Problem 139 - Chemistry Matter and Change

Question

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

Step-by-Step Solution

Answer

The correct chemical formulas for each compound are: a. \(CaCO_{3}\) b. \(KClO_{3}\) c. \(AgCH_{3}COO\) d. \(CuSO_{4}\) e. \((NH_{4})_{3}PO_{4}\)

Step 1: (a) Identify elements and charges in calcium carbonate

Calcium carbonate consists of calcium (Ca) which has a charge of +2, carbon (C), and three oxygen atoms (O). Carbon and oxygen form a carbonate ion (CO3) with a charge of -2.

Step 2: (a) Balance charges and write the formula for calcium carbonate

Since the charges of calcium and carbonate ions are equal and opposite (+2 and -2), we can combine one calcium ion and one carbonate ion to form the formula for calcium carbonate: \(CaCO_{3}\).

Step 3: (b) Identify elements and charges in potassium chlorate

Potassium chlorate contains potassium (K) which has a charge of +1, chlorine (Cl), and three oxygen atoms (O). Chlorine and oxygen form a chlorate ion (ClO3) with a charge of -1.

Step 4: (b) Balance charges and write the formula for potassium chlorate

Since the charges of potassium and chlorate ions are equal and opposite (+1 and -1), we can combine one potassium ion and one chlorate ion to form the formula for potassium chlorate: \(KClO_{3}\).

Step 5: (c) Identify elements and charges in silver acetate

Silver acetate consists of silver (Ag) which has a charge of +1, two carbon atoms (C), and four oxygen atoms (O). Two carbon and four oxygen atoms form an acetate ion (CH3COO) with a charge of -1.

Step 6: (c) Balance charges and write the formula for silver acetate

Since the charges of silver and acetate ions are equal and opposite (+1 and -1), we can combine one silver ion and one acetate ion to form the formula for silver acetate: \(AgCH_{3}COO\).

Step 7: (d) Identify elements and charges in copper (II) sulfate

Copper (II) sulfate contains copper (Cu) which has a charge of +2, sulfur (S), and four oxygen atoms (O). Sulfur and four oxygen atoms form a sulfate ion (SO4) with a charge of -2.

Step 8: (d) Balance charges and write the formula for copper (II) sulfate

Since the charges of copper and sulfate ions are equal and opposite (+2 and -2), we can combine one copper ion and one sulfate ion to form the formula for copper (II) sulfate: \(CuSO_{4}\).

Step 9: (e) Identify elements and charges in ammonium phosphate

Ammonium phosphate consists of ammonium ion (NH4) which has a charge of +1, and phosphate ion (PO4) that has a charge of -3.

Step 10: (e) Balance charges and write the formula for ammonium phosphate

To balance the charges in ammonium phosphate, we need to have three ammonium ions for each phosphate ion. So, the formula for ammonium phosphate is: \((NH_{4})_{3}PO_{4}\).

Key Concepts

Ionic Compounds

Ionic compounds are formed when positive and negative ions attract each other to create a stable entity. These compounds are typically made up of metal and non-metal elements.

• Forming Ionic Bonds: The metal element loses electrons to become a positively charged ion (cation), while the non-metal gains electrons to become a negatively charged ion (anion). The opposite charges attract, forming a strong ionic bond.
• Characteristics: Ionic compounds tend to have high melting and boiling points and are usually solid at room temperature. They can conduct electricity when dissolved in water due to the presence of charged ions.

The example of calcium carbonate (\(CaCO_{3}\)) from the exercise highlights how calcium ions (\(+2\)) bond with carbonate ions (\(-2\)) to create a stable compound.

Polyatomic Ions

Polyatomic ions are ions made up of more than one atom. They act as a single charged entity, often maintaining neutrality or stability by gaining or losing extra electrons.

• Examples: Common polyatomic ions include sulfate (\(SO_4^{2-}\)), acetate (\(CH_3COO^-\)), nitrate (\(NO_3^-\)), and carbonate (\(CO_3^{2-}\)).
• Role in Compounds: These ions combine with other ions to form neutral compounds. For instance, acetate combines with silver in silver acetate (\(AgCH_3COO\)).

In the exercise above, the compound ammonium phosphate involves both a polyatomic cation (\((NH_{4})^+\)) and a polyatomic anion (\(PO_4^{3-}\)). This showcases how polyatomic ions can come together to form a more complex ionic compound.

Balancing Charges

Balancing charges is an essential step in writing the chemical formula for ionic compounds. For a compound to be neutral, the total positive charge must equal the total negative charge.

Steps to Balance Charges:

• Identify the Charges: Determine the charge of each ion involved in the compound. For example, potassium (\(+1\)) and chlorate (\(-1\)) ions in potassium chlorate.
• Calculate the Ratios: Use the charges to determine the ratio of ions needed to balance out the charges. In potassium chlorate (\(KClO_3\)), one potassium ion balances with one chlorate ion.
• Form the Chemical Formula: Use the balanced ratios to write the simplest form of the formula. Ensure that it represents the correct number of each type of ion.

This step is crucial in forming compounds like ammonium phosphate, where multiple ammonium ions are required to balance a single phosphate ion.

Chemical Nomenclature

Chemical nomenclature is the system of naming compounds and writing their formulas. Understanding how to name different chemical compounds is vital for clear communication in science.

• Simplifying Formula Writing: For ionic compounds, the metal ions are named first, followed by the name of the non-metal, with the suffix "-ide," or the name of the polyatomic ion. For example, copper (II) sulfate consists of a copper ion with a +2 charge and a sulfate ion with a -2 charge.
• Ionic Charges and Roman Numerals: When a metal can form more than one positive charge, Roman numerals indicate the charge, such as copper (II) sulfate (\(CuSO_4\)).
• Handling Polyatomic ions: The names of familiar polyatomic ions are used directly in the compound's name, like ammonium in ammonium phosphate (\((NH_4)_3PO_4\)).

Correct nomenclature and formula writing help avoid ambiguity and ensure proper chemical interpretation in research, industry, and education.