Chapter 3: Molecules, Moles, and Chemical Equations — Key Concepts and Formulas

Flashcards covering fundamental concepts from Chapter 3: molarity, molar mass, Avogadro’s number, empirical and molecular formulas, solution chemistry, electrolytes, and balancing/writing chemical equations.

What is a mole and how is Avogadro’s number defined?

A mole is the amount of substance that contains Avogadro’s number of particles; Avogadro’s number is 6.022 × 10^23 particles per mole.

How is the molar mass of a compound determined from its chemical formula?

Add up the atomic masses of all atoms in the formula, multiplying by their subscripts; for atoms inside parentheses, multiply by both the inner and outer subscripts.

What is the relationship between mass, moles, and molar mass?

Moles = mass / molar mass; molar mass links a given mass to the number of moles.

Why is molar mass essential for converting between mass and moles?

Because it provides the conversion factor that translates grams into moles and vice versa, based on conservation of mass.

What is the practical use of Avogadro’s number in chemistry?

It provides a convenient scale for counting particles; one mole contains the same number of particles for any substance.

What is the purpose of balancing a chemical equation?

To satisfy the law of conservation of matter by ensuring the same number of atoms of each element appear on both sides.

What does a stoichiometric coefficient represent in a balanced equation?

The number of particles (molecules/ions) of a given species involved in the reaction.

What are the three forms of chemical equations used for reactions in solution?

Molecular, total ionic, and net ionic equations.

What is an electrolyte, and how do strong and weak electrolytes differ?

An electrolyte dissociates or ionizes in water to produce ions and conduct electricity; strong electrolytes dissociate completely, while weak electrolytes dissociate only partially.

What is the Arrhenius definition of acids and bases?

Acids produce H+ (hydronium) ions in water; bases produce OH− ions in water.

What is a neutralization reaction?

An acid reacts with a base to form water and a salt.

What is a precipitation reaction?

A reaction in which an insoluble solid (precipitate) forms from aqueous solutions.

What is molarity and how is it defined?

Molarity (M) = moles of solute per liter of solution.

How can you relate volume, molarity, and moles in a solution?

Moles = M × volume (in liters); volume = moles / M; dilution can be described by M1V1 = M2V2.

What happens to the amount of solute during a dilution?

The number of moles of solute remains constant; only the solvent amount changes, lowering the concentration.

What is an empirical formula?

The simplest whole-number ratio of atoms in a compound derived from percent composition and molar masses.

How do you determine a molecular formula from an empirical formula?

If the molar mass of the compound is known, multiply the empirical formula by a factor (molar mass divided by empirical formula mass) to obtain the molecular formula.

What is the difference between mass percent and mole percent in alloys?

Mass percent uses mass fractions; mole percent uses mole fractions; conversions require molar masses.

How does isotopic abundance affect molar mass?

Molar mass is a weighted average that accounts for natural isotopic abundances listed on the periodic table.

What is the connection between Avogadro’s number and the mass of a mole?

One mole of a substance has a mass in grams numerically equal to its molar mass in g/mol; this links mass and moles.

What does the symbol (aq) indicate in chemical equations and what are the other common state symbols?

(aq) means dissolved in water (aqueous); (s) solid, (l) liquid, (g) gas.

What are solvents, solutes, and solutions?

In a solution, the solvent is the component in greatest amount; solutes are the dissolved substances; the solution is the homogeneous mixture of solute in solvent.