[eeyore1228]

I am needing help on a problem.  

A solution is prepared by adding 15.0 g of nitric acid to water and diluting the solution to 500.0 mL (total solution volume)
What is the Molarity of the nitrate ion?

I know that if you were getting the Molarity of nitric acid it would be

15g HNO3 x (1 mole HNO3/63g HNO3) = 0.238 M HNO3

but if you are only needing the Molarity of the nitrate ion, would you use 15g NO3- in your equation, or something different?

[Mitch]

Yes you would. An esoteric step would be to make the ratio that 1 mol of HNO₃ = 1 mol of NO₃^-.