Question

What is the total number of moles present in a 52.0 gram sample of `NaN_3`?

Gram-formula mass = 65.0 grams/mole

Answer 1

`"0.800 moles"`

Explanation:

The formula for calculating moles given the mass and a compound is:

`n = m/M`

`n` = moles
`m` = mass in grams `("g")`
`M` = molar mass `("g/mol")`

The molar mass is the sum of all the atomic masses in the compound.

`"Na" = "22.99 g/mol"`
`"N" = "14.01 g/mol" xx 3 ->` (there are `3` `"N"` atoms)

Add them up and you get `"65.02 g/mol"`

`n = m/M`

`= (52.0 cancel("g"))/(65.02 cancel("g")/"mol")`

`= "0.799753921 moles"`

`= "0.800 moles " ->` (rounded to three sig figs)

Therefore, there are `0.800` moles in 52.0g of `"NaN"_3`.

I hope this made sense :)