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Ch.4 - Reactions in Aqueous Solution
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.4 - Reactions in Aqueous SolutionProblem 18a
Chapter 4, Problem 18a

Specify what ions are present upon dissolving each of the following substances in water: (a) MgI2

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Step 1: Understand that when ionic compounds dissolve in water, they dissociate into their constituent ions. This is because water molecules are polar and can surround and isolate the ions.
Step 2: Identify the ions that make up the ionic compound. In this case, MgI2 is made up of Mg2+ and I- ions.
Step 3: Determine the ratio of the ions in the compound. For MgI2, there is one Mg2+ ion for every two I- ions.
Step 4: Therefore, when MgI2 dissolves in water, it dissociates into Mg2+ and I- ions. The ratio of ions will be the same as in the solid compound, so for every one unit of MgI2 that dissolves, one Mg2+ ion and two I- ions will be produced.

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Key Concepts

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

Dissociation of Ionic Compounds

Ionic compounds, when dissolved in water, undergo dissociation, breaking apart into their constituent ions. This process occurs because the polar water molecules surround and stabilize the individual ions, allowing them to separate from the solid lattice structure. Understanding this concept is crucial for predicting the ions formed when a specific ionic compound is dissolved.
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Ionic Charges

Each ion has a specific charge based on the number of electrons gained or lost relative to the neutral atom. For example, magnesium (Mg) typically loses two electrons to form a Mg²⁺ ion, while iodide (I) gains one electron to form I⁻ ions. Recognizing the charges of the ions is essential for determining the overall composition of the solution after dissolution.
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Stoichiometry of Dissolution

The stoichiometry of dissolution refers to the ratio of ions produced when an ionic compound dissolves in water. For instance, when magnesium iodide (MgI₂) dissolves, it produces one Mg²⁺ ion and two I⁻ ions. Understanding this ratio is important for calculating the concentration of each ion in solution and for predicting the behavior of the solution in chemical reactions.
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