Stoichiometry and Solution Calculations

Stoichiometry Fundamentals

• Stoichiometry is the quantitative relationship between reaction components.
• Balanced equation coefficients indicate the molar ratio (e.g., $2\,mol$ of aluminum to $3\,mol$ of iodine).
• Coefficients are exact values and do not impact significant figures calculations.

Mass and Molar Conversions

• To calculate the mass of product or reactant needed:

1. Convert the starting mass to moles using molar mass ($g\,mol^{-1}$).
2. Multiply by the molar ratio from the chemical equation.
3. Convert the resulting moles of the second substance to mass using its molar mass.

• Example: Calculating product yielded from $3.21\,g$ of aluminum ($Al$) and an excess of iodine ($I_2$).

Limiting Reactants

• A limiting reactant problem occurs when starting amounts for multiple reactants are provided.
• The limiting reactant is the one capable of producing the least amount of product; it is consumed entirely and dictates the reaction's end.
• Data example: While $50\,g$ of $Al$ could produce $756\,g$ of product, a limited supply of $I_2$ only allows for the formation of $53.5\,g$ of $AlI_3$. Therefore, $I_2$ is the limiting reactant.

Solution Stoichiometry and Titrations

• For reactions in solution, chemistry calculations use concentration (molarity) instead of mass.
• Molarity ($mol\,dm^{-3}$) is defined as moles of solute per $dm^3$ of solution.
• Moles of a solute are determined by multiplying the molarity by the volume: $Molarity \times Volume(dm^3) = Moles$.
• Titration process:

1. Titrant (known concentration) is added to an analyte (unknown concentration).
2. Calculate moles of titrant used (e.g., $23.4\,cm^3$ of $0.5\,mol\,dm^{-3}$ $NaOH$).
3. Use the molar ratio to determine the moles of analyte (e.g., $0.00585\,mol$ of $H_2SO_4$).
4. Divide analyte moles by the analyte volume in $dm^3$ to find the concentration.