How is a sodium ion and a sodium atom differ in mass if at all?

Ions have charge, whilst atom is neutral. 

For instance, Na+ has one electron less than a sodium atom.

So, sodium atom is 9.10938356 × 10^-31 kilograms heavier than sodium ion, which in reality, there is no difference 

Since there is the same amount of agn03 in both silver chloride and silver nitrate they produce the same amount of moles. therefore silver chloride produces the same amount of silver nitrate, so your answer is 15.0 moles of silver nitrate. i hope this !