CHE 1101 Final Exam Review – Step-by-Step Guidance for Practice Problems

Q1. Identify each property or change as chemical or physical:

Background

Topic: Chemical and Physical Properties/Changes

This question tests your understanding of the difference between chemical and physical properties and changes. Chemical changes involve the formation of new substances, while physical changes do not.

Key Terms:

• Chemical property: Describes a substance's ability to undergo a specific chemical change.

• Physical property: Can be observed or measured without changing the substance's identity.

• Chemical change: Results in the formation of new substances.

• Physical change: Does not change the substance's identity.

Step-by-Step Guidance

1. For each example, ask yourself: Does the process change the chemical identity of the substance?

2. If the process creates a new substance or involves a chemical reaction (like burning or rusting), it's a chemical change/property.

3. If the process only changes the physical state or appearance (like boiling or grinding), it's a physical change/property.

4. Review each item and classify accordingly, but stop before listing the final answers.

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Q2. Convert the following:

Background

Topic: Unit Conversions

This question tests your ability to convert between different units using conversion factors.

Key Terms and Formulas:

• Conversion factor: A ratio used to convert from one unit to another.

• Common conversions:

  • 1 mg = 0.001 g

  • 1 mm = 0.1 cm

  • 1 L = 1000 mL

  • 1 inch = 2.54 cm; 1 mile = 5280 ft; 1 ft = 12 in

Step-by-Step Guidance

1. Write down the starting value and unit for each part.

2. Set up the conversion factor so that the starting unit cancels and the desired unit remains.

3. Multiply by the conversion factor(s) as needed.

4. Stop before calculating the final value.

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Q3. How many significant figures are the following values?

Background

Topic: Significant Figures

This question tests your ability to count significant digits in a number, which is important for reporting measurements accurately.

Key Terms:

• Significant figures: Digits in a number that are meaningful in terms of precision.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros are significant if there is a decimal point.

Step-by-Step Guidance

1. For each value, identify all nonzero digits.

2. Apply the rules for zeros (leading, trailing, captive).

3. Count the number of significant digits for each value, but stop before stating the final count.

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Q4. Convert the following to proper scientific notation:

Background

Topic: Scientific Notation

This question tests your ability to express numbers in scientific notation, which is useful for very large or small values.

Key Terms:

• Scientific notation: A way to write numbers as $a \times 10^n$ where $1 \leq a < 10$ and $n$ is an integer.

Step-by-Step Guidance

1. For each number, move the decimal point so that only one nonzero digit is to the left.

2. Count how many places you moved the decimal; this is the exponent $n$.

3. Write the number in the form $a \times 10^n$, but stop before writing the final notation.

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Q5. Complete the following chart, assume atoms are neutral if not otherwise indicated:

Background

Topic: Atomic Structure

This question tests your understanding of atomic number, mass number, and how to determine the number of protons, neutrons, and electrons in an atom or ion.

Key Terms and Formulas:

• Atomic number ($Z$): Number of protons.

• Mass number ($A$): Number of protons + neutrons.

• Number of neutrons: $A - Z$

• Number of electrons: For neutral atoms, equals $Z$; for ions, adjust for charge.

Step-by-Step Guidance

1. For each element, identify the atomic number ($Z$) and mass number ($A$).

2. Calculate the number of neutrons using $A - Z$.

3. Determine the number of electrons, considering the charge if it's an ion.

4. Fill in the chart, but stop before completing all entries.

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Q6. Name the following compounds:

Background

Topic: Chemical Nomenclature

This question tests your ability to name ionic and covalent compounds according to IUPAC rules.

Key Terms:

• Ionic compound: Metal + nonmetal; use Roman numerals for transition metals.

• Covalent compound: Nonmetal + nonmetal; use prefixes (mono-, di-, tri-, etc.).

• Acids: Special naming rules for compounds with H.

Step-by-Step Guidance

1. Identify if the compound is ionic, covalent, or an acid.

2. Apply the appropriate naming rules for each type.

3. Write the name for each compound, but stop before listing all names.

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Q7. Find the percent composition of the following:

Background

Topic: Percent Composition

This question tests your ability to calculate the percent by mass of each element in a compound.

Key Formula:

$\text{Percent composition} = \frac{\text{mass of element in 1 mol}}{\text{molar mass of compound}} \times 100\%$

Step-by-Step Guidance

1. Write the formula for each compound and determine the molar mass.

2. Calculate the mass of each element in one mole of the compound.

3. Use the formula above to find the percent composition for each element, but stop before calculating the final percentages.

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Q8. Use the percent compositions from the previous question to answer the following:

Background

Topic: Application of Percent Composition

This question tests your ability to use percent composition to find the mass of a specific element in a given mass of compound.

Key Formula:

$\text{Mass of element} = \text{percent composition} \times \text{total mass of compound} \div 100$

Step-by-Step Guidance

1. Use the percent composition values from Q7.

2. Multiply the percent composition (as a decimal) by the total mass given.

3. Stop before calculating the final mass.

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Q9. How many moles of chlorine are in 2.30 mol CCl4?

Background

Topic: Mole Relationships in Compounds

This question tests your ability to use the formula of a compound to determine the number of moles of a specific element.

Key Formula:

$\text{Moles of element} = \text{moles of compound} \times \text{number of atoms of element per formula unit}$

Step-by-Step Guidance

1. Identify the number of chlorine atoms in one molecule of CCl4.

2. Multiply the number of moles of CCl4 by the number of chlorine atoms per molecule.

3. Stop before calculating the final number of moles.

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Q10. An unknown compound contains 36.86% nitrogen and 63.14% oxygen. What is the empirical formula for this compound?

Background

Topic: Empirical Formula Determination

This question tests your ability to use percent composition to determine the simplest whole-number ratio of atoms in a compound.

Key Steps:

• Assume 100 g of compound.

• Convert mass of each element to moles.

• Divide by the smallest number of moles to get the ratio.

• Stop before writing the empirical formula.

Step-by-Step Guidance

1. Assume 100 g sample: 36.86 g N, 63.14 g O.

2. Convert each mass to moles using molar masses: $\text{N} = 14.01$ g/mol, $\text{O} = 16.00$ g/mol.

3. Divide each by the smallest number of moles to get the ratio.

4. Stop before writing the empirical formula.

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Q11. Lithium oxalate has the following percent composition: 13.62% Li, 23.58% C, and 62.81% O. If the molar mass of lithium oxalate is 101.88 g/mol, what is its molecular formula?

Background

Topic: Molecular Formula Determination

This question tests your ability to use percent composition and molar mass to determine the molecular formula of a compound.

Key Steps:

• Find the empirical formula using percent composition.

• Calculate the empirical formula mass.

• Divide the molar mass by the empirical formula mass to find the multiplier.

• Multiply subscripts in empirical formula by the multiplier to get molecular formula.

• Stop before writing the molecular formula.

Step-by-Step Guidance

1. Assume 100 g sample: 13.62 g Li, 23.58 g C, 62.81 g O.

2. Convert each mass to moles using molar masses: Li = 6.94 g/mol, C = 12.01 g/mol, O = 16.00 g/mol.

3. Find the simplest ratio and write the empirical formula.

4. Calculate empirical formula mass and divide molar mass by this value to find the multiplier.

5. Stop before writing the molecular formula.

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Q12. Use the following reaction to answer the questions below: 3 H2 + N2 → 2 NH3

Background

Topic: Stoichiometry

This question tests your ability to use balanced chemical equations to relate moles, mass, and particles of reactants and products.

Key Terms and Formulas:

• Mole ratio: Use coefficients from balanced equation.

• Molar mass: Needed to convert grams to moles.

• Avogadro's number: $6.022 \times 10^{23}$ particles/mol.

Step-by-Step Guidance

1. For each part, start by converting grams to moles using molar mass if needed.

2. Use the mole ratio from the balanced equation to relate reactants and products.

3. For particles, convert moles to particles using Avogadro's number.

4. Stop before calculating the final values for each part.

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Q13. Balance the following equations and label the type of chemical reaction:

Background

Topic: Chemical Equations and Reaction Types

This question tests your ability to balance chemical equations and identify reaction types (combustion, synthesis, decomposition, single/double replacement).

Key Terms:

• Balancing equations: Make sure the number of atoms of each element is equal on both sides.

• Reaction types: Know the characteristics of each type.

Step-by-Step Guidance

1. Write the unbalanced equation for each reaction.

2. Balance atoms one element at a time, starting with the most complex molecule.

3. Identify the reaction type based on reactants and products.

4. Stop before writing the fully balanced equations and reaction types.

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Q14. What is the molarity of a solution containing 32.5 g of NaCl dissolved in 500. mL of solution?

Background

Topic: Solution Concentration (Molarity)

This question tests your ability to calculate molarity, which is moles of solute per liter of solution.

Key Formula:

$\text{Molarity} (M) = \frac{\text{moles of solute}}{\text{liters of solution}}$

Step-by-Step Guidance

1. Calculate moles of NaCl: $\text{moles} = \frac{\text{mass}}{\text{molar mass}}$

2. Convert 500 mL to liters.

3. Set up the molarity formula and plug in the values.

4. Stop before calculating the final molarity.

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Q15. How much of a stock solution of 3.0 M HCl is needed to make 25 mL of 0.10 M HCl?

Background

Topic: Dilution Calculations

This question tests your ability to use the dilution equation to prepare solutions of desired concentration.

Key Formula:

$M_1 V_1 = M_2 V_2$

Step-by-Step Guidance

1. Identify $M_1$ (stock concentration), $M_2$ (final concentration), $V_2$ (final volume).

2. Rearrange the formula to solve for $V_1$ (volume of stock solution needed).

3. Plug in the values and stop before calculating $V_1$.

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Q16. Draw the Lewis structure, mark the dipoles and identify polarity, identify the molecular geometry and electron domain geometry, and find the formal charge on each atom of the following compounds: a. CF4, b. NH3, c. CF2S, and d. CS2. Identify the hybridization of the central atom.

Background

Topic: Molecular Structure and Bonding

This question tests your ability to draw Lewis structures, determine molecular geometry, polarity, formal charge, and hybridization.

Key Concepts:

• Lewis structure: Shows arrangement of electrons.

• Dipole: Arrow showing direction of electron density.

• Molecular geometry: Shape of molecule (VSEPR theory).

• Formal charge: $\text{FC} = \text{valence electrons} - \text{nonbonding electrons} - \frac{1}{2}\text{bonding electrons}$

• Hybridization: Based on electron domains around central atom.

Step-by-Step Guidance

1. Draw the Lewis structure for each compound.

2. Mark dipoles based on electronegativity values.

3. Identify molecular and electron domain geometry using VSEPR theory.

4. Calculate formal charge for each atom.

5. Determine hybridization of central atom.

6. Stop before completing all details for each compound.

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Q17. Write the full electron configuration and noble gas notation for the following: a. C, b. K+, and c. Fe3+.

Background

Topic: Electron Configuration

This question tests your ability to write electron configurations for atoms and ions, including noble gas shorthand.

Key Concepts:

• Electron configuration: Order in which electrons fill orbitals.

• Noble gas notation: Use the previous noble gas to abbreviate.

• Ions: Adjust electron count for charge.

Step-by-Step Guidance

1. Determine the atomic number and electron count for each atom/ion.

2. Write the full electron configuration using the Aufbau principle.

3. Write the noble gas notation.

4. Stop before writing the final configurations.

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Q18. Write and balance the neutralization reaction of sodium hydroxide and nitric acid. Write the complete ionic and net ionic equation of the reaction.

Background

Topic: Acid-Base Reactions and Ionic Equations

This question tests your ability to write balanced equations for neutralization reactions and to identify complete and net ionic equations.

Key Concepts:

• Neutralization: Acid + base → salt + water.

• Complete ionic equation: Shows all ions in solution.

• Net ionic equation: Shows only ions involved in the reaction.

Step-by-Step Guidance

1. Write the balanced molecular equation for NaOH + HNO3.

2. Write the complete ionic equation, separating strong electrolytes into ions.

3. Identify and cancel spectator ions to write the net ionic equation.

4. Stop before writing the final equations.

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Q19. Write the balanced chemical equation and net ionic equation of the reaction of aluminum chloride and silver nitrate. Make sure to consider solubility rules.

Background

Topic: Precipitation Reactions and Solubility

This question tests your ability to write balanced equations and net ionic equations, considering solubility rules.

Key Concepts:

• Solubility rules: Determine which products are soluble/insoluble.

• Net ionic equation: Only shows ions that form a precipitate.

Step-by-Step Guidance

1. Write the balanced molecular equation for AlCl3 + AgNO3.

2. Use solubility rules to identify the precipitate.

3. Write the complete ionic equation.

4. Write the net ionic equation by removing spectator ions.

5. Stop before writing the final equations.

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Q20. Write the balanced chemical equation for the reaction of zinc and copper (II) sulfate. Identify which substance is oxidized and which is reduced in the reaction.

Background

Topic: Redox Reactions

This question tests your ability to write balanced equations for redox reactions and identify oxidation and reduction.

Key Concepts:

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Redox reaction: Transfer of electrons between substances.

Step-by-Step Guidance

1. Write the balanced equation for Zn + CuSO4.

2. Assign oxidation states to each element.

3. Identify which element is oxidized (increase in oxidation state) and which is reduced (decrease in oxidation state).

4. Stop before stating which is oxidized/reduced.

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Q21. What would be the change in internal energy for a process in which a system emits 110 J of heat to the surroundings and has 65 J of work done on the system?

Background

Topic: Thermodynamics (First Law)

This question tests your ability to use the first law of thermodynamics to calculate the change in internal energy.

Key Formula:

$\Delta U = q + w$

• $q$ = heat (negative if emitted)

• $w$ = work (positive if done on system)

Step-by-Step Guidance

1. Assign signs to $q$ and $w$ based on the description.

2. Plug values into the formula $\Delta U = q + w$.

3. Stop before calculating the final value.

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Q22. Calculate the enthalpy change for the combustion of 1 mole of methane (CH4). The heat of formations are as follows: CO2 = -393.5 kJ/mol, H2O (g) = -285.8 kJ/mol, and CH4 = -74.6 kJ/mol.

Background

Topic: Enthalpy Calculations (Hess's Law)

This question tests your ability to use standard enthalpies of formation to calculate reaction enthalpy.

Key Formula:

$\Delta H_{rxn} = \sum \Delta H_f^{\circ} (\text{products}) - \sum \Delta H_f^{\circ} (\text{reactants})$

Step-by-Step Guidance

1. Write the balanced equation for combustion of CH4.

2. List the enthalpy of formation values for each reactant and product.

3. Plug values into the formula above.

4. Stop before calculating the final enthalpy change.

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Q23. What is the final temperature of 23.0 mL of water starting at 22.0 °C when 860 J of heat is added? (density of water is 1.00 g/mL, specific heat of water is 4.18 J/g°C)

Background

Topic: Calorimetry

This question tests your ability to use the relationship between heat, mass, specific heat, and temperature change.

Key Formula:

$q = m c \Delta T$

• $q$ = heat added (J)

• $m$ = mass (g)

• $c$ = specific heat (J/g°C)

• $\Delta T$ = change in temperature (°C)

Step-by-Step Guidance

1. Calculate mass of water using volume and density.

2. Set up the equation $q = m c \Delta T$ and solve for $\Delta T$.

3. Add $\Delta T$ to the initial temperature to find the final temperature.

4. Stop before calculating the final temperature.

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