Question

You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃, ZnCl₂ and water. In which of the above containers, can these solutions be kept?

Answer 1

1. Solutions to be kept in a copper container:
   1. Dilute HCl can be kept since no chemical reaction is expected. Copper is placed below hydrogen in the activity series.
   2. Dilute HNO₃ cannot be kept since a chemical reaction is expected. Nitric acid is a strong oxidising agent.
      \[\ce{3Cu_{(s)} + 8HNO_3_{(dil)} -> 3Cu(NO3)2_{(aq)} + 2NO_{(g)} + 4H2O_{(aq)}}\]
   3. ZnCl₂ solution can be kept since copper is placed below zinc in the activity series and no chemical reaction is possible.
   4. Water can be kept since no chemical reaction is expected.
2. Solutions to be kept in an aluminium container:
   1. Dilute HCl cannot be kept since aluminium reacts with acid to evolve hydrogen gas.
      \[\ce{2Al_{(s)} + 6HCl_{(aq)} -> 2AlCl3_{(aq)} + 3H2_{(g)}}\] 
   2. Dilute HNO₃ can be kept. Actually, aluminium is initially oxidised by the acid to aluminium oxide (Al₂O₃). A coating of aluminium oxide gets deposited on the surface of the metal and makes it passive towards reaction with the acid.
   3. ZnCl₂ solution cannot be kept since a chemical reaction will take place as aluminium is placed above zinc in the activity series.
      \[\ce{2Al_{(s)} + 3ZnCl2_{(aq)} -> 2AlCl3_{(aq)} + 3Zn_{(s)}}\]
   4. You can store water as such in the container. However, we cannot keep steam since a chemical reaction is likely to take place.
      \[\ce{2Al_{(s)} + 3H2O_{(g)} -> Al2O3_{(s)} + 3H2_{(g)}}\]