The only thing that remains is my NO2.

I have 100 grams of NO2.

Now, given the molar mass of NO2,

I can actually go from grams of NO2 to moles of NO2.

And so I use the molar mass,

putting the 46.01 grams on the bottom, so that my units will cancel out.

So now, I can cancel out grams of NO2 with grams of NO2.

If I stop my calculation at this point, I would have mols of NO2.

Which tells me how much I started with, but doesn't tell me anything about

the mass of HNO3, which is what is being asked for in the question.

So now, I need to use my mol to mol ratio.

Just as we did in the previous calculation,

where we were going from moles of one substance to moles of another.

I still have used by mass to get to moles.

Now I can put in my mole ratio.

Now I'm going to use the coefficients from my balanced equation, so I have 3 moles

of NO2, from the coefficient of 3 in my equation, on the bottom.

And I put that on the bottom, so

that moles of NO2 will cancel with moles of NO2.

On the top, I'm going to have 2 moles of HNO3,

because that's what I'm trying to find.

So now, moles of NO2 cancels with moles of NO2.

And if I stopped here, I'd have moles of HNO3 as my answer.

But I don't want moles of HNO3, I want grams of nitric acid or grams of HNO3.

So, I need to do one more step to get from moles of HNO3 to grams of HNO3.

And again, I'm going to use my molar mass, this time for the HNO3.

And I know 63.01 grams per mole of HNO3.

Now, my moles of HNO3 cancels with my moles of HNO3.

I check back over my units and

I see that the only units I have left remaining are grams of HNO3.