Q1. What is the Nuclear Theory of the Atom? List the 3 types of subatomic particles, their location in the atom, and their charges.

Background

Topic: Atomic Structure and Subatomic Particles

This question tests your understanding of the basic structure of the atom, the nuclear theory, and the properties of protons, neutrons, and electrons.

Key Terms:

• Nuclear Theory of the Atom: A model describing the atom as having a dense central nucleus containing protons and neutrons, with electrons in the surrounding space.

• Proton (p+): Positively charged particle in the nucleus.

• Neutron (n0): Neutral particle in the nucleus.

• Electron (e–): Negatively charged particle outside the nucleus.

Step-by-Step Guidance

1. Start by recalling the main points of the nuclear theory: the atom has a small, dense nucleus, most of the atom's mass is in the nucleus, and the nucleus contains protons and neutrons.

2. List the three subatomic particles: protons, neutrons, and electrons.

3. For each particle, state its location (nucleus or outside nucleus) and its charge (positive, negative, or neutral).

4. Organize your answer in a clear format, such as a table or bullet points, to show the particle, location, and charge.

Try summarizing the nuclear theory and listing the particles before checking the answer!

Q2. How many protons, neutrons, and electrons are in the following? Assign A and Z for each.

• a) 207Pb

• b) Be–9

• c) 81Br– (hint: this is a charged isotope)

Background

Topic: Isotopes and Subatomic Particle Counting

This question tests your ability to determine the number of protons, neutrons, and electrons in isotopes and ions, and to assign mass number (A) and atomic number (Z).

Key Terms and Formulas:

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons ().

• Isotope: Atoms of the same element (same Z) with different numbers of neutrons (different A).

• Ion: Atom with a net charge due to loss or gain of electrons.

Step-by-Step Guidance

1. Identify the element from its symbol (e.g., Pb is lead, Br is bromine, Be is beryllium).

2. Find the atomic number (Z) for each element using the periodic table.

3. For each isotope, the mass number (A) is given (e.g., 207 in 207Pb).

4. Calculate the number of neutrons: .

5. For ions, adjust the number of electrons: electrons = Z - (charge). For anions (negative charge), add electrons; for cations (positive charge), subtract electrons.

Try filling in the numbers for each isotope before checking the answer!

Q3. Naturally occurring magnesium is composed of 78.99% 24Mg (atomic mass= 23.9850 amu), 10.00% of 25Mg (atomic mass= 24.9858 amu), and 11.01% 26Mg (atomic mass= 25.9826 amu). Calculate the average atomic mass of magnesium.

Background

Topic: Average Atomic Mass Calculation

This question tests your ability to calculate the weighted average atomic mass of an element based on the relative abundances and atomic masses of its isotopes.

Key Formula:

Step-by-Step Guidance

1. Convert each percent abundance to a decimal (fractional abundance) by dividing by 100.

2. Multiply each isotope's mass by its fractional abundance.

3. Add the results for all isotopes to get the average atomic mass.

4. Set up the calculation clearly, showing each multiplication and the sum.

Try setting up the calculation before checking the answer!

Q4. Aqueous lead (II) nitrate reacts with aqueous cesium chloride.

Background

Topic: Double Displacement Reactions, Nomenclature, Stoichiometry

This multi-part question tests your ability to write and balance chemical equations, predict products, apply solubility rules, classify compounds and reactions, and perform stoichiometric calculations.

Key Terms and Concepts:

• Double Displacement Reaction: Two compounds exchange ions to form two new compounds.

• Solubility Rules: Guidelines to predict if a compound is soluble (aq) or insoluble (s).

• Molar Mass: Mass of one mole of a substance (g/mol).

• Avogadro's Number: particles/mol.

• Mass Percent:

Step-by-Step Guidance (for selected subparts)

1. Write the formulas for the reactants: Lead(II) nitrate is Pb(NO3)2, cesium chloride is CsCl.

2. Predict the products: Swap the cations and anions to form PbCl2 and CsNO3. Assign phases using solubility rules.

3. Balance the equation: Make sure the number of atoms of each element is the same on both sides.

4. For molar mass calculations: Add up the atomic masses of all atoms in each formula.

5. For mole and molecule conversions: Use the relationships:

6. For ions in a sample: Multiply the number of formula units by the number of each ion per formula unit.

Try writing the balanced equation and setting up the calculations before checking the answer!

Q5. PCl5 (s) + H2O (l) → H3PO4 (aq) + HCl (aq)

Background

Topic: Balancing Equations, Nomenclature, Stoichiometry

This question covers balancing chemical equations, naming compounds, classifying compound types, and performing mass and mole calculations.

Key Concepts and Formulas:

• Balancing Equations: Ensure the same number of each atom on both sides.

• Molar Mass: Add atomic masses for each atom in the formula.

• Conversions:

Step-by-Step Guidance (for selected subparts)

1. Balance the equation by adjusting coefficients so that the number of each atom is equal on both sides.

2. Name each compound using IUPAC rules (e.g., phosphorus pentachloride, water, phosphoric acid, hydrogen chloride).

3. Calculate the molar mass of each compound by summing the atomic masses.

4. For mass and mole conversions, use the relationships above.

5. For number of atoms, multiply the number of molecules by the number of that atom per molecule.

Try balancing the equation and setting up the calculations before checking the answer!

Q6. Solid lithium carbonate reacts with phosphoric acid.

Background

Topic: Reaction Types, Stoichiometry, Mass Percent

This question involves writing and balancing a chemical equation, classifying the reaction, and performing stoichiometric and mass percent calculations.

Key Concepts and Formulas:

• Balancing Equations: Adjust coefficients for atom balance.

• Stoichiometry: Use mole ratios from the balanced equation.

• Mass Percent:

Step-by-Step Guidance (for selected subparts)

1. Write the formulas for lithium carbonate (Li2CO3) and phosphoric acid (H3PO4).

2. Predict the products and write the unbalanced equation.

3. Balance the equation by adjusting coefficients.

4. Convert given masses to moles using molar mass.

5. For number of molecules or atoms, use Avogadro's number and the stoichiometry of the compound.

Try writing and balancing the equation before checking the answer!

Q7. Stoichiometry Practice: NaOH (aq) + CuBr2 (aq) → Cu(OH)2 (s) + NaBr (aq)

Background

Topic: Stoichiometry Calculations

This question tests your ability to use balanced equations and stoichiometric relationships to convert between grams, moles, and molecules of reactants and products.

Key Concepts and Formulas:

• Molar Mass: Used to convert between grams and moles.

• Stoichiometric Ratios: Use coefficients from the balanced equation.

• Avogadro's Number: particles/mol.

Step-by-Step Guidance (for first subpart)

1. Write and balance the chemical equation.

2. Convert the given mass of NaOH to moles using its molar mass.

3. Use the stoichiometric ratio from the balanced equation to find moles of Cu(OH)2 formed.

4. Set up the calculation, but stop before multiplying out the final value.

Try setting up the stoichiometry before checking the answer!

Try solving on your own before revealing the answer!