Mole Concept: how it applies to alloys I was recently asked to find the total molar mass of a gold and palladium alloy, given the total number of atoms in the compound.
The method was to simply convert the total number of atoms to the total number of moles by using Avogadro's number as the conversion factor.

But as I understand it,  Avogadro's number and his concept only works if all the atoms are the same.  If multiple types of atoms are present in a group of $6.022\times10^{23}$ of them,  how could the different masses add up to a mole?
One mole is a number, not a mass.

See the following figurative example:

Let's say we are dealing with a sample of pure chemistry books.


A book's weight is 1 kg.
One mol of books would be 6,022 × 10²³ books.
The mass of one mol of books (the molar mass of books) would be as follows:


1 kg (mass of one book) × 6,022 × 10²³ (# of books)

Now let's say we're dealing with a mixture (alloy) of 60% chemistry and 40% history books. What is the mass of 1 mol of this mixture?


A history book's weight is 2 kg


So, our entire collection of books, sum up to Avogadro's number = 6,022 × 10²³ units. And we know that it is 60% Chem. and 40% Hist. So the mass of the entire collection would be:

m = N × 0,6(1kg) × 0,4(2kg)

where N is the Avogadro's number.



Enough of analogies. You have the mass of the gold and palladium atoms from the periodic table. I am assuming you also have the proportion Au/Pd.

You also know that there's 1 mol of atoms. The exact same equation would apply:

m = N × P.M(Au) × P.M(Pd)

where N is the Avogadro's number, P and M are the percentages and atomic mass, respectively, of gold and palladium.