Question

A solution is 0.022 M Ca(NO3)₂ and 0.005M AgC₂H₃O₂. K₂CO₃ is chosen in a fractional precipitation experiment.

A) Which ion will precipitate out first?

B) What is the minimum K₂CO₃ concentraion required to trigger the precipitation of the first ion?

C) What % of the first ion has been removed by the time the second ion starts to precipitate?

Answer 1

A) Ca2+ ion precipitate first

B) The answer is 1.50×10^-7M

Explanation

Concentration of Ca(NO3)2 = 0.022M

Concentration of Ca2+ = 0.022M

   Ksp of CaCO3 = 3.3×10^-9

Ksp = [Ca2+] × [ CO32-]

Therefore,

( 0.022) × [ CO32-] = 3.3×10^-9

[ CO32- ] = 1.50×10^-7M

C) The answer is 55.64%

Explanation

Ksp of Ag2CO3 = 8.46×10^-7

[ Ag+] = 0.0050M

[ Ag+ ]^2 × [ CO32-] = 8.46 ×10^-12

(0.0050 )^2 × [ CO32- ] = 8.46×10^-12

   [ CO32-] = 3.38×10^-7M

when , [ CO32- ] is 3.38×10^-7M concentration of Ca2+ calculated as

   [ Ca2+ ]× [ CO32- ] = 3.3×10^-9

   [Ca2+ ]× ( 3.38×10^-7) = 3.38×10^-9

   [ Ca2+] = 3.3×10^-9/3.38×10^-7

   = 9.76×10^-3M

   Initial concentration of Ca2+ = 0.022M

Concentration of Ca2+ when Ag+ start precipitate = 0.00976M

Concentration of Ca2+ removed = 0.022M - 0.00976M= 0.01224M

  % Ca2+ removed = (0.01224/0.022)×100 = 55.64%