Question

complete and balance the following redox equation. H2S + HNO3=> S+ NO (acidic solution)

Answer 1

First split the reaction in two parts as:

H2S ---------> S ------(1) and HNO3 ----------> NO    -------(2)

First balance eq (1) step by step as:

H2S ---------> S

H2S ---------> S + 2H+    (balance H)

H2S ---------> S + 2H+ + 2e- (balance charge) ---------(3)

Now, balance equation (2) as:

HNO3 ---------->   NO  

HNO3 ---------->   NO + 2H2O (balance O)      

HNO3 + 3H+ ---------->   NO + 2H2O   (balance H)

HNO3 + 3H+ + 3e- ---------->   NO + 2H2O --------------(4) (balance charge)

Now, multiply eq (3) by 3 as:

3H2S ---------> 3S + 6H+ + 6e- ----------(5)

and multiply eq (4) by 2 as:

2HNO3 + 6H+ + 6e- ----------> 2NO + 4H2O ---------(6)

Finally, add eq (5) and (6):   

3H2S +   2HNO3 + 6H+ + 6e- ----------> 3S + 6H+ + 6e- +   2NO + 4H2O

Now, cancell the electrons and common H+ on either side to get balanced equation:

3H2S +   2HNO3 ----------> 3S +   2NO + 4H2O