CHE 1101 Final Exam Review – Step-by-Step Chemistry Guidance

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

Background

Topic: Chemical vs. Physical Properties and 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: "Is the substance's identity changing, or is it just a change in form or appearance?"

2. Recall that chemical changes often involve reactions (burning, rusting, baking), while physical changes involve changes in state or form (melting, boiling, grinding).

3. Apply these definitions to each item and decide if it is a chemical or physical property/change.

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Q2. Convert the following:

Background

Topic: Unit Conversions

This question tests your ability to convert between units using dimensional analysis.

Key Terms and Formulas:

• Dimensional Analysis: A method to convert units using conversion factors.

• Conversion Factors: Relationships between units (e.g., 1 g = 1000 mg, 1 cm = 10 mm, 1 L = 1000 mL).

Step-by-Step Guidance

1. Write the starting value and unit for each conversion.

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

3. Multiply the starting value by the conversion factor.

4. Check your answer to ensure the units are correct.

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Q3. How many significant figures are the following values?

Background

Topic: Significant Figures

This question tests your ability to identify the number of significant digits in a measurement.

Key Terms:

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

• Rules: 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 non-zero digits as significant.

2. Apply rules for zeros: leading, captive, and trailing.

3. Count the total number of significant digits for each value.

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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 $1 \leq a < 10$.

Step-by-Step Guidance

1. Identify the decimal point location in the original number.

2. Move the decimal so only one non-zero digit is to its left.

3. Count how many places you moved the decimal to determine the exponent.

4. Write the number in the form $a \times 10^n$.

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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.

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 number of protons; for ions, adjust for charge.

Step-by-Step Guidance

1. Identify the atomic number ($Z$) for each element.

2. Use the mass number ($A$) to find the number of neutrons: $\text{Neutrons} = A - Z$.

3. For neutral atoms, electrons = protons. For ions, adjust electrons based on charge.

4. Fill in the chart for each entry using these relationships.

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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 cation and anion names.

• Covalent Compound: Nonmetal + nonmetal; use prefixes for number of atoms.

• Acids: Special naming rules for compounds with hydrogen.

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 based on its formula.

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Q7. Find the percent composition of the following:

Background

Topic: Percent Composition

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

Key Formula:

$\text{Percent Composition} = \frac{\text{Mass of element in 1 mole}}{\text{Molar mass of compound}} \times 100\%$

Step-by-Step Guidance

1. Write the formula for the 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.

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

Background

Topic: Mass Calculations Using Percent Composition

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

Key Formula:

$\text{Mass of element} = \text{Percent composition} \times \text{Total mass of sample}$

Step-by-Step Guidance

1. Identify the percent composition of the element from the previous question.

2. Multiply the percent (as a decimal) by the total mass of the sample.

3. Set up the calculation for each part.

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

3. Set up the calculation to find the moles of chlorine.

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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 using molar mass.

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

• Adjust to whole numbers if necessary.

Step-by-Step Guidance

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

2. Calculate moles of N: $\frac{36.86}{14.01}$

3. Calculate moles of O: $\frac{63.14}{16.00}$

4. Divide both mole values by the smallest to get the ratio.

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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 find the molecular formula.

Key Steps:

• Find empirical formula using percent composition.

• Calculate empirical formula mass.

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

• Multiply subscripts in empirical formula by multiplier to get 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 to moles: $\frac{13.62}{6.94}$ for Li, $\frac{23.58}{12.01}$ for C, $\frac{62.81}{16.00}$ for O.

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

4. Find empirical formula mass and compare to molar mass to find multiplier.

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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 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.

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. Set up the calculation for each part, stopping before the final computation.

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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.

Key Terms:

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

• Reaction Types: Combustion, synthesis, decomposition, single replacement, double replacement.

Step-by-Step Guidance

1. Write the unbalanced equation.

2. Count atoms of each element on both sides.

3. Add coefficients to balance atoms.

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

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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: $\frac{32.5}{58.44}$ (molar mass of NaCl).

2. Convert 500 mL to liters: $\frac{500}{1000}$.

3. Set up the molarity formula with your values.

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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 find the volume of stock solution needed.

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): $V_1 = \frac{M_2 V_2}{M_1}$

3. Plug in the values and set up the calculation.

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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 geometry, polarity, formal charge, and hybridization.

Key Concepts:

• Lewis Structure: Shows valence electrons and bonds.

• Polarity: Determined by electronegativity and molecular shape.

• Geometry: Use 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. Use VSEPR theory to determine geometry.

4. Calculate formal charge for each atom.

5. Identify hybridization of central atom.

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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 notation.

Key Concepts:

• Electron Configuration: Shows how electrons are distributed among orbitals.

• Noble Gas Notation: Uses the previous noble gas to abbreviate configuration.

• Ions: Adjust electron count for charge.

Step-by-Step Guidance

1. Determine the number of electrons for each atom/ion.

2. Write the full electron configuration.

3. Use noble gas notation to abbreviate.

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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 and distinguish between 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.

2. Write the complete ionic equation by splitting soluble compounds into ions.

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

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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 Ionic Equations

This question tests your ability to write balanced equations and apply solubility rules to determine precipitate formation.

Key Concepts:

• Solubility Rules: Used to predict if a compound will precipitate.

• Net Ionic Equation: Shows only ions involved in forming the precipitate.

Step-by-Step Guidance

1. Write the balanced molecular equation.

2. Apply solubility rules to identify the precipitate.

3. Write the complete ionic equation.

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

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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 and identify oxidation and reduction.

Key Concepts:

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Redox Reaction: Involves transfer of electrons.

Step-by-Step Guidance

1. Write the balanced equation for the reaction.

2. Assign oxidation states to each element.

3. Identify which element is oxidized and which is 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 internal energy change.

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. Set up the calculation for $\Delta U$.

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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 Using Heats of Formation

This question tests your ability to use heats of formation to calculate enthalpy change for a reaction.

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 methane.

2. List the heats of formation for all reactants and products.

3. Multiply each heat of formation by the number of moles in the equation.

4. Set up the calculation using the formula above.

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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: $23.0 \text{ mL} \times 1.00 \text{ g/mL}$

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.

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