9701 MCQ Solution 48

Question 48: [Physical > Electrochemistry]

When ammonia is converted into nitric acid on a commercial scale, the following reactions can occur.

In which reaction does the greatest change in oxidation of the nitrogen occur?

Reference: Past exam paper -June 2003 Paper 1 Q8

Solution 48:

Answer: A.

B the greatest change in oxidation number of nitrogen is from NO2 to NO , which is from +4 to +2. a reduction

C the greatest change in oxidation number of nitrogen is from NO to NO2 , which is from +2 to +4. an oxidation

D the greatest change in oxidation number of nitrogen is from NH3 to N2 , which is from -3 to 0. an oxidation

A is the answer because the greatest change in oxidation number of nitrogen is from NH3 to NO , which is from -3 to +2. an oxidation

in oxidation questions we don’t mind the number of moles of the molecule for example whether there were 2NH3 or 3NH3 the oxidation number of each atom will be calculated according to 1NH3 , and we don’t mind mind the number of atoms in the molecule when we are calculating the oxidation number of that particular atom,  for example whether it was NO2 or NO the oxidation number of oxygen is calculated as 1 atom , therefore the oxidation number of oxygen is -2. but the number of atoms in a molecule do matter for the other atoms if they were one for example. if it was NO then the oxidation number of nitrogen is +2 because there is one oxygen atom, but as for NO2 then the oxidation number of nitrogen is +4 , because there are 2 atoms of oxygen each gaining 2 electrons.