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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 71d

Ignoring protolysis reactions, indicate the concentration of each ion or molecule present in the following solutions: (d) a mixture of 45.0 mL of 0.272 M NaCl and 65.0 mL of 0.0247 M (NH4)2CO3. Assume that the volumes are additive.

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1
Calculate the total volume of the solution by adding the volumes of the NaCl and (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> solutions. This is done by adding 45.0 mL and 65.0 mL.
Calculate the moles of NaCl initially present using its concentration and the volume of the NaCl solution. Use the formula: moles = concentration (M) imes volume (L).
Calculate the moles of (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> initially present using its concentration and the volume of the (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> solution. Use the same formula as in step 2.
Determine the concentration of each ion in the final solution. For NaCl, which dissociates into Na<sup>+</sup> and Cl<sup>-</sup>, the concentration of each ion is equal to the total moles of NaCl divided by the total volume of the solution. For (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub>, which dissociates into 2NH<sub>4</sub><sup>+</sup> and CO<sub>3</sub><sup>2-</sup>, the concentration of NH<sub>4</sub><sup>+</sup> is twice the moles of (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> divided by the total volume, and the concentration of CO<sub>3</sub><sup>2-</sup> is equal to the moles of (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> divided by the total volume.
Summarize the concentrations of Na<sup>+</sup>, Cl<sup>-</sup>, NH<sub>4</sub><sup>+</sup>, and CO<sub>3</sub><sup>2-</sup> in the final solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Concentration and Molarity

Concentration refers to the amount of solute present in a given volume of solution, commonly expressed in molarity (M), which is moles of solute per liter of solution. Understanding how to calculate molarity is essential for determining the concentration of ions or molecules in a mixture.
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Molarity Concept

Dilution and Mixing Solutions

When two solutions are mixed, the total volume increases, and the concentrations of the solutes change. The final concentration can be calculated using the formula C1V1 + C2V2 = CfinalVfinal, where C is concentration and V is volume. This principle is crucial for accurately determining the concentrations of ions in the resulting solution.
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Solution Dilution Process

Ionic Dissociation

Ionic compounds, such as NaCl, dissociate into their constituent ions when dissolved in water. For example, NaCl dissociates into Na⁺ and Cl⁻ ions. Understanding how different compounds dissociate is vital for calculating the concentrations of individual ions in a mixed solution.
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