On mélange 100 mL d'une solution d'ammoniac NH3 2,0 M et 100 mL d'une solution de chlorure de

step 1 So the solubility product constant, this is denoted by KSP. And so we need to know the equation

On mélange 100 mL d'une solution d'ammoniac NH3 2,0 M et...

On mélange $100 \mathrm{~mL}$ d'une solution d'ammoniac $\mathrm{NH}_3 2,0 \mathrm{M}$ et $100 \mathrm{~mL}$ d'une solution de chlorure de magnésium $\mathrm{MgCl}_2 0,02 \mathrm{M}$. a) Quelle est la masse du précipité qui se forme ? b) Si on ajoute dans la solution contenant ce précipité du chlorure d'ammonium $\mathrm{NH}_4 \mathrm{Cl}$, on peut provoquer sa redissolution. Quelle masse minimale de chlorure d'ammonium solide faut-il y introduire pour que cette redissolution soit complète? c) Comment pourrait-on empêcher la formation d'un précipité d'hydroxyde lors du mélange des deux solutions?

On mélange $100 \mathrm{~mL}$ d'une solution d'ammoniac $\mathrm{NH}_3 2,0 \mathrm{M}$ et $100 \mathrm{~mL}$ d'une solution de chlorure de magnésium $\mathrm{MgCl}_2 0,02 \mathrm{M}$.
a) Quelle est la masse du précipité qui se forme ?
b) Si on ajoute dans la solution contenant ce précipité du chlorure d'ammonium $\mathrm{NH}_4 \mathrm{Cl}$, on peut provoquer sa redissolution. Quelle masse minimale de chlorure d'ammonium solide faut-il y introduire pour que cette redissolution soit complète?
c) Comment pourrait-on empêcher la formation d'un précipité d'hydroxyde lors du mélange des deux solutions?

Key Concepts

Precipitation Reaction

This concept deals with the formation of an insoluble solid when two soluble substances are mixed in aqueous solution. When ions combine to form a compound that exceeds its solubility, a precipitate forms. Understanding precipitation reactions is crucial in predicting whether certain compounds will remain in solution or separate as solids.

Solubility Product Constant (Ksp)

The solubility product constant quantifies the extent to which a compound can dissolve in water. It is the equilibrium constant for a sparingly soluble salt dissolving into its ions. By comparing the ionic product to the Ksp value, one can predict if a precipitate will form or if an existing solid will dissolve.

Limiting Reactant

In chemical reactions, the limiting reactant is the reactant that is completely consumed first, thus determining the maximum amount of product that can be formed. Recognizing the limiting reactant is essential in quantitative problems where the mass or moles of a precipitate are calculated.

Common Ion Effect

This effect occurs when a compound containing an ion already present in an equilibrium mixture is added, shifting the equilibrium position. In the context of solubility, adding a common ion can reduce the solubility of a sparingly soluble salt, or in some cases, its removal can enhance dissolution according to Le Chatelier's principle.

Equilibrium Shift / Le Chatelier's Principle

Le Chatelier’s principle explains how an equilibrium system responds to disturbances such as changes in concentration, pressure, or temperature. When an external species (like an added ion) perturbs the equilibrium, the system shifts to counteract the change, thereby affecting processes such as precipitation or redissolution.

Acid?Base Equilibrium

Many reactions, especially those involving weak bases like ammonia, are governed by acid?base equilibria. The equilibrium between ammonia and water, which produces hydroxide ions, is central to understanding how pH changes can influence the solubility of compounds like metal hydroxides.

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