General Chemistry II Sample Test Bank – Step-by-Step Study Guidance

Q1. According to the Bronsted–Lowry definition, which chemical species can function both as an acid and as a base?

Background

Topic: Acid-Base Theory (Bronsted–Lowry)

This question tests your understanding of the Bronsted–Lowry definitions of acids and bases, and the concept of amphiprotic (amphoteric) species.

Key Terms and Concepts:

• Bronsted–Lowry Acid: A substance that can donate a proton (H+).

• Bronsted–Lowry Base: A substance that can accept a proton (H+).

• Amphiprotic (Amphoteric): A species that can act as both an acid and a base.

Step-by-Step Guidance

1. Review the Bronsted–Lowry definitions and identify what it means for a species to act as an acid or a base.

2. For each option, consider if the species can both donate and accept a proton in different reactions.

3. Recall common amphiprotic species, such as HCO3–, H2O, and HSO4–.

4. Eliminate options that can only donate or only accept protons.

Try solving on your own before revealing the answer!

Final Answer: d. HCO3–

HCO3– can act as an acid (donating a proton to become CO32–) or as a base (accepting a proton to become H2CO3).

Q2. In the reaction CN– + H2O → HCN + OH–, which is an acid–base conjugate pair?

Background

Topic: Conjugate Acid–Base Pairs

This question tests your ability to identify conjugate acid–base pairs in a chemical reaction.

Key Terms and Concepts:

• Conjugate Acid–Base Pair: Two species that differ by one proton (H+).

• In a reaction, the acid donates a proton to become its conjugate base; the base accepts a proton to become its conjugate acid.

Step-by-Step Guidance

1. Write the reaction and label each species as acid or base according to the Bronsted–Lowry definition.

2. Identify which species loses a proton and which gains a proton.

3. Find the pair of reactant and product that differ by a single proton.

4. Check each answer choice to see which pair fits this definition.

Try solving on your own before revealing the answer!

Final Answer: b. H2O and OH–

H2O (acid) donates a proton to become OH– (conjugate base); they differ by one H+.

Q4. The pH of a 0.03 M HCl solution is:

Background

Topic: pH Calculations for Strong Acids

This question tests your ability to calculate the pH of a strong acid solution, assuming complete dissociation.

Key Terms and Formulas:

• pH: A measure of the hydrogen ion concentration in solution.

• Formula:

$\text{pH} = -\log_{10}[H^+]$

Step-by-Step Guidance

1. Recognize that HCl is a strong acid and dissociates completely in water.

2. Therefore, $[H^+] = 0.03$ M.

3. Plug the concentration into the pH formula: $\text{pH} = -\log_{10}(0.03)$

4. Calculate the logarithm (you can use a calculator or logarithm rules).

Try solving on your own before revealing the answer!

Final Answer: a. 1.5

Since $\log_{10}(0.03) \approx -1.5$, the pH is 1.5.

Q5. The pH of a 1.0 x 10–3 M Ba(OH)2 solution at 25°C is:

Background

Topic: pH and pOH Calculations for Strong Bases

This question tests your ability to calculate the pH of a strong base solution, considering the number of hydroxide ions produced per formula unit.

Key Terms and Formulas:

• Ba(OH)2: A strong base that dissociates completely, producing 2 OH– per formula unit.

• pOH: $\text{pOH} = -\log_{10}[OH^-]$

• Relationship: $\text{pH} + \text{pOH} = 14$ at 25°C

Step-by-Step Guidance

1. Determine the concentration of OH– ions: $[OH^-] = 2 \times 1.0 \times 10^{-3}$ M

2. Calculate pOH: $\text{pOH} = -\log_{10}([OH^-])$

3. Use the relationship $\text{pH} + \text{pOH} = 14$ to solve for pH.

4. Check your calculations and make sure you account for the stoichiometry of Ba(OH)2.

Try solving on your own before revealing the answer!

Final Answer: d. 11.3

After calculating $[OH^-] = 2.0 \times 10^{-3}$ M, pOH ≈ 2.7, so pH ≈ 11.3.

Q6. Which is the strongest acid?

Background

Topic: Oxyacid Strength Trends

This question tests your understanding of how the number of oxygen atoms in an oxyacid affects its acid strength.

Key Terms and Concepts:

• Oxyacid: An acid in which the acidic proton is bonded to an oxygen atom.

• For acids of the form HClOn, acid strength increases with the number of oxygen atoms.

Step-by-Step Guidance

1. List the acids in order of increasing number of oxygen atoms: HClO, HClO2, HClO3, HClO4.

2. Recall that more oxygen atoms stabilize the negative charge on the conjugate base, making the acid stronger.

3. Identify which acid has the most oxygen atoms.

4. Choose the acid with the highest oxidation state of chlorine.

Try solving on your own before revealing the answer!

Final Answer: d. HClO4

HClO4 (perchloric acid) has the most oxygen atoms and is the strongest acid in this series.