Question

How many grams are there in 4.50 moles of `Ba(NO_2)_2`?

Answer 1

number of moles (n) = 4.50 moles
mass (m) = `n xx M` [This is what you are trying to find]
molar mass (M) = ?

Your first step is to find out what is the molar mass (M) of `Ba(NO_2)_2`.

To find a molar mass of a compound, break the compound up into component parts so you could see what elements are involved.

If you break `Ba(NO_2)_2` up, you can clearly see that it is composed of Ba, N and O.

You got to find the molar mass of each elements involved. You can identify the molar mass straight away if you look into the periodic table.

Ba = `137.3 g mol^-1`
N = `14.0 xx2` because there is a number 2 after the closing bracket so `28.0 g mol^-1`
O = There are 2 O atoms inside the bracket and doubled because of the 2 outside the closing bracket, so there are 4 O atoms altogether. `16.0 g mol^-1 xx 4 = 64.0 g mol^-1`

So to get the molar mass of `Ba(NO_2)_2`, add the molar mass of the elements up. `137.3 + 28.0 + 64.0` and that will give you `229.3 g mol^-1`. Therefore the molar mass of `Ba(NO_2)_2` is `229.3 g mol^-1`.

n = 4.50 moles
m = ?
M = 229.3 `g mol^-1`

Step 2, you can now find the mass of `Ba(NO_2)_2`. To find the mass, you need to multiply the number of moles (n) with molar mass (M), in other words, `m = n xx M`

`m = 4.50 xx 229.3 = 1031.85`

Therefore, there are 1031.85 grams in 4.50 moles of `Ba(NO_2)_2`.