Q1. What is the electron configuration of a Tc3+ ion?

Background

Topic: Electron Configurations of Ions

This question tests your understanding of how to write electron configurations for transition metal ions, including the order in which electrons are removed when forming cations.

Key Terms and Formulas

• Electron configuration: The arrangement of electrons in an atom or ion, typically written using noble gas notation and subshells (e.g., [Kr]5s24d5).

• Transition metals: For cations, electrons are removed first from the s orbital of the highest principal quantum number (n), then from the d orbitals.

Step-by-Step Guidance

1. Write the ground-state electron configuration for a neutral Tc atom (atomic number 43): .

2. Determine how many electrons must be removed to form Tc3+ (remove 3 electrons).

3. Recall that for transition metals, electrons are removed first from the 5s orbital, then from the 4d orbital.

4. Remove two electrons from the 5s orbital, then one from the 4d orbital. Write the resulting configuration.

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Q2. Write the electron configurations for (a) Ga3+, (b) Cr3+, and (c) Br–.

Background

Topic: Electron Configurations of Ions

This question tests your ability to write electron configurations for main group and transition metal ions, including both cations and anions.

Key Terms and Formulas

• Electron configuration: The arrangement of electrons in an atom or ion, using noble gas notation.

• Cations: Electrons are removed from the highest energy orbitals (highest n value first).

• Anions: Electrons are added to the lowest available energy orbitals.

Step-by-Step Guidance

1. For each ion, write the ground-state electron configuration of the neutral atom (Ga: Z=31, Cr: Z=24, Br: Z=35).

2. For cations (Ga3+, Cr3+), remove the appropriate number of electrons, starting from the highest n value (s before d for transition metals).

3. For anions (Br–), add one electron to the next available orbital.

4. Express each configuration using noble gas notation.

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Q3. Write a balanced chemical equation for the reaction of solid selenium dioxide, SeO2(s), with (a) water, (b) aqueous sodium hydroxide.

Background

Topic: Reactions of Nonmetal Oxides

This question tests your understanding of how nonmetal oxides react with water (to form acids) and with bases (to form salts and water).

Key Terms and Formulas

• Nonmetal oxide: An oxide of a nonmetal element, often acidic in nature.

• Acid formation: Nonmetal oxides react with water to form acids.

• Salt formation: Nonmetal oxides react with bases to form salts and water.

Step-by-Step Guidance

1. For (a), recall the general reaction: .

2. Identify the acid formed when SeO2 reacts with water (compare to CO2 + H2O → H2CO3).

3. For (b), recall the general reaction: .

4. Write the balanced equation for SeO2 reacting with NaOH, forming a salt and water.

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Q4. How many of the following oxides are expected to form acidic solutions in water: SO2, Y2O3, MgO, Cl2O, N2O5?

Background

Topic: Acid-Base Properties of Oxides

This question tests your ability to classify oxides as acidic, basic, or amphoteric based on their position in the periodic table and their chemical nature.

Key Terms and Concepts

• Acidic oxide: Typically a nonmetal oxide that forms an acid when dissolved in water.

• Basic oxide: Typically a metal oxide that forms a base when dissolved in water.

• Amphoteric oxide: An oxide that can react as either an acid or a base.

Step-by-Step Guidance

1. Identify which elements are metals and which are nonmetals in the list of oxides.

2. Recall that nonmetal oxides generally form acidic solutions in water, while metal oxides form basic solutions.

3. Count the number of nonmetal oxides in the list: SO2, Cl2O, N2O5 (nonmetals); Y2O3, MgO (metals).

4. Determine how many of the oxides are expected to form acidic solutions in water.

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Q5. Write a balanced chemical equation for the reaction of solid tetraphosphorus hexoxide with water.

Background

Topic: Reactions of Nonmetal Oxides with Water

This question tests your ability to predict and write balanced equations for the reaction of a nonmetal oxide (P4O6) with water to form an acid.

Key Terms and Concepts

• Tetraphosphorus hexoxide (P4O6): A nonmetal oxide of phosphorus.

• Acid formation: Nonmetal oxides react with water to form acids.

Step-by-Step Guidance

1. Recall the general reaction: .

2. Determine the acid formed when P4O6 reacts with water (compare to P4O10 + H2O → H3PO4).

3. Balance the equation for the reaction of P4O6 with water to form the corresponding acid.

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Q6. Write a balanced equation for the reaction of cesium metal with (a) Cl2(g), (b) H2O(l), (c) H2(g).

Background

Topic: Reactions of Alkali Metals

This question tests your understanding of the typical reactions of alkali metals with halogens, water, and hydrogen gas, including the formation of ionic compounds and redox chemistry.

Key Terms and Concepts

• Alkali metal: Group 1 elements, highly reactive, especially with water and halogens.

• Redox reaction: Involves transfer of electrons; alkali metals are oxidized to +1 ions.

Step-by-Step Guidance

1. For (a), recall the reaction of an alkali metal with a halogen to form an ionic halide (e.g., Cs + Cl2 → CsCl).

2. For (b), recall the reaction of an alkali metal with water to form a hydroxide and hydrogen gas.

3. For (c), recall the reaction of an alkali metal with hydrogen gas to form a metal hydride.

4. Balance each equation, ensuring the correct stoichiometry for all reactants and products.

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Q7. Which of the following statements about the reactivity of an alkali metal M with oxygen gas is or are true?

• (i) Based on their positions in the periodic table, the expected product is the ionic oxide M2O.

• (ii) Some of the alkali metals produce metal peroxides or metal superoxides when they react with oxygen.

• (iii) When dissolved in water, an alkali metal oxide produces a basic solution.

(a) Only one of the statements is true. (b) Statements (i) and (ii) are true. (c) Statements (i) and (iii) are true. (d) Statements (ii) and (iii) are true. (e) All three statements are true.

Background

Topic: Reactivity of Alkali Metals with Oxygen

This question tests your understanding of the products formed when alkali metals react with oxygen and the properties of their oxides.

Key Terms and Concepts

• Alkali metal oxides: Can be simple oxides (M2O), peroxides (M2O2), or superoxides (MO2), depending on the metal.

• Basic solution: Metal oxides react with water to form basic solutions.

Step-by-Step Guidance

1. Review statement (i): Is the expected product always M2O for all alkali metals?

2. Review statement (ii): Do some alkali metals form peroxides or superoxides instead of simple oxides?

3. Review statement (iii): Does dissolving an alkali metal oxide in water always produce a basic solution?

4. Determine which statements are correct based on periodic trends and chemical properties.

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Q8. Write a balanced equation for the expected reaction between potassium metal and elemental sulfur, S(s).

Background

Topic: Reactions of Alkali Metals with Nonmetals

This question tests your ability to predict and write balanced equations for the reaction of an alkali metal with a nonmetal (sulfur).

Key Terms and Concepts

• Alkali metal sulfide: The product of an alkali metal reacting with sulfur, typically M2S.

• Balancing equations: Ensure the correct stoichiometry for all reactants and products.

Step-by-Step Guidance

1. Recall the general reaction: , where M is an alkali metal.

2. Substitute potassium (K) for M in the equation.

3. Balance the equation to ensure the correct stoichiometry.

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