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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 24b

Identify the precipitate (if any) that forms when the following solutions are mixed, and write a balanced equation for each reaction.(b) LiOH and MnCl2

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insert step 1> Identify the ions present in each solution: LiOH dissociates into Li^+ and OH^- ions, while MnCl2 dissociates into Mn^2+ and Cl^- ions.
insert step 2> Determine the possible combinations of cations and anions that could form a precipitate: Li^+ with Cl^- and Mn^2+ with OH^-.
insert step 3> Use solubility rules to determine if any of these combinations form an insoluble compound: LiCl is soluble, but Mn(OH)2 is generally insoluble in water.
insert step 4> Write the balanced chemical equation for the formation of the precipitate: Mn^2+ (aq) + 2 OH^- (aq) -> Mn(OH)2 (s).
insert step 5> Conclude that Mn(OH)2 is the precipitate formed when LiOH and MnCl2 solutions are mixed.

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Key Concepts

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

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble product, known as a precipitate. This process is driven by the formation of a compound that cannot remain dissolved in the solvent, leading to the separation of solid material from the liquid. Understanding solubility rules helps predict whether a precipitate will form when two solutions are mixed.
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Solubility Rules

Solubility rules are guidelines that help predict the solubility of various ionic compounds in water. For example, most hydroxides are insoluble except for those of alkali metals and some alkaline earth metals. Knowing these rules is essential for determining whether a precipitate will form when mixing solutions, as it allows one to identify which products are soluble and which are not.
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Balanced Chemical Equations

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. Balancing is crucial for accurately depicting the conservation of mass during a reaction. In the context of precipitation reactions, writing a balanced equation involves identifying the reactants, the products formed (including any precipitate), and ensuring that the number of atoms for each element is the same on both sides.
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