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Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 61c

Predict the chemical formula for the ionic compound formed by (c) Al3+ and CH3COO-

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1
Identify the charges of the ions involved: Al3+ has a charge of +3, and CH3COO- (acetate ion) has a charge of -1.
Determine the lowest common multiple of the charges to balance the overall charge to zero. In this case, the lowest common multiple of 3 and 1 is 3.
Use the common multiple to determine the number of each ion needed to balance the charges. You need three acetate ions to balance one Al3+ ion.
Write the chemical formula by placing the cation first followed by the anion. Since you need three acetate ions for each aluminum ion, the formula will include three CH3COO- for each Al3+.
Combine the ions in the correct ratio to write the final formula: Al(CH3COO)3.

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Key Concepts

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

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons, resulting in the formation of positively charged cations and negatively charged anions. The electrostatic attraction between these oppositely charged ions leads to the creation of a stable compound. Understanding the charges of the ions involved is crucial for predicting the correct formula of the resulting ionic compound.
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Charge Balance

In ionic compounds, the total positive charge must balance the total negative charge to achieve electrical neutrality. This means that the ratio of cations to anions must be adjusted according to their respective charges. For example, if a cation has a charge of +3 and an anion has a charge of -1, three anions are needed to balance one cation, resulting in a formula that reflects this ratio.
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Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms that are covalently bonded and carry a net charge. In this case, the acetate ion (CH3COO-) is a common polyatomic ion with a charge of -1. Recognizing polyatomic ions and their charges is essential for correctly writing the formula of ionic compounds that include them.
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