Chapter 3: Stoichiometry

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Chapter Overview & SLOs

What is stoichiometry? Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It involves calculations using balanced chemical equations.

How do we perform mole calculations? Convert mass to moles using the formula: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar mass (g/mol)}}$.

What is a limiting reactant? The limiting reactant is the reactant that is consumed first in a chemical reaction and determines the maximum amount of product that can be formed. The other reactants are in excess.

How do we identify the limiting reactant? Convert the masses of all reactants to moles, use the stoichiometric ratio from the balanced equation to calculate the required moles, and compare with available moles. The reactant that produces the least amount of product is the limiting reactant.

What is theoretical yield? Theoretical yield is the maximum amount of product that can be formed from the limiting reactant, as calculated by stoichiometry.

What is actual yield? Actual yield is the amount of product actually obtained from a reaction. It is usually less than the theoretical yield.

What is percentage yield? Percentage yield compares the actual yield to the theoretical yield: $\text{Percentage Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$.

Why is the percentage yield rarely 100%? Reasons include incomplete reactions (reversible reactions), unwanted side reactions, product loss during filtration or purification, and measurement errors.

What is an empirical formula? The empirical formula represents the simplest whole-number ratio of atoms of each element in a compound.

How do we determine the molecular formula from the empirical formula? Calculate the empirical formula mass, then find the factor $n = \frac{\text{Molar mass}}{\text{Empirical mass}}$, and multiply the subscripts of the empirical formula by $n$.

What is concentration? Concentration is the amount of solute present in a given volume of solution. It is typically expressed in moles per cubic decimeter (mol/dm³) or molarity (M).

How do we calculate concentration during titration? Use the titration formula $C_1V_1 = C_2V_2$, where $C$ is concentration and $V$ is volume. This is used for acid-base titrations to find unknown concentrations.

Important volume conversion: $1 \text{ dm}^3 = 1000 \text{ cm}^3$. When using volumes in titration calculations, ensure consistent units.

These notes are strictly aligned with the Student Learning Outcomes (SLOs) for the FBISE 2026 annual examination.

• How do we determine the molecular formula from an empirical formula? We calculate the empirical formula mass and find the factor $n = \frac{\text{molar mass}}{\text{empirical mass}}$, then multiply the subscripts of the empirical formula by this factor.
• How do we identify the limiting reactant in a chemical reaction? We convert the masses of all reactants to moles and use the stoichiometric ratio from the balanced equation to compare the required moles against available moles. The reactant that produces the least product is the limiting reactant.
• How do we calculate the percentage yield of a reaction? It is determined using the formula $\text{Percentage Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$, where the theoretical yield is the maximum amount predicted by stoichiometry from the limiting reactant.
• How do we calculate the concentration of a solution during titration? By using the titration formula $C_1V_1 = C_2V_2$ (where $C$ is concentration in mol/dm³ and $V$ is volume in dm³ or cm³, as long as units are consistent) to find the unknown concentration of an acid or base.

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