Q1. How many gold atoms are there in 9.67 g of gold?

Background

Topic: The Mole Concept & Dimensional Analysis

This question tests your ability to convert between mass, moles, and the number of atoms using the molar mass and Avogadro's number.

Key Terms and Formulas:

• Molar mass: The mass (in grams) of one mole of a substance. For gold (Au), it is 196.967 g/mol.

• Avogadro's number: atoms/mol

• Dimensional analysis: A method to convert units stepwise.

Key formula:

Step-by-Step Guidance

1. Identify the mass of gold given: .

2. Find the molar mass of gold: .

3. Set up the conversion from grams to moles: .

4. Use Avogadro's number to convert moles to atoms: .

5. Multiply the values to find the number of atoms, keeping track of significant figures.

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Q2. What is the mass of lead (Pb) atoms?

Background

Topic: The Mole Concept & Mass-Atom Conversions

This question tests your ability to convert from the number of atoms to mass using Avogadro's number and the molar mass of lead.

Key Terms and Formulas:

• Avogadro's number: atoms/mol

• Molar mass of lead (Pb):

Key formula:

Step-by-Step Guidance

1. Start with the number of lead atoms: atoms.

2. Convert atoms to moles: .

3. Multiply the number of moles by the molar mass of lead: g/mol.

4. Set up the calculation so that atoms cancel, leaving grams as the final unit.

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Q3. Calculate the mass, in grams, of a single iodine atom ( g/mol).

Background

Topic: Atomic Mass and Single Atom Calculations

This question tests your ability to use the atomic mass and Avogadro's number to find the mass of a single atom.

Key Terms and Formulas:

• Atomic mass of iodine: g/mol

• Avogadro's number: atoms/mol

Key formula:

Step-by-Step Guidance

1. Start with the atomic mass of iodine: g/mol.

2. Recognize that 1 mole contains atoms.

3. Set up the calculation: .

4. Ensure the units are correct: grams per atom.

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Q4. Which of the following would you expect to be a molecule and which would you expect to be part of an ionic solid?

Background

Topic: Ionic vs. Covalent Bonding

This question tests your understanding of the difference between molecular (covalent) and ionic compounds, based on the types of elements involved.

Key Terms:

• Covalent bond: A bond formed by sharing electrons between two nonmetals.

• Ionic bond: A bond formed by transferring electrons from a metal to a nonmetal, resulting in oppositely charged ions.

• Molecule: A cluster of atoms held together by covalent bonds.

• Ionic solid: A lattice of ions held together by ionic bonds.

Step-by-Step Guidance

1. Identify whether the compound is made of metals, nonmetals, or both.

2. Recall that covalent bonds form between two nonmetals, resulting in molecules.

3. Recall that ionic bonds form between a metal and a nonmetal, resulting in ionic solids.

4. Classify each compound based on the elements present.

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