What mass of gold, Au, contains the same number of atoms 9.0 g of aluminum, Al?

1 Answer
Meave60
Nov 26, 2015

#"9.0 g Al"# contains #2.0xx10^23"atoms Al"#.
#2.0xx10^23"atoms Au"# has a mass of #"65 g"#.

Explanation:

First determine the number of atoms in #"9.0 g Al"#.

Divide the given mass of #"Al"# by its molar mass (atomic weight on the periodic table in g/mol), then multiply times #6.022xx10^23"atoms/mol"#, which is the same for all elements.

#9.0cancel"g Al"xx(1cancel"mol Al")/(26.982cancel"g Al")xx(6.022xx10^23"atoms Al")/(1cancel"mol Al")=2.0xx10^23 "atoms Al"#

Now reverse the process to determine the mass of gold that contains #2.0xx10^23"atoms Au"#.

Divide the calculated atoms by the number of atoms in one mole, then multiply times the molar mass of #"Au"#.

#2.0xx10^23cancel"atoms Au"xx(1cancel"mol Au")/(6.022xx10^23cancel"atoms Au")xx(196.967"g Au")/(1cancel"mol Au")="65 g Au"#

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