Summary
In this topic, you will learn about different types of chemical formulae and how to calculate them, including molecular and empirical formulae. You will also understand the concept of the mole and Avogadro's constant, as well as the differences between elements, mixtures, and compounds.
- Elements — Substance made from only one type of atom Example: Carbon (C)
- Compounds — Substance made from two or more elements that undergoes chemical reaction with each other Example: Water (H2O)
- Mixtures — Substances made by mixing two or more elements or compounds (no chemical reaction) Example: Air
- Molecular Formula — The actual number of atoms of each element present in a single molecule of the compound Example: C6H12O6 for glucose
- Empirical Formula — The simplest whole number ratio of the elements present in the compound Example: CH2O for glucose
- The Mole — A unit of measurement used to express the amount of a substance, defined as containing 6.02 x 10^23 entities Example: 1 mole of carbon-12 weighs 12 grams
- Avogadro's Constant — The number of entities in a mole, approximately 6.02 x 10^23 entities per mole Example: 1 mole of any substance contains 6.02 x 10^23 atoms or molecules
Exam Tips
Key Definitions to Remember
- Element: Substance made from only one type of atom
- Compound: Substance made from two or more elements that undergoes chemical reaction
- Mixture: Substances made by mixing two or more elements or compounds without chemical reaction
- Molecular Formula: Actual number of atoms of each element in a molecule
- Empirical Formula: Simplest whole number ratio of elements in a compound
- Mole: Unit of measurement for amount of substance
- Avogadro's Constant: Number of entities in a mole, approximately 6.02 x 10^23
Common Confusions
- Confusing molecular formula with empirical formula
- Misunderstanding the concept of the mole and Avogadro's constant
Typical Exam Questions
- What is the molecular formula of a compound with an empirical formula of CH2 and a molar mass of 56 g/mol? Answer: C4H8
- How do you calculate the empirical formula from mass data? Answer: Convert mass to moles, then find the simplest whole number ratio
- What is Avogadro's constant? Answer: Approximately 6.02 x 10^23 entities per mole
What Examiners Usually Test
- Ability to calculate molecular and empirical formulae
- Understanding of the differences between elements, mixtures, and compounds
- Application of the mole concept and Avogadro's constant