Barium nitrate is added to a solution of 0.025 M sodium...

Barium nitrate is added to a solution of $0.025 M$ sodium fluoride. (a) At what concentration of $\mathrm{Ba}^{2+}$ does a precipitate start to form? (b) Enough barium nitrate is added to make $\left[\mathrm{Ba}^{2+}\right]=0.0045 \mathrm{M}$. What percentage of the original fluoride ion has precipitated?

Barium nitrate is added to a solution of $0.025 M$ sodium fluoride.
(a) At what concentration of $\mathrm{Ba}^{2+}$ does a precipitate start to form?
(b) Enough barium nitrate is added to make $\left[\mathrm{Ba}^{2+}\right]=0.0045 \mathrm{M}$. What percentage of the original fluoride ion has precipitated?

Key Concepts

Common Ion Effect

The common ion effect is the phenomenon where the presence of an ion, which is common to two different compounds in solution, reduces the solubility of a sparingly soluble salt. This occurs because the added ion shifts the equilibrium according to Le Chatelier's principle, thereby decreasing the concentration of one of the ions produced by the salt and affecting the onset of precipitation.

Solubility Product Constant (Ksp)

The solubility product constant is a measure of the maximum product of the concentrations of the constituent ions of a sparingly soluble salt that can be present in a solution at equilibrium before precipitation occurs. It is used to predict when a solution becomes saturated and a solid will start to precipitate, based on the comparison of the ion product to the Ksp value.

Precipitation Equilibrium

Precipitation equilibrium describes the state in which a sparingly soluble salt is in dynamic balance with its dissolved ions in solution. At this equilibrium, the ion concentrations maintain a constant relationship as dictated by the Ksp, such that any further change in ion concentration can tip the system towards either further dissolution or precipitation.

Reaction Stoichiometry

Reaction stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. In the context of precipitation reactions, it ensures that the molar ratios of the ions required to form the precipitate are correctly accounted for, allowing calculation of the amounts of each ion that will react and determining the conditions at which precipitation commences.

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