Which statement about the solubility of nitrates and ammonium salts is correct?

• A. Nitrates are insoluble but ammonium salts are soluble.
• B. Nitrates and ammonium salts are generally soluble in water.
• C. Both nitrates and ammonium salts react with water to form precipitates.
• D. Nitrates are soluble but ammonium salts are insoluble.

Answer: (B)

Solubility in water depends on whether the ions in a salt can be stabilized by hydration enough to overcome the solid’s lattice energy. Nitrates are practically always soluble because the NO3− ion forms strong hydration and, for typical cations, the lattice energy is not large enough to keep the solid intact. Ammonium salts behave similarly: the NH4+ ion is small and highly hydrated, and the lattice energies of these salts are generally overcome by hydration, so they dissolve readily. Because of these two tendencies, both nitrates and ammonium salts are regarded as generally soluble in water. The other statements would imply insolubility or reactivity with water, which isn’t the usual behavior for these salts under normal conditions.