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Ch.5 - Introduction to Solutions and Aqueous Solutions
Chapter 5, Problem 34

Consider the reaction: Li2S(aq) + Co(NO3)2(aq) → 2 LiNO3(aq) + CoS(s) What volume of 0.150 M Li2S solution is required to completely react with 125 mL of 0.150 M Co(NO3)2?

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1
Identify the balanced chemical equation: Li_2S(aq) + Co(NO_3)_2(aq) \rightarrow 2 LiNO_3(aq) + CoS(s).
Determine the stoichiometry of the reaction: 1 mole of Li_2S reacts with 1 mole of Co(NO_3)_2.
Calculate the moles of Co(NO_3)_2 using its concentration and volume: \text{moles of Co(NO}_3\text{)}_2 = 0.150 \text{ M} \times 0.125 \text{ L}.
Use the stoichiometry of the reaction to find the moles of Li_2S needed: \text{moles of Li}_2\text{S} = \text{moles of Co(NO}_3\text{)}_2.
Calculate the volume of 0.150 M Li_2S solution required using its concentration: \text{Volume of Li}_2\text{S} = \frac{\text{moles of Li}_2\text{S}}{0.150 \text{ M}}.

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Key Concepts

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

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows us to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. In this case, understanding the stoichiometric coefficients from the balanced equation is essential to determine the volume of Li<sub>2</sub>S needed to react with Co(NO<sub>3</sub>)<sub>2</sub>.
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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). In this problem, both Li<sub>2</sub>S and Co(NO<sub>3</sub>)<sub>2</sub> solutions are given in molarity, which is crucial for calculating the number of moles present in the given volumes and for determining how much Li<sub>2</sub>S is needed to react completely with the cobalt nitrate.
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Limiting Reactant

The limiting reactant is the substance that is completely consumed first in a chemical reaction, thus determining the maximum amount of product that can be formed. Identifying the limiting reactant is key to solving stoichiometric problems, as it dictates how much of the other reactants are required. In this scenario, knowing which reactant limits the reaction will help in calculating the necessary volume of Li<sub>2</sub>S solution.
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