Assume that you have an aqueous solution of an unknown salt. Treatment of the solution with dilute BaCl2, AgNO3, and Cu(NO3)2 produces no precipitate. Which of the following anions might the solution contain? (a) Cl- (b) NO3 (c) OH- (d) SO4- 2-

Verified step by step guidance

1. First, let's understand the concept of precipitation reactions. These are reactions in which two soluble salts in aqueous solution combine to form an insoluble salt, the precipitate.
2. Next, we need to know which salts are formed when the anions Cl-, NO3-, OH-, and SO4^2- react with Ba^2+, Ag^+, and Cu^2+. These are BaCl2, AgCl, CuCl, Ba(NO3)2, AgNO3, Cu(NO3)2, Ba(OH)2, AgOH, Cu(OH)2, BaSO4, Ag2SO4, and CuSO4.
3. Then, we need to know which of these salts are soluble and which are insoluble in water. BaCl2, AgCl, CuCl, Ba(NO3)2, AgNO3, Cu(NO3)2, Ba(OH)2, and Cu(OH)2 are soluble. AgOH, BaSO4, Ag2SO4, and CuSO4 are insoluble.
4. Since the treatment of the solution with BaCl2, AgNO3, and Cu(NO3)2 produces no precipitate, the anions Cl-, OH-, and SO4^2- can be ruled out because they form insoluble salts with at least one of the cations Ba^2+, Ag^+, and Cu^2+.
5. Finally, the only anion left is NO3-, which forms soluble salts with all three cations. Therefore, the solution might contain the anion NO3-.

Key Concepts

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble compound, known as a precipitate. The formation of a precipitate is determined by the solubility rules, which dictate whether certain combinations of ions will remain dissolved or form a solid. In this case, the lack of precipitate upon adding BaCl2, AgNO3, and Cu(NO3)2 suggests that the anions present do not form insoluble salts with the cations from these reagents.

Solubility Rules

Solubility rules are guidelines that help predict whether a compound will dissolve in water. For example, most chlorides are soluble except for those of silver, lead, and mercury, while sulfates are generally soluble except for those of barium, lead, and calcium. Understanding these rules is crucial for determining which anions can coexist in solution without forming precipitates when treated with specific cations.

Common Anions and Their Behavior

Common anions such as chloride (Cl-), nitrate (NO3-), hydroxide (OH-), and sulfate (SO4^2-) exhibit distinct behaviors in aqueous solutions. Nitrate is always soluble, while chloride and sulfate can form precipitates with certain cations. Hydroxide is generally insoluble with many cations, particularly transition metals. Recognizing the solubility of these anions in the context of the provided reagents is essential for identifying which anions could be present in the unknown salt solution.