Question

How many lanthanum atoms are in 69.5g lanthanum?

Answer 1

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"`