Empirical and Molecular Formulae

Empirical Formula: This is the simplest, most reduced ratio of atoms in a compound. For instance, the empirical formula of glucose (which has 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms), is CH2O.
Molecular Formula: Unlike the empirical formula, the molecular formula shows the actual number of each type of atom in a molecule of the compound. Using the previous example, the molecular formula of glucose is C6H12O6.
Converting Empirical to Molecular Formula: If the molar mass of the molecular compound is known, along with the empirical formula, you can determine the molecular formula. First, find the molar mass of the empirical formula, and then divide the molar mass of the molecular compound by the molar mass of the empirical formula to find the ratio. Multiply the subscripts in the empirical formula by this ratio to get the molecular formula.
Finding Empirical Formula from Mass: If the mass of each element in a compound is known, you can find the empirical formula by converting the mass of each element to moles. After that, divide each by the smallest number of moles, and round to the nearest whole number.
Finding Empirical Formula from Percentage Composition: To find the empirical formula from percentage composition, assume a 100g sample, so the percentages become grammes. Convert grammes to moles, divide by the smallest number of moles and round to the nearest whole number.
Balancing Chemical Equations: This is done by ensuring the number of atoms for each element is the same on both sides of the equation.
Mole Calculations: One mole of a substance is equivalent to its relative formula mass in grammes. The number of moles = mass in g / relative formula mass.
Avogadro’s Constant: The number of atoms, molecules or ions in a mole of a substance is always constant, at around 6.02 x 10^23, known as Avogadro’s Constant.
Stoichiometry: This is the ratio of moles of each substance in a balanced chemical equation. Using stoicheiometry, you can calculate the amounts of reactants needed or products formed in a reaction.
Reagents: These are substances that cause a chemical reaction. When two reagents are used, one is often used in excess to ensure the other is fully reacted.
Limiting Reagent: This is the reagent that is completely consumed in a chemical reaction. It effectively dictates when the reaction stops.
Yield: This is the amount of product formed from a chemical reaction. Actual yield refers to the amount actually produced, while theoretical yield is the maximum amount of product that could have been produced.
Percent Yield: This is calculated by the formula: Actual yield / Theoretical yield x 100%.
Atom Economy: A measure of the proportion of reactants that becomes useful products. The higher the atom economy, the greener the process. Calculated by: (relative formula mass of desired products / relative formula mass of all products) x 100%.
Concentration: The amount of a specified substance in a unit amount of another substance, often expressed in moles per dm^3.
Solutions and Titrations: A titration is a method used to determine the concentration of a solution by neutralising it with a standard solution of known concentration. Molarity is a common unit of concentration, measured in moles/dm^3.