Q62 / 180 · NEET 2015 (Phase 1) · Chemistry

The Ksp of Ag2CrO4, AgCl, AgBr and AgI are respectively, 1.1×10-12 , 1.8×10-10 , 5.0×10-13 , 8.3×10-17 . Which one of the following salts will precipitate last if AgNO3 solution is added to the solution containing equal moles of NaCl, NaI, NaBr and Na2CrO4 ?

  • A
    AgI
  • B
    AgCl
  • C
    AgBr
  • Correct answer
    D
    Ag2CrO4

Solution

For, Ag 2 CrO 4 ⇌ 2Ag + +CrO 4 2-
solubility product
K sp = ( 25 ) 2 ×5=4s 3
K sp =( 1.1× 10 −12 )
S=3 K sp 4 =0.65× 10 −4
For, AgCl⇌ Ag + +Cl -
K sp =S×S   ( K sp =1.8× 10 −10 )
S= K sp =1.34× 10 −5
For, AgBr⇌ Ag + +Br -
K sp =S×S ( K sp =5×10 -13 )
S= K sp =0.71× 10 −6
For, AgI⇌ Ag + +I -
K sp =S×S ( K sp =8 .3×10 -17 )
S= K sp =0.9× 10 −8
therefore, the solubility of A g 2 Cr O 4 is highest so it is precipitate last.

Hence, the correct answer is option: 'D'.

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