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Ch.4 - Chemical Quantities & Aqueous Reactions
Chapter 4, Problem 65

Consider the precipitation reaction: 2 Na3PO4(aq) + 3 CuCl2(aq) → Cu3(PO4)2(s) + 6 NaCl(aq). What volume of 0.175 M Na3PO4 solution is necessary to completely react with 95.4 mL of 0.102 M CuCl2?

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1
Identify the balanced chemical equation: \(2 \text{Na}_3\text{PO}_4(aq) + 3 \text{CuCl}_2(aq) \rightarrow \text{Cu}_3(\text{PO}_4)_2(s) + 6 \text{NaCl}(aq)\).
Determine the moles of \(\text{CuCl}_2\) using its concentration and volume: \(\text{moles of } \text{CuCl}_2 = 0.102 \text{ M} \times 0.0954 \text{ L}\).
Use the stoichiometry of the reaction to find the moles of \(\text{Na}_3\text{PO}_4\) needed. According to the balanced equation, 2 moles of \(\text{Na}_3\text{PO}_4\) react with 3 moles of \(\text{CuCl}_2\).
Calculate the moles of \(\text{Na}_3\text{PO}_4\) required using the ratio from the balanced equation: \(\text{moles of } \text{Na}_3\text{PO}_4 = \frac{2}{3} \times \text{moles of } \text{CuCl}_2\).
Determine the volume of \(0.175 \text{ M } \text{Na}_3\text{PO}_4\) solution needed using its concentration: \(\text{Volume} = \frac{\text{moles of } \text{Na}_3\text{PO}_4}{0.175 \text{ M}}\).

Key Concepts

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

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the proportions of substances involved in a reaction, which is essential for solving problems related to the amounts of reactants needed or products formed.
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Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (M) and is crucial for converting between volume and amount of substance in chemical reactions, enabling us to calculate how much of a solution is required to react with a given amount of another substance.
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Precipitation Reactions

Precipitation reactions occur when two aqueous solutions react to form an insoluble solid, known as a precipitate. Understanding these reactions is important for predicting the formation of solids in solution and for calculating the amounts of reactants needed to achieve complete precipitation, as seen in the given reaction.
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Selective Precipitation