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

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#.