If a 40 g sample of NaCl is composed of 39.34% Sodium, how many grams of
that sample are Sodium?

15.7g

Explanation:

mass percent=mass of element/mass of compound *100

39.34=unknown(x)/40g×100

39.34=5x/2

multiplying both sides by 2,we get

5x=78.68

devide by 5 on both sides

x=15.74g Na

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !