Summary
The mole is a unit used to express the amount of a substance, defined by the number of entities in 12 grams of carbon-12, approximately 6.02 x 10^23 entities per mole. Molar Mass — the mass of one mole of a substance in grams. Example: The molar mass of water (H2O) is 18.015 g/mol. Stoichiometry — calculations involving the quantities of reactants and products in a chemical reaction. Example: Using mole ratios to determine the amount of reactants needed. Limiting Reagent — the reactant that is completely consumed first, limiting the amount of product formed. Example: In a reaction between sodium and sulfur, sodium can be the limiting reagent. Empirical Formula — the simplest whole number ratio of elements in a compound. Example: For glucose (C6H12O6), the empirical formula is CH2O.
Exam Tips
Key Definitions to Remember
- The mole is a unit of measurement for the amount of substance.
- Avogadro's constant is approximately 6.02 x 10^23 entities per mole.
- Molar mass is the mass of one mole of a substance in grams.
Common Confusions
- Confusing molar mass with molecular mass.
- Misunderstanding the concept of limiting reagents.
Typical Exam Questions
- What is the molar mass of water? 18.015 g/mol
- How do you calculate the number of moles from mass and molar mass? Use n = m / Mr
- What is the empirical formula of a compound with 68% carbon, 9% hydrogen, and 23% oxygen? CH2O
What Examiners Usually Test
- Understanding of mole calculations and conversions.
- Ability to identify and calculate limiting reagents.
- Proficiency in determining empirical and molecular formulas.