important question of redox reaction with answer for aieee 2010

Three reactions involvingH2PO-4 are given below :

(i) H3PO4

+ H2O ® H3O+ + H PO-

(ii) H PO-

+ H2O ® HPO2

- + H3O+



2

4

2

4

4



(iii) H2PO-4 + OH- ® H3PO4 + O2-


In which of the above does H2PO-4 act as an acid ?



(1) (ii) only



(2) (i) and (ii)

(3) (iii) only

(4) (i) only



(1)

















Sol :

(i)

H PO

4

+ H ® H O+ + H PO-









3

2

3

2

4









acid





conjugate base







(ii)

H PO-

+ H2O ® HPO-2



+ H O+









2

4



4



3









acid





conjugate base









(iii) H PO-

+ OH-

® H PO

4

+ O–2









2

4

acid

3











acid



conjugate acid





















Only in reaction (ii) H2PO-4 acids as ‘acid’.