percent composition...?

Question

what is the percent composition of sodium carbonate?

Answer 1

I'm guessing you mean the percent composition by mass. If you mean otherwise, please tell me.
Very first thing you have to do is find the molar mass.
Molar Mass Na2CO3 = 2* 22.99 g/mol + 12.01 g/mol + 3*16.00 g/mol
= 105.99g/mol
So... lets just pretend that we have 1 mol of Na2CO3 That will make life easier.
So now we have 105.99g of Na2CO3
If we take each element's weight and multiply it by the times it appears in the formula we get that...
45.98 g of this will be sodium
12.01g of this will be carbon
48.00g of this will be oxygen.
So for percent compositions:
Percent composition = mass of element/mass of sample*100%
Sodium = 45.98g/105.99g * 100% = 43.48%
Carbon = 12.01g/105.99g * 100% = 11.33%
Oxygen = 48.00g/105.99g * 100% = 45.28%
If we add all of these together we get 100.00%

Answer 2

Percent comp is calculated by getting the masses of each individual atom, and then add all the masses together. Percent is simply (part/whole)*100

Use your periodic table to get atomic masses of sodium, carbon and oxygen. Google or look up the formula for carbonate to get correct formula.

Divide sodium mass by total mass and multiply by 100. Then do this for C and for O.