Problem 139 - Chemistry Matter and Change

Question

Write the correct chemical formula for each compound. (Chapter 7\()\) a. a. calcium carbonate b. potassium chlorate c. silver acetate d. copper (II) sulfate e. ammonium phosphate

Step-by-Step Solution

Answer

a. \( \text{CaCO}_3 \), b. \( \text{KClO}_3 \), c. \( \text{AgC}_2\text{H}_3\text{O}_2 \), d. \( \text{CuSO}_4 \), e. \( (\text{NH}_4)_3\text{PO}_4 \).

Step 1: Identify the Ions in the Compounds

First, identify the ions that make up each compound. - For calcium carbonate: Calcium is represented as \( \text{Ca}^{2+} \) and carbonate is represented as \( \text{CO}_3^{2-} \).- For potassium chlorate: Potassium is \( \text{K}^+ \) and chlorate is \( \text{ClO}_3^{-} \).- For silver acetate: Silver is \( \text{Ag}^+ \) and acetate is \( \text{C}_2\text{H}_3\text{O}_2^{-} \), commonly abbreviated as \( \text{CH}_3\text{COO}^{-} \).- For copper (II) sulfate: Copper (II) is \( \text{Cu}^{2+} \) and sulfate is \( \text{SO}_4^{2-} \).- For ammonium phosphate: Ammonium is \( \text{NH}_4^+ \) and phosphate is \( \text{PO}_4^{3-} \).

Step 2: Determine the Chemical Formula by Balancing Charges

Balance the charges of the ions to obtain a neutral compound for each of the given compounds:- Calcium carbonate: Combine as \( \text{CaCO}_3 \) because the charges \( 2^+ \) and \( 2^- \) balance out.- Potassium chlorate: Combine as \( \text{KClO}_3 \) since \( \text{K}^+ \) and \( \text{ClO}_3^- \) are both 1.- Silver acetate: Form \( \text{AgC}_2\text{H}_3\text{O}_2 \) because \( \text{Ag}^+ \) and \( \text{C}_2\text{H}_3\text{O}_2^- \) each have 1 charge.- Copper (II) sulfate: Use \( \text{CuSO}_4 \) as \( 2^+ \) and \( 2^- \) charges balance.- Ammonium phosphate: Combine 3 ammonium ions with 1 phosphate ion to balance the total positive \( 3 \times (+1) = +3 \) with \( (-3) \), resulting in \( (\text{NH}_4)_3\text{PO}_4 \).

Key Concepts

Ion Identification

Identifying ions is a crucial first step in determining the chemical formula of a compound. The ions can either be cations (positive ions) or anions (negative ions). For every compound, you must know which ions are present to figure out how they combine. This involves recognizing the elemental symbol and its associated charge.

• Cations: Metals like calcium, potassium, and copper often form cations, such as \( \text{Ca}^{2+} \), \( \text{K}^+ \), and \( \text{Cu}^{2+} \).
• Anions: These are negatively charged ions like carbonate \( \text{CO}_3^{2-} \) and sulfate \( \text{SO}_4^{2-} \).

In exercise problems, you’ll often be given names that involve these ions. For instance, 'calcium carbonate' involves a calcium ion and a carbonate ion. Correctly identifying these ions will pave the way to correctly balancing them in a chemical formula.

Charge Balancing

Charge balancing is about ensuring that the total positive charge equals the total negative charge in a chemical compound, leading to an overall neutral molecule. Remember, in a stable compound, the positive and negative charges must cancel out.

• For calcium carbonate \( \text{CaCO}_3 \), \( \text{Ca}^{2+} \) pairs with \( \text{CO}_3^{2-} \), cancelling out the charges.
• For ammonium phosphate \( (\text{NH}_4)_3\text{PO}_4 \), three ammonium ions \( 3 \times \text{NH}_4^+ \) provide a total charge of \(+3\), which balances the phosphate’s \(-3\) charge.

To succeed in charge balancing, always determine the least common multiple of charges to know how many of each ion needed for the compound.

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between cations and anions. They typically contain a metal and a non-metal or a non-metal component acting as a polyatomic ion. These compounds have distinct formulas reflecting the minimal ratio of ions needed to achieve charge balance.

• Example: Silver acetate \( \text{AgC}_2\text{H}_3\text{O}_2 \) involves \( \text{Ag}^+ \) and \( \text{C}_2\text{H}_3\text{O}_2^- \) ions.
• The compound forms when these positively and negatively charged ions attract and stick together in a fixed proportion, dictated by their charges.

Understanding that ionic compounds are held together by these strong ionic bonds explains why they have high melting points and conduct electricity well when dissolved in water.

Polyatomic Ions

Polyatomic ions are clusters of atoms bonded together that carry a charge, acting as a single ion in chemical reactions. They can be either positively or negatively charged.Examples from the exercise include:

• Chlorate: \( \text{ClO}_3^- \)
• Acetate: \( \text{C}_2\text{H}_3\text{O}_2^- \) or \( \text{CH}_3\text{COO}^- \)
• Phosphate: \( \text{PO}_4^{3-} \)

Polyatomic ions simplify the writing of chemical formulas as they allow the expression of complicated structures in neat, singular ion forms. When balancing charges in a compound containing these ions, treat the entire polyatomic ion as one unit. Notice that some polyatomic ions like sulfate \( \text{SO}_4^{2-} \) appear in several chemical formulas, emphasizing the importance of remembering their specific structure and charge.