Question 3(2009)
Give one test each to distinguish between the following pairs of chemical solutions:
(i) ZnSO4 and ZnCl2
(ii) FeCl2 and FeCl3
(iii) Calcium nitrate soln. and Calcium chloride soln.
(i) When BaCl2 soln. is added to ZnSO4, a white ppt. of BaSO4 is formed, whereas, no ppt. is formed in case of ZnCl2. Hence, the two solns. can be distinguished.
BaCl2 + ZnSO4 ⟶ BaSO4 ↓ [white ppt.] + ZnCl2
BaCl2 + ZnCl2 ⟶ No white ppt.
(ii) When NaOH soln. is added to the given solns., FeCl2 reacts to form a dirty green ppt. of Fe(OH)2 whereas, FeCl3 reacts to form a reddish brown ppt. of Fe(OH)3.
(iii) Add silver nitrate soln. to the given solns., calcium chloride reacts to form a white ppt. which is soluble in NH4OH and insoluble in dil. HNO3. The other soln. is calcium nitrate.
CaCl2 + 2AgNO3 ⟶ 2AgCl ↓ [white ppt.] + Ca(NO3)2
Ca(NO3)2 + AgNO3 ⟶ no white ppt.