Step-by-Step Guidance for Germanna CHM101 Exam 3 Study Questions

Q1. Write balanced chemical equations for each of the following reactions. Identify the type of chemical reaction in each case.

Background

Topic: Chemical Reactions & Balancing Equations

This question tests your ability to write balanced chemical equations, recognize reaction types (such as double replacement or decomposition), and understand reactant/product relationships.

Key Terms and Formulas:

• Balanced Equation: An equation where the number of atoms for each element is the same on both sides.

• Reaction Types: Double replacement, decomposition, etc.

Step-by-Step Guidance

1. Identify the reactants and products from the written description.

2. Write the chemical formulas for each compound, paying attention to charges and states (aq, s, g).

3. Balance the equation by adjusting coefficients so that the number of atoms for each element is equal on both sides.

4. Determine the reaction type (e.g., double replacement, decomposition) based on the reactants and products.

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Q2. Convert from moles of one chemical to moles of another chemical: 0.436 moles of aluminum chloride to moles of sodium chloride.

Background

Topic: Stoichiometry

This question tests your ability to use a balanced chemical equation to convert between moles of different substances.

Key Terms and Formulas:

• Stoichiometry: The calculation of reactants and products in chemical reactions.

• Mole Ratio: Use coefficients from the balanced equation to relate moles of one substance to another.

Step-by-Step Guidance

1. Write the balanced equation: $2 \text{AlCl}_3(aq) + 3 \text{Na}_2\text{CO}_3(aq) \rightarrow \text{Al}_2(\text{CO}_3)_3(s) + 6 \text{NaCl}(aq)$

2. Identify the mole ratio between AlCl3 and NaCl from the equation (2:6).

3. Set up the conversion: $0.436 \text{ mol AlCl}_3 \times \frac{6 \text{ mol NaCl}}{2 \text{ mol AlCl}_3}$

4. Multiply to find the moles of NaCl produced.

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Q3. Which one of the following is a Brønsted-Lowry acid?

Background

Topic: Acids and Bases

This question tests your understanding of the Brønsted-Lowry definition of acids (proton donors).

Key Terms:

• Brønsted-Lowry Acid: A substance that donates a proton (H+).

Step-by-Step Guidance

1. Review the Brønsted-Lowry definition: acids donate H+ ions.

2. Examine each option to see if it can donate a proton.

3. Consider the chemical structure and whether it contains a hydrogen that can be released as H+.

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Q4. What is the conjugate acid of NH3?

Background

Topic: Acids and Bases

This question tests your understanding of conjugate acid-base pairs.

Key Terms:

• Conjugate Acid: Formed when a base gains a proton (H+).

Step-by-Step Guidance

1. Recall that NH3 is a base; its conjugate acid is formed by adding H+.

2. Write the formula for NH3 after it gains a proton.

3. Check the options for the correct formula.

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Q5. A titration is done to find the molarity of a sulfuric acid solution. The starting volume of acid is 20.0 mL and it takes 25.8 mL of a 2.5 M potassium hydroxide solution to reach the end point. What is the acid’s molarity?

Background

Topic: Acid-Base Titration

This question tests your ability to use titration data to calculate molarity using stoichiometry.

Key Formula:

$n_a M_a V_a = n_b M_b V_b$

• $n_a$ = number of H+ in acid

• $M_a$ = molarity of acid

• $V_a$ = volume of acid

• $n_b$ = number of OH- in base

• $M_b$ = molarity of base

• $V_b$ = volume of base

Step-by-Step Guidance

1. Write the balanced equation for the reaction: $\text{H}_2\text{SO}_4 + 2 \text{KOH} \rightarrow 2 \text{H}_2\text{O} + \text{K}_2\text{SO}_4$

2. Identify $n_a = 2$ (for H+ in H2SO4), $n_b = 1$ (for OH- in KOH).

3. Plug the values into the formula: $M_a = \frac{n_b M_b V_b}{n_a V_a}$

4. Substitute the given values: $M_a = \frac{1 \times 2.5 \text{ M} \times 25.8 \text{ mL}}{2 \times 20.0 \text{ mL}}$

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Q6. A Styrofoam cup calorimeter contains 58.5 mL of water at 22.3°C. An 18.5 g block of copper metal is heated to 99.5°C and then placed in the water. The contents come to equilibrium at 26.1°C. What is the specific heat of the copper in J/g°C?

Background

Topic: Calorimetry

This question tests your ability to use calorimetry data to calculate the specific heat of a substance.

Key Formulas:

• $q_{\text{water}} = m_{\text{water}} C_{\text{water}} \Delta T_{\text{water}}$

• $q_{\text{metal}} = m_{\text{metal}} C_{\text{metal}} \Delta T_{\text{metal}}$

• $q_{\text{water}} = -q_{\text{metal}}$ (energy lost by metal = energy gained by water)

Step-by-Step Guidance

1. Calculate $\Delta T_{\text{water}} = 26.1 - 22.3 = 3.8^\circ \text{C}$

2. Calculate $\Delta T_{\text{copper}} = 26.1 - 99.5 = -73.4^\circ \text{C}$

3. Calculate $q_{\text{water}}$ using $m_{\text{water}} = 58.5 \text{ g}$, $C_{\text{water}} = 4.18 \text{ J/g}^\circ \text{C}$, $\Delta T_{\text{water}} = 3.8^\circ \text{C}$

4. Set $q_{\text{water}} = -q_{\text{metal}}$ and solve for $C_{\text{metal}}$ using $m_{\text{metal}} = 18.5 \text{ g}$, $\Delta T_{\text{metal}} = -73.4^\circ \text{C}$

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