Final answer:
The molar solubility of magnesium fluoride will decrease when dissolved in a solution that contains a common ion like magnesium from magnesium nitrate due to the common ion effect, which causes the system to shift equilibrium to maintain the Ksp.
Step-by-step explanation:
The molar solubility of magnesium fluoride (MgF2) in water is given as 2.3 x 10−4 molar. When MgF2 is dissolved in a 0.100 M solution of magnesium nitrate, the solubility will change due to the common ion effect. The presence of an additional source of Mg2+ ions from magnesium nitrate will reduce the solubility of MgF2 because the product of the concentrations of the ions will reach the solubility product constant (Ksp) before the same amount of MgF2 has dissolved in comparison to pure water.
According to the Le Châtelier's principle, if a system at equilibrium is disturbed by a change in concentration, temperature, volume, or pressure, the system will shift its equilibrium position to counteract the effect of the disturbance. In this case, the system will shift to the left, causing less MgF2 to dissolve in order to maintain the equilibrium constant, reducing its solubility.
This phenomenon is a pivotal concept in solubility equilibria, and understanding the effect of the common ion on solubility is crucial when predicting the solubility of ionic compounds under various conditions. It's important to consider both the initial and final states of the ionic concentrations when determining how the solubility will be affected.