Question

. In which reaction is nitric acid acting as an oxidising agent?

A. CuO + 2HNO3 → Cu(NO3)2 + H2O
B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2
C. Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2
D. NaOH + HNO3 → NaNO3 + H2O. In which reaction is nitric acid acting as an oxidising agent?
A. CuO + 2HNO3 → Cu(NO3)2 + H2O
B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2
C. Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2
D. NaOH + HNO3 → NaNO3 + H2O

Answer 1

B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2

Step-by-step explanation:

A substance is acting as oxidising agent when is reducing its chemical state in the reaction.

In HNO3, Nitrogen has an oxidation state of +5 (Each oxygen is -2, 3 oxygens, -6, 1 hydrogen, +1). Thus, if the oxidation state of the nitrogen in the products is < +5, the nitrogen is reducing its oxidation state acting as oxidising agent.

In the reactions:

A. CuO + 2HNO3 → Cu(NO3)2 + H2O . In Cu(NO₃)₂, Nitrogen has an oxidation state of +5. Thus, nitric acid is not acting as oxidising agent.

B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2 . Also, oxidation state in Cu(NO₃)₂ does not have any change but there is another product, NO₂, where nitrogen has an oxidation state of +4. That means nitric acid is acting as oxidising agent.

C. Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2 . Here, in NaNO₃, oxidation state of nitrogen is +5 (Na: +1, 3 O: -6). Thus, nitrogen is not changing is oxidation state and nitric acid is not acting as oxidising agent.

D. NaOH + HNO3 → NaNO3 + H2O. Here, also, the product is NaNO₃. That means nitric acid is not acting as oxidising agent.

Answer 2

B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2

Step-by-step explanation:

Hello,

In this case, we should understand oxidizing agents as those substances able to increase the oxidation state of another substance, therefore, in B. reaction we notice that copper oxidation state at the beginning is zero (no bonds are formed) and once it reacts with nitric acid, its oxidation states raises to +2 in copper (II) nitrate, thus, in B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2 nitritc acid is acting as the oxidizing agent.

Moreover, in the other reactions, copper (A.), sodium (C. and D.) remain with the same initial oxidation state, +2 and +1 respectively.

Regards.