How many lanthanum atoms are in 69.5g lanthanum?

1 Answer
Aug 20, 2017

Answer:

There are #3.01xx10^23# atoms of La in #"69.5 g La"#.

Explanation:

The given mass of lanthanum (La) must be converted into moles. One mole of atoms is #6.022xx10^23# atoms. The molar mass of La is #"138.90547 g/mol"# (from periodic table).

To determine mol La, divide the given mass by its molar mass. Since molar mass is a fraction, #"g"/"mol"#, multiply the given mass by the inverse of the molar mass. Then multiply by #6.022xx10^23# atoms/mol.

#69.5color(red)cancel(color(black)("g La"))xx(1color(red)cancel(color(black)("mol La")))/(138.90547color(red)cancel(color(black)("g La")))xx(6.022xx10^23"atoms La")/(1color(red)cancel(color(black)("mol La")))=3.01xx10^23" atoms La"#