Question

Which of these ion pairs can simultaneously exist in solution without undergoing a redox reaction?

1) Na⁰ (s) & Mg²⁺

^{2) Na+ & Mg (s)}

^{3) Al & MnO₄-}

^{4) Zn 2+ & NO}

Answer 1

1)

E^o_red of Na⁺/Na = - 2.71 V

E^o_red of Mg²⁺/Mg = - 2.37 V

So, Mg²⁺ can oxidise Na^{​​​​​​} .

2 Na + Mg²⁺$\to$ 2Na⁺ + 2Mg

E^o_cell = E^o_red (Mg|Mg⁺) - E^o_red(Na⁺|Na) = -2.37 - (-2.71) V

= 0.34 V.

So, redox reaction between Na(s) and Mg²⁺ feasible

2)

As standard reduction potential of Na⁺|Na couple is less than that of Mg²⁺|Mg , there is no redox reaction between Na⁺ and Mg(s).

3)

Standard reduction potential of Al³⁺|Al = - 1.66 V and

MnO₄^-|Mn²⁺ = 1.51 V.

so, MnO₄ ^- can oxidise Al to Al³⁺. So redox reaction is posible.

4)

E^o_red of Zn²⁺|Zn = - 0.76 V

E^o_red of NO₃^-|NO = 0.96 V.

Therefore NO can not reduce Zn²⁺ , hence there will be no redox reaction.

Hence, the ion pairs can exist in solution simultaneously without undergoing a redox reaction are given below.

2) Na⁺ and Mg

4) Zn²⁺ and NO.