calculate the percent composition, by mass, of carbon in Na2CO3. please explain how you get the answer.

%C = (mass C/total mass)*100 = ??

Just like any percent problem, it's the mass of the part you want over the total mass.
mass C = about 12
mass Na2CO3 = about 106 or so.
Where did those numbers come from? From the periodic table.

Are you implying that (12/106)*100 = 45.8%. No way. How do you get 45.8?

To calculate the percent composition by mass of carbon in Na2CO3 (sodium carbonate), you need to determine the total mass of the compound and the mass of carbon within it. Here's how you can do it:

1. Determine the molar mass of Na2CO3:
- The atomic masses of Na, C, and O are 22.99 g/mol, 12.01 g/mol, and 16.00 g/mol, respectively.
- Since there are two sodium atoms (Na2), one carbon atom (C), and three oxygen atoms (O3), the molar mass of Na2CO3 is:
molar mass(Na2CO3) = 2(atomic mass of Na) + (atomic mass of C) + 3(atomic mass of O)

2. Calculate the mass of carbon (C):
- The molar mass of carbon is 12.01 g/mol, which means that one mole of C weighs 12.01 grams.
- From the chemical formula, we know that there is one mole of carbon in one mole of Na2CO3.
- Therefore, the mass of carbon in Na2CO3 is equal to its molar mass, which is 12.01 grams.

3. Calculate the percent composition:
- The percent composition is determined by dividing the mass of carbon by the total mass of Na2CO3 and multiplying the result by 100.
- In this case: percent composition = (mass of C / mass of Na2CO3) × 100
- Substitute the values: percent composition = (12.01 g / molar mass(Na2CO3)) × 100

Now, you can substitute the values into the equation to calculate the percent composition of carbon in Na2CO3.

i got 45.8.