Assume that you have an aqueous solution of an unknown salt. Treatment of the solution with dilute NaOH, Na2SO4, and KCl produces no precipitate. Which of the following cations might the solution contain? (a) Ag+ (b) Cs+ (c) Ba2+ (d) NH4 +

Verified step by step guidance

1. First, let's understand the concept of precipitation reactions. These are reactions that occur when two soluble salts in aqueous solution combine to form a salt that is insoluble in water, or a precipitate.
2. Next, let's consider the given information. The unknown salt does not form a precipitate when treated with NaOH, Na2SO4, and KCl. This means that the cation in the unknown salt does not form an insoluble compound with OH-, SO4^2-, or Cl- ions.
3. Let's analyze each of the given cations: (a) Ag+ would form a precipitate with Cl- (AgCl is insoluble in water), (b) Cs+ does not form a precipitate with any of the anions, (c) Ba2+ would form a precipitate with SO4^2- (BaSO4 is insoluble in water), and (d) NH4+ does not form a precipitate with any of the anions.
4. From the above analysis, we can see that the cations that do not form a precipitate with OH-, SO4^2-, or Cl- ions are Cs+ and NH4+.
5. Therefore, the unknown salt could contain either Cs+ or NH4+ cations.

Key Concepts

Solubility Rules

Solubility rules are guidelines that predict the solubility of various ionic compounds in water. For instance, most alkali metal salts, such as those containing Na+ or K+, are soluble, while certain cations like Ag+ and Ba2+ can form insoluble precipitates with specific anions. Understanding these rules helps determine which cations can remain in solution when treated with different reagents.

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble compound, or precipitate. The formation of a precipitate is indicated by cloudiness or solid formation in the solution. In this question, the absence of precipitate upon treatment with NaOH, Na2SO4, and KCl suggests that the cations present do not form insoluble compounds with these anions.

Common Cations and Their Behavior

Different cations exhibit distinct behaviors in aqueous solutions based on their chemical properties. For example, NH4+ is typically soluble and does not form precipitates with the tested reagents, while Ag+ can form precipitates with halides and hydroxides. Recognizing the behavior of common cations helps in predicting which ions can coexist in solution without forming precipitates.