In the reaction between dilute nitric acid and magnesium metal, (a) how many moles of `HNO_(3)` reacts with a gram atom of metal? and (b) how many moles of `HNO_(3)` is oxidised by a gram atom of metal? 

Explanation

The skeleton equation is
`Mh+HNO_(3)rarrMg(NO_(3))_(2)+H_(2)O`
 The balanced equation is
`4Mg+10HNO_(3)rarr 4Mg(NO_(3))_(2)+NH_(4)NO_(3)+3H_(2)O`
a) Number of moles of `HNO_(3)` that reacts with a gram atom of `Mg = 10//4 = 2.5`
b) `NO_(3)^(-)` is a spectator ion. It is neglected in the equation.
`4Mg+NO_(3)^(-)+10H^(+)rarr4Mg^(2+)+NH_(4)^(+)+3H_(2)O`
Number of moles of `HNO_(3)^(-)` that is reduced by a gram atom of `Mg = 0.25`