Question

(iii) The metal oxide which cannot be reduced by hydrogen is (sodium oxide, copper oxide).
(iv) A metal nitrate which leaves no residue on heating is (Potassium nitrate, Ammonium nitrate).

Answer 1

sodium oxide cannot be reduced by hydrogen becoz sodium is more reactive than hydrogen
potassium nitrate doesn't  give any residue on heating

Answer 2

Answer:

For (iii): The correct answer is Sodium oxide.

For (iv): The correct answer is Ammonium nitrate.

Explanation:

• For (iii):

When a metal oxide reacts with hydrogen, hydrogen will replace the metal which is less reactive than hydrogen. The reactivity of metals is judged from the reactivity series.

In this series, the metals lying above hydrogen atom are more reactive and will easily and the metals lying below the hydrogen atom are less reactive.

From the oxides given, hydrogen can easily replace copper from its oxide because hydrogen is more reactive than copper. The reaction between the two follows the equation:

$CuO+H_2\rightarrow H_2O+Cu$

$NaO+H_2\rightarrow \text{No reaction}$

Therefore, the correct answer is Sodium oxide.

• For (iv):

Equation for the heating of potassium nitrate follows:

$4KNO_3(s)\rightarrow 2K_2O(s)+2N_2(g)+5O_2(g)$

By Stoichiometry of the reaction:

4 moles of potassium nitrate produces 2 moles of potassium oxide solid (pale yellow) , 2 moles of nitrogen gas and 5 moles of oxygen gas.

Equation for the heating of ammonium nitrate follows:

$NH_4NO_3(s)\rightarrow N_2O(g)+2H_2O(l)$

By Stoichiometry of the reaction:

1 mole of ammonium nitrate produces 1 mole of nitrous oxide gas and 2 moles of water.

From the above reactions, heating of potassium nitrate is giving residue.

Therefore, the correct answer is ammonium nitrate.