Final answer:
HNO₃ decreases the solubility of Pb(OH)₂ in a saturated solution by providing additional H⁺ ions that react with OH⁻ ions to form water, illustrating the common ion effect and causing the equilibrium to shift and precipitate more Pb(OH)₂.
Step-by-step explanation:
Among the given substances, HNO₃ will decrease the solubility of Pb(OH)₂ in a saturated solution. This is because HNO₃ is a strong acid and will provide additional H⁺ ions when it dissociates in water. The added H⁺ ions will react with the hydroxide ions (OH⁻) from the saturated Pb(OH)₂ solution, forming water and thereby reducing the concentration of OH⁻ ions in solution.
The reaction can be represented as follows:
- HNO₃ (aq) → H⁺ (aq) + NO₃⁻ (aq)
- H⁺ (aq) + OH⁻ (aq) → H₂O (l)
This process is a classic example of the common ion effect, where adding an ion that is already present in the solution causes the equilibrium to shift, in this case, by precipitating more Pb(OH)₂, thus decreasing its solubility.
The other options such as NaNO₃, Pb(NO₃)₂, NaCl, and HCl do not decrease the solubility of Pb(OH)₂ in the same way. NaNO₃ and Pb(NO₃)₂ provide NO₃⁻ ions that do not affect the equilibrium significantly, as both Pb²⁺ and OH⁻ are still present. NaCl provides Na⁺ and Cl⁻ ions, which do not directly affect the dissolution equilibrium of Pb(OH)₂. While HCl also provides H⁺ ions, it also introduces Cl⁻ ions which will form a soluble complex with Pb²⁺, so its effect on Pb(OH)₂ solubility depends on the exact conditions of the reaction.