On mélange 200 mL d'une solution de chlorure de sodium NaCl ( c=146,25 g. L^-1 ) et 300 mL de

step 1 All right, so we've got some potassium chloride. Let's find out how many moles of each ion we're

On mélange 200 mL d'une solution de chlorure de sodium NaCl...

On mélange $200 \mathrm{~mL}$ d'une solution de chlorure de sodium $\mathrm{NaCl}$ ( $\mathrm{c}=146,25$ g. $\mathrm{L}^{-1}$ ) et $300 \mathrm{~mL}$ de solution de chlorure de potassium $\mathrm{KCl}\left(\mathrm{c}=37,25 \mathrm{~g} . \mathrm{L}^{-1}\right)$. Quelles sont les concentrations molaires $\mathrm{c}\left(\mathrm{Na}^{+}\right), \mathrm{c}\left(\mathrm{K}^{+}\right), \mathrm{c}\left(\mathrm{Cl}^{-}\right)$dans le mélange? (Dans leurs solutions, $\mathrm{NaCl}$ et $\mathrm{KCl}$ sont entièrement dissociés en ions $\left.\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{C}^{-}\right)$.

Key Concepts

Molarity Calculation

Molarity is defined as the number of moles of solute per liter of solution. After determining the amount of moles (using conversion from mass concentration) and summing the volumes of the combined solutions, the final molar concentration is obtained by dividing the total number of moles by the total volume. This calculation is critical in many aspects of solution chemistry including reaction stoichiometry and chemical equilibrium.

Solution Mixing and Dilution

When two or more solutions are combined, the total volume of the mixture changes, and the moles of solute are distributed over the new volume. Calculating the final concentration requires accounting for the dilution effect. This principle is fundamental when combining different solutions and is used to determine the new molar concentrations of solutes.

Ionic Dissociation

This concept involves understanding that many ionic compounds dissolve in water by separating into their constituent ions. In a fully dissociated electrolyte, each formula unit yields a specific, stoichiometrically determined number of each ion. Recognizing the dissociation behavior is essential for computing the concentrations of individual ions in a solution.

Mass Concentration to Molarity Conversion

Mass concentration (given in grams per liter) provides the mass of solute per volume of solution. Converting this to molarity involves using the molar mass of the solute to determine the number of moles present. This step is critical for quantifying the amount of substance in moles, which is necessary for stoichiometric calculations.

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