1 - Stoichiometry

We do exactly two things in AP chemistry. Stoichiometry and Coulombic attractions. This unit is the mathematical foundation of almost everything else we will do this year. Your determined mindset to learn, understand and apply the fundamentals of stoichiometry will be rewarded in nearly every unit of learning. Two pencils and maximum effort.

AP Chem Unit 2 Stoichiometry Outline and Objectives.docx

Mole Unit & Conversions

Avogadro’s number provides the connection between the number of moles in a pure sample of a substance and the number of constituent particles (or units) of that substance.
Thus, for any sample of a pure substance, there is a specific numerical relationship between the molar mass of the substance, the mass of the sample, and the number of particles (or units) present.
The number of atoms, molecules, or formula units in a given mass of substance can be calculated.

The mole and Avogadro's numberOne mole of a substance is equal to 6.022 × 10^23 units of that substance (such as atoms, molecules, or ions). The number 6.022 × 10^23 is known as Avogadro's number or Avogadro's constant. The mole can be used to convert between atomic mass units and grams.

Molecular Composition

Mass Percent

An empirical formula is the lowest whole number ratio of atoms in a compound. Two molecules of the same elements with identical mass percent of their constituent atoms will have identical empirical formulas.
Because pure compounds have a specific mass percent of each element, experimental measurements of mass percents can be used to verify the purity of compounds.

Empirical, molecular, and structural formulasExamples to demonstrate the difference between empirical, structural, and molecular formulas

Combustion Analysis

Combustion is the exothermic reaction of a hydrocarbon with oxygen to form carbon dioxide and water.
The empirical and molecular formula of a hydrocarbon is determined from experimental results obtaining the mass of carbon dioxide and water formed from combustion.
The molecular formula of a hydrocarbon is determined given the molecular mass of the hydrocarbon and the results of combustion analysis.

Equation Writing & Types of Reactions

Atoms and molecules interact with one another on the atomic level. Balanced chemical equations give the number of particles that react and the number of particles produced. Because of this, expressing the amount of a substance in terms of the number of particles, or moles of particles, is essential to understanding chemical processes.
The subscripts in a chemical formula represent the number of atoms of each type in a molecule.
The coefficients in a balanced chemical equation represent the relative numbers of particles that are consumed and created when the process occurs.
The concept of conservation of atoms plays an important role in the interpretation and analysis of many chemical processes on the macroscopic scale.

Dissolution and precipitationDefining solute, solvent, hydration, dissolution, precipitation, net ionic equation, and spectator ions. Looking at the molecular level interactions between water and ions in NaCl.

Stoichiometry

The concept of conservation of atoms plays an important role in the interpretation and analysis of many chemical processes on the macroscopic scale.
In gravimetric analysis, a substance is added to a solution that reacts specifically with a dissolved analyte (the chemical species that is the target of the analysis) to form a solid. The mass of solid formed can be used to infer the concentration of the analyte in the initial sample.

StoichiometryStoichiometry expresses the quantitative relationship between reactants and products in a chemical equation. Stoichiometric coefficients in a balanced equation indicate molar ratios in that reaction. Stoichiometry allows us to predict certain values, such as the percent yield of a product or the molar mass of a gas.

Limiting Reactant Stoichiometry

Coefficients of balanced chemical equations contain information regarding the proportionality of the amounts of substances involved in the reaction.
These values can be used in chemical calculations that apply the mole concept; the most important place for this type of quantitative exercise is the laboratory. 1. Calculate amount of product expected to be produced in a laboratory experiment. 2. Identify limiting and excess reactant; calculate percent and theoretical yield for a given laboratory experiment.

Stoichiometry: Limiting reagentStoichiometry problem where we find the limiting reagent and calculate grams of product formed.

Extra Stoichiometry Instructional Videos

Here's another Melissa Maribel playlist for concepts related to stoichiometry. If the Khan Academy videos are too slow or don't work for you, give Melissa's videos a try. Bookmark this playlist! You will most likely want to refer back to it often over the course of the year, especially for midterm review.