Comprehensive Step-by-Step Guidance for General Chemistry 115 Final Exam Practice

Q1. Give the name or symbol for each of the following: Se²⁻, Na₂SO₃, Hydrogen phosphate, HClO₂, Al₂(CO₃)₃, HBr(aq), Copper(II) perchlorate, Strontium oxide, Calcium nitrite, Potassium azide.

Background

Topic: Chemical Nomenclature (Ions, Ionic Compounds, Acids, Covalent Compounds)

This question tests your ability to name ions and compounds, and to write correct chemical symbols or formulas based on their names.

Key Terms and Concepts:

• Monatomic ions: Ions formed from single atoms (e.g., Se²⁻ is the selenide ion).

• Polyatomic ions: Ions composed of more than one atom (e.g., SO₃²⁻ is sulfite).

• Acids: Compounds that produce H⁺ in water; naming depends on the anion (e.g., HBr(aq) is hydrobromic acid).

• Stock system: Used for transition metals to indicate charge (e.g., Copper(II) = Cu²⁺).

• Binary and ternary compounds: Binary = two elements; ternary = three or more.

Step-by-Step Guidance

1. For each formula or name, identify whether it is an ion, an acid, or a compound. For example, Se²⁻ is an ion, Na₂SO₃ is an ionic compound, HClO₂ is an acid, etc.

2. Recall the rules for naming ions and compounds:

   • Monatomic anions: root of element + "-ide" (e.g., Se²⁻ is selenide).

   • Polyatomic ions: memorize common names (e.g., SO₃²⁻ is sulfite).

   • Acids: If the anion ends in "-ite," the acid name ends in "-ous acid" (e.g., HClO₂ is chlorous acid).

   • For compounds with metals that have variable charges, use Roman numerals (e.g., Copper(II) perchlorate).

3. For each, write the corresponding name or formula, applying the above rules. For example, for Na₂SO₃, identify the cation (Na⁺) and the anion (SO₃²⁻), then name as sodium sulfite.

4. For acids, remember to add "hydro-" for binary acids (e.g., HBr(aq) is hydrobromic acid), and use the appropriate suffix for oxyacids (e.g., HClO₂ is chlorous acid).

Try solving on your own before revealing the answer!

Final Answers:

• Se²⁻: selenide ion

• Na₂SO₃: sodium sulfite

• Hydrogen phosphate: HPO₄²⁻

• HClO₂: chlorous acid

• Al₂(CO₃)₃: aluminum carbonate

• HBr(aq): hydrobromic acid

• Copper(II) perchlorate: Cu(ClO₄)₂

• Strontium oxide: SrO

• Calcium nitrite: Ca(NO₂)₂

• Potassium azide: KN₃

Each answer follows the standard rules for naming ions, acids, and compounds as outlined above.

Q2. Write the formula for each compound: a) Tetraphosphorus decaoxide b) Potassium sulfate c) Barium chlorate d) Sulfur dioxide e) Magnesium chloride

Background

Topic: Writing Chemical Formulas from Names (Covalent and Ionic Compounds)

This question tests your ability to translate compound names into correct chemical formulas, using prefixes for covalent compounds and charges for ionic compounds.

Key Terms and Concepts:

• Prefixes: Used for covalent compounds (e.g., tetra- = 4, deca- = 10).

• Ionic compounds: Combine cations and anions in ratios that balance charges.

• Common polyatomic ions: sulfate = SO₄²⁻, chlorate = ClO₃⁻, nitrite = NO₂⁻, etc.

Step-by-Step Guidance

1. For covalent compounds (those with prefixes), use the prefix to determine the number of each atom. For example, "tetraphosphorus decaoxide" means 4 phosphorus and 10 oxygen atoms.

2. For ionic compounds, identify the cation and anion, write their symbols, and balance the charges to determine the correct formula.

3. For each compound, write the formula by combining the elements or ions in the correct ratio.

Try solving on your own before revealing the answer!

Final Answers:

• a) Tetraphosphorus decaoxide: P₄O₁₀

• b) Potassium sulfate: K₂SO₄

• c) Barium chlorate: Ba(ClO₃)₂

• d) Sulfur dioxide: SO₂

• e) Magnesium chloride: MgCl₂

Prefixes and charge balancing are used to determine the correct formulas.