# 4: Chemical Reactions and Aqueous Reactions

• 4.1: Global Warming and the Combustion of Fossil Fuels
• 4.2: How Much Carbon Dioxide?
A balanced chemical equation may be used to describe a reaction’s stoichiometry (the relationships between amounts of reactants and products). Coefficients from the equation are used to derive stoichiometric factors that subsequently may be used for computations relating reactant and product masses, molar amounts, and other quantitative properties.
• 4.3: Limiting Reactant, Theoretical Yield, and Percent Yield
The stoichiometry of a balanced chemical equation identifies the maximum amount of product that can be obtained. The stoichiometry of a reaction describes the relative amounts of reactants and products in a balanced chemical equation. A stoichiometric quantity of a reactant is the amount necessary to react completely with the other reactant(s). If a reactant remains unconsumed after complete reaction has occurred, it is in excess. The reactant that is consumed first is the limiting reagent.
• 4.4: Solution Concentration and Solution Stoichiomentry
Solution concentrations are typically expressed as molarities and can be prepared by dissolving a known mass of solute in a solvent or diluting a stock solution. The concentration of a substance is the quantity of solute present in a given quantity of solution. Concentrations are usually expressed in terms of molarity, defined as the number of moles of solute in 1 L of solution.
• 4.5: Types of Aqueous Solutions and Solubility
Electrolytic solutions are those that are capable of conducting an electric current. A substance that, when added to water, renders it conductive, is known as an electrolyte. A common example of an electrolyte is ordinary salt, sodium chloride. Solid NaCl and pure water are both non-conductive, but a solution of salt in water is readily conductive. A solution of sugar in water, by contrast, is incapable of conducting a current; sugar is therefore a non-electrolyte.
• 4.6: Precipitation Reactions
A complete ionic equation consists of the net ionic equation and spectator ions. Predicting the solubility of ionic compounds gives insight into feasibility of reactions occuring. The chemical equation for a reaction in solution can be written in three ways. The overall chemical equation shows all the substances in their undissociated forms; the complete ionic equation shows substances in the form in which they actually exist in solution; and the net ionic equation omits all spectator ions.
• 4.7: Representing Aqueous Reactions- Molecular, Ionic, and Complete Ionic Equations
The chemical equation for a reaction in solution can be written in three ways. The overall chemical equation shows all the substances present in their undissociated forms; the complete ionic equation shows all the substances present in the form in which they actually exist in solution; and the net ionic equation is derived from the complete ionic equation by omitting all spectator ions, ions that occur on both sides of the equation with the same coefficients.
• 4.8: Acid-Base and Gas-Evolution Reactions
An acidic solution and a basic solution react together in a neutralization reaction that also forms a salt. Acid–base reactions require both an acid and a base. In Brønsted–Lowry terms, an acid is a substance that can donate a proton and a base is a substance that can accept a proton. Acids also differ in their tendency to donate a proton, a measure of their acid strength. The acidity or basicity of an aqueous solution is described quantitatively using the pH scale.
• 4.9: Oxidation-Reduction Reactions
Oxidation–reduction reactions are balanced by separating the overall chemical equation into an oxidation equation and a reduction equation. In oxidation–reduction reactions, electrons are transferred from one substance or atom to another. We can balance oxidation–reduction reactions in solution using the oxidation state method, in which the overall reaction is separated into an oxidation equation and a reduction equation. The outcome of these reactions can be predicted using the activity series.
• 4.10: Acids- Properties and Examples
Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food. Acids are a distinct class of compounds because of the properties of their aqueous solutions.
• 4.11: Bases- Properties and Examples
A base is thought of as a substance which can accept protons, or any chemical compound that yields hydroxide ions (OH-) in solution. It is also commonly referred to as any substance that can react with an acid to decrease or neutralize its acidic properties, change the color of indicators (e.g. turn red litmus paper blue), feel slippery to the touch when in solution, taste bitter, react with acids to form salts, and promote certain chemical reactions (e.g. base catalysis).
• 4.12: Molecular Definitions of Acids and Bases
Although the properties of acids and bases had been recognized for a long time, it was Svante Arrhenius in the 1880s who determined that the properties of acids were due to the presence of hydrogen ions, and that the properties of bases were due to the presence of hydroxide ions.
• 4.13: Reactions of Acids and Bases
When an acid and a base are combined, water and a salt are the products. Salts are ionic compounds containing a positive ion other than H+ and a negative ion other than the hydroxide ion, OH-. Double displacement reactions of this type are called neutralization reactions. Salt solutions do not always have a pH of 7, however. Through a process known as hydrolysis, the ions produced when an acid and base combine may react with the water to produce slightly acidic or basic solutions.
• 4.14: Strong and Weak Acids and Bases
Acids are classified as either strong or weak, based on their ionization in water. A strong acid is an acid which is completely ionized in an aqueous solution. A weak acid is an acid that ionizes only slightly in an aqueous solution. Acetic acid (found in vinegar) is a very common weak acid.
• 4.15: Water - Acid and Base in One
Water is an interesting compound in many respects. Here, we will consider its ability to behave as an acid or a base. In some circumstances, a water molecule will accept a proton and thus act as a Brønsted-Lowry base.
• 4.16: The pH and pOH Scales - Ways to Express Acidity and Basicity
pH and pOH are defined as the negative log of hydrogen ion concentration and hydroxide concentration, respectively. Knowledge of either can be used to calculate either [H+] of [OH-]. pOH is related to pH and can be easily calculated from pH.
• 4.17: Acid–Base Titration
Acid-base titrations are lab procedures used to determine the concentration of a solution. One of the standard laboratory exercises in General Chemistry is an acid-base titration. During an acid-base titration, an acid with a known concentration (a standard solution) is slowly added to a base with an unknown concentration (or vice versa). A few drops of indicator solution are added to the base. The indicator will signal, by color change, when the base has been neutralized (when [H+] = [OH-]).

Thumbnail: Copper from a wire is displaced by silver in a silver nitrate solution it is dipped into, and solid silver precipitates out. (CC BY-SA 3.0 au; Toby Hudson via Wikipedia).