Question 4.5: IDENTIFYING PRECIPITATION REACTIONS When aqueous solutions o...
IDENTIFYING PRECIPITATION REACTIONS
When aqueous solutions of two ionic compounds are mixed, the following results are obtained. (Only the anion of the first compound, represented by blue spheres, and the cation of the second compound, represented by red spheres, are shown.) Which cations and anions, chosen from the following lists, are compatible with the observed results?
STRATEGY
The process represented in the drawing is a precipitation reaction because ions in solution drop to the bottom of the container in an ordered arrangement. Counting the spheres shows that the cation and anion react in equal numbers (8 of each), so they must have the same number of charges—either both singly charged or both doubly charged. (There is no triply charged cation in the list.) Look at all the possible combinations, and decide which would precipitate.
Possible combinations of singly charged ions: AgNO_{3}, KNO_{3}, AgCl, KCl
Possible combinations of doubly charged ions: CaCO_{3}, CdCO_{3}
Of the possible combinations, AgCl, CaCO_{3}, and CdCO_{3} are insoluble, so the anion might be Cl^{-} or CO^{2-}_{3} and the cation might be Ag^{+},Ca^{2+} , or Cd^{2+}.