La solubilité du sulfate de calcium CaSO4 est de 4,90 ·10^-3 mol. L^-1. A) On introduit 500 mg d

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La solubilité du sulfate de calcium CaSO4 est de 4,90 ·10^-3...

La solubilité du sulfate de calcium $\mathrm{CaSO}_4$ est de $4,90 \cdot 10^{-3}$ mol. $\mathrm{L}^{-1}$. A) On introduit $500 \mathrm{mg}$ de sulfate de calcium dans un litre d'eau ; a. Quelle est la concentration molaire des ions $\mathrm{Ca}^{2+}$ et $\mathrm{SO}_4{ }^{2-}$ dans la solution? b. Le produit de ces deux concentrations donne-il la valeur du produit de solubilité du sulfate de calcium? c. Que deviennent ces concentrations, si l'on ajoute à la solution 1 litre d'eau pure? B) Les réponses à ces trois questions sont-elles les mêmes que précédemment si l'on introduit dans 1 litre d'eau, a. $666 \mathrm{mg}$ de sulfate de calcium? b. $1,50 \mathrm{~g}$ de sulfate de calcium ? c. $1,00 \mathrm{~g}$ de sulfate de calcium ? C) Quelle est la quantité d'eau minimale nécessaire pour dissoudre $1,00 \mathrm{~g}$ de sulfate de calcium?

La solubilité du sulfate de calcium $\mathrm{CaSO}_4$ est de $4,90 \cdot 10^{-3}$ mol. $\mathrm{L}^{-1}$.
A) On introduit $500 \mathrm{mg}$ de sulfate de calcium dans un litre d'eau ;
a. Quelle est la concentration molaire des ions $\mathrm{Ca}^{2+}$ et $\mathrm{SO}_4{ }^{2-}$ dans la solution?
b. Le produit de ces deux concentrations donne-il la valeur du produit de solubilité du sulfate de calcium?
c. Que deviennent ces concentrations, si l'on ajoute à la solution 1 litre d'eau pure?
B) Les réponses à ces trois questions sont-elles les mêmes que précédemment si l'on introduit dans 1 litre d'eau,
a. $666 \mathrm{mg}$ de sulfate de calcium?
b. $1,50 \mathrm{~g}$ de sulfate de calcium ?
c. $1,00 \mathrm{~g}$ de sulfate de calcium ?
C) Quelle est la quantité d'eau minimale nécessaire pour dissoudre $1,00 \mathrm{~g}$ de sulfate de calcium?

Key Concepts

Stoichiometric Conversions

Stoichiometric conversions are critical in determining molar amounts from given masses of a substance, which then allows for the calculation of concentrations in solution. This concept involves using the molar mass of the compound to convert grams to moles, enabling further analysis of chemical equilibria like the solubility product.

Dilution Effects on Concentration

Dilution involves adding more solvent to a solution, which decreases the concentration of the solute without changing the number of moles present. In systems at equilibrium, such as saturated solutions, dilution can shift the balance if additional dissolved substance is available to reach the solubility limit again, while also affecting the apparent ion concentrations.

Chemical Equilibrium in Saturated Solutions

Chemical equilibrium in the context of sparingly soluble salts is reached when the rate of dissolution equals the rate of precipitation. At this point, the concentrations of the ions in solution remain constant, and the product of these concentrations equals the solubility product constant (Ksp). This balance is essential for understanding the behavior of the salt under various conditions, such as changes in volume or the addition of extra solute.

Solubility

Solubility refers to the maximum amount of a substance that can dissolve in a given quantity of solvent at a specified temperature to form a homogeneous solution. In the context of sparingly soluble salts, the measured solubility indicates the limit at which the substance dissolves before reaching a saturation point where additional solute will not dissolve under those conditions.

Molar Concentration

Molar concentration, typically expressed in moles per liter (M), is a measure of the amount of solute present in a given volume of solution. It is a key factor when analyzing chemical reactions in solution since it directly affects reaction rates, equilibrium positions, and the evaluation of the solubility product of sparingly soluble salts.

Solubility Product Constant (Ksp)

The solubility product constant, or Ksp, is an equilibrium constant that applies to the dissolution of a sparingly soluble salt. It is defined as the product of the molar concentrations of the constituent ions, each raised to the power of their stoichiometric coefficients. Ksp provides a quantitative measure of the extent to which a salt can dissolve in water before reaching equilibrium.

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