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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 71a,b,c

Indicate the concentration of each ion or molecule present in the following solutions: (a) 0.35 M K3PO4 (b) 1.3×10−2 M MgSO4 (c) 0.0184 M CH3CH2OH

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Identify the dissociation equation for MgSO_4 in water: MgSO_4 (aq) \rightarrow Mg^{2+} (aq) + SO_4^{2-} (aq).
Recognize that MgSO_4 is a strong electrolyte, meaning it dissociates completely in solution.
Determine the initial concentration of MgSO_4, which is given as 1.3 \times 10^{-2} \text{ M}.
Since MgSO_4 dissociates completely, the concentration of Mg^{2+} ions will be equal to the initial concentration of MgSO_4, which is 1.3 \times 10^{-2} \text{ M}.
Similarly, the concentration of SO_4^{2-} ions will also be equal to the initial concentration of MgSO_4, which is 1.3 \times 10^{-2} \text{ M}.

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Key Concepts

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

Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. It is commonly used in chemistry to express the concentration of ionic compounds and other solutes in a solution. In the given question, the molarity of MgSO4 indicates how many moles of magnesium sulfate are present in one liter of solution.
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Dissociation of Ionic Compounds

Ionic compounds, such as magnesium sulfate (MgSO4), dissociate into their constituent ions when dissolved in water. For MgSO4, it dissociates into one magnesium ion (Mg²⁺) and one sulfate ion (SO4²⁻). Understanding this dissociation is crucial for determining the concentration of each ion in the solution based on the initial molarity of the compound.
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Stoichiometry of Dissociation

Stoichiometry refers to the quantitative relationship between reactants and products in a chemical reaction. In the context of dissociation, it allows us to calculate the concentration of each ion produced from a given molarity of an ionic compound. For example, from 1.3×10⁻² M MgSO4, we can deduce that the concentration of Mg²⁺ and SO4²⁻ ions will each be 1.3×10⁻² M, reflecting the 1:1 ratio of dissociation.
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