Saved Bookmarks
| 1. |
Explain the uses of common ion effect. |
|
Answer» Solution :In PURIFICATION of NaCl : To remove the impurities of `Na_2SO_4 , MgSO_4` from NaCl solution HCl gas is passed in solution of NaCl so ppts of NaCl obtained by common ion effect. To separate soap from solution : Soap is a sodium salt of fatty acid if NaCl is added to solution of fatty acid `Na^+` ion is common ion so soap is separated as solid.  As `Na^+` is common ion so the REACTION PROCESSED in reverse direction and solid soap is separately . This is called salting process. In quantitatively analysis : if `K_(sp)` is less thancomplete precipitation is carried out. (i)For complete precipitation of `BaSO_4`excess `H_2SO_4` is added . (ii)For precipitation of `Ag^+` as AgCl excess NaCl is used. (iii) For precipitation of `Fe^(3+)` as `Fe(OH)_3` excess `OH^-` is maintain. (iv)In quantitatively analysis selective precipitation of reaction is carried on to by common ion effect. Qualitative analysis : In qualitative analysis `Ag^(+) , Hg^(+)` precipitate as chloride by HCl. e.g.-1 : In group II `Cu^(+2) , Cd^(2+)` have `K_(sp)` less for their precipitation `[S^(2-)]` must be less so HCl + `H_2S` is added . As a common ion effect of `H^+` the concentration of `S^(2-)` remain less and it is limited for CuS,CdS. e.-2 : In group III A `Fe^(2+) , Fe^(3+) , Al^(3+) , Cr^(3+)` ions are precipitation out as hydroxide. For that `OH^-` mustbe controlled so first `NH_4Cl` is added and than `NH_4OH` is added so as the common ion effect of `NH_4^+` the concentration of `[OH^-]` DECREASES so only IIIA precipitated. `[Q_(sp) gt K_(sp)]` . eg.-3 : Group-III B `Ni^(2+) , Co^(2+) , Zn^(2+), Mn^(2+) NH_4Cl, NH_4OH` and `H_2S` successful added so `NH_4^+` increase and `[OH^-]` decrease with that help `H^+` of `H_2S` increase and hence `[S^(2-)]`is more `Q_(sp) gt K_(sp)` sulphite of positive ion precipitated . (v) In drugs , cosmetic , fertilizers, by use of common ion effect pH is maintain . |
|