Question

The molar mass of `NO_2` is 46.01 g/mol. How many moles of `NO_2` are present in 114.95 g?

Answer 1

`"2.498"`

Explanation:

A substance's molar mass tells you the mass of one mole of that substance.

In your case, nitrogen dioxide, `"NO"_2`, is said to have a molar mass of `"46.01 g/mol"`. That means that every mole of nitrogen dioxide will have a mass of `"46.01 g"`.

So, in essence, molar mass is simply a conversion factor between number of molecules and mass.

Since you need `"46.01 g"` of nitrogen dioxide in order to have one mole of the compound, it follows that `"114.95 g"` will contain

`114.95 color(red)(cancel(color(black)("g"))) * "1 mole NO"_2/(46.01color(red)(cancel(color(black)("g")))) = "2.49837 moles NO"_2`

Rounded to four sig figs, the number of sig figs you have for the molar mass of the compound, the answer will be

`n_(NO_2) = color(green)("2.498 moles")`