How do i find the mass in an impure substance

I have a .4230g sample of impure sodium nitrate.When it's heated, all of the sodium nitrate is converted to .1478g of sodium nitrite and oxygen gas. I need to find the percent of sodium nitrate in the original substance. As a hint, the problem asks me to find the mass of sodium nitrate in the impure substance, but I don't know how to do that.

The balanced equation in
2NaNO_3-----> 2NaNO_2+ O_2


Please explain how to do it.
I'm familiar with converting to moles and grams and whatnot, I just don't know where to start with this problem.

The balanced equation: 2NaNO3-----> 2NaNO2+ O2

The coefficients in the balanced equation determine the ratio of the moles of reactants to moles of products. According to the balanced equation, 2 moles of NaNO3 produce 2 moles of NaNO2 and 1 mole of O2.

The mole ratio of NaNO3 : NaNO2 = 1 : 1

Mass of 1 mole of NaNO3 = 23 + 14 + 48 = 85 g
Mass of 1 mole of NaNO2 = 23 + 14 + 32 = 69 g

Moles of NaNO2 = 0.1478 ÷ 69 = mole of NaNO3.
Mass of NaNO3 = moles * molar mass = (0.1478 ÷ 69) * 85 = 0.18207 g

% = 100 * (0.18207 ÷ 0.4230) = 43.04 %

All right, according to your balanced equation, starting material and product are in a 1:1 ratio.

So you have the number of grams of NaNO2 you obtain, and you convert that to the number of moles. And that number of moles equals the number of moles of NaNO3 in the material, so you can figure out how many grams that corresponds to. Then, compare that mass to the mass of the sample.