Balancing Equations for Half-reactions Your laboratory instructor will assign a

Question

Balancing Equations for Half-reactions Your laboratory instructor will assign a number of die following equations for half-reactions to balance. Balance them on your own paper and submit them at the designated time. Identify each half-reaction as an oxidation or reduction. O_2 (g) rightarrow H_2 O(l) (acidic solution) H_2 S(aq) rightarrow S(s) (acidic solution) CIO^- (aq) rightarrow CI^- (aq) (acidic solution) NO_3^0 (aq) rightarrow NO_2^- (aq) (acidic solution) I^- (aq) rightarrow IO_3^- (aq) (acidic solution) VO^2+ (aq) rightarrow V^3 (aq) (acidic solution) Cr^3+ (aq) rightarrow CrO_4^2- (aq) (basic solution) CI_2 O_7 (g) rightarrow CIO_2^- (aq) (basic solution) C_2 H_5 OH (aq) rightarrow CH_3 COOH(aq) (basic solution) NO(g) rightarrow NO_3^- (aq) (basic solution) NO_2^- (aq) rightarrow N_2 O_2^2- (aq) (basic solution) SeO_3^2- (aq) rightarrow SeO_4^2- (aq) (basic solution)

Explanation / Answer

(1) O2 (g) ------------> H2O (l)             Reduction half reaction

(i) TO balance oxygens in acidic medium add H2O molecules.

O2   ----------> H2O + H2O

(ii) To balance hydrogens in acidic medium add H+ ions

O2   + 4 H+ ----------> 2 H2O

(iii) To balance charges add electrons

O2   + 4 H+ + 4 e ----------> 2 H2O

This is the balanced half reaction. It involves gaining of electrons, hence it is reducton half.

(2) Follow similar proceduce as above

(3) ClO- ----------> Cl-       

(i) To balance oxygens in basic medium add OH- ions.

ClO- ----------> Cl- + OH-

(ii) To balance hydrogens in basic medium add H2O molecules.

ClO- + H2O ----------> Cl- + 2 OH-

(iii) To balace charges add electrons

ClO- + H2O + 2 e ----------> Cl- + 2 OH-

This is the balanced half reaction. Since it involes in gain of electrons, it is a reduction half reaction.

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