 am

Re: Average molar mass

Postby Dakota Walker 1L » Tue Oct 01, 2019 10:16 pm

Yes, if you are trying to find the molar mass of an isotope you can ignore the average atomic mass and multiply the atomic mass of the isotope by avogadro's number.

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