Why can't nitrate ion in aluminium nitrate solution oxidise copper when a copper spoon is used to stir the solution?
Minor correction: It is not the spectrochemical series but rather the electrode potential tables. Those tabulated values are given under standard conditions
You are indeed correct in thinking that nitrate ion should oxidize copper. It is a game of pH. If you have very low pH and nitrate ions, the following reaction takes place (in the absence of other ions)...
$$\ce{Cu(s) + 4 HNO3(aq) -&gt; Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l)}$$