Unit 12: Acids and Bases

Bronsted--Lowry acids and bases

A Bronsted-Lowry acid is defined as anything that releases H+ ions; a Bronsted-Lowry base is defined as anything that accepts H+ ions. The Bronsted-Lowry concept is based on the transfer of a proton from one substance to another. Any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.

base

A base is a chemical species that donates electrons or hydroxide ions (OH-) or that accepts protons. Bases produce OH- ions in aqueous solutions. Above 7 on the pH scale. Turns red litmus paper blue.

Precipitation reaction

A chemical reaction where one of the products is a precipitate.

Hydronium ion

A hydrogen ion bonded to a molecule of water, H 3 O + , the form in which hydrogen ions are found in aqueous solution. Also called oxonium ion.

Hydroxide ion

A hydroxide is an ion containing one oxygen and one hydrogen atom. The chemical formula for the hydroxide ion is OH-.

pH

A measure of the acidity or basicity of an aqueous solution. pH is a measure of hydrogen ion concentration;

Acid-Base reaction

A reaction between an acid and a base that produces a salt and water.

Arrhenius acids and bases

An Arrhenius acid is a substance that when added to water increases the concentration of H+ ions present. The chemical formulas of Arrhenius acids are written with the acidic hydrogens first. An Arrhenius base is a substance that when added to water increases the concentration of OH- ions present. HCl is an example of an Arrhenius acid and NaOH is an example of an Arrhenius base.

acid

An acid is a chemical species that donates protons or hydrogen ions (H+) and/or accepts electrons. Below 7 on the pH scale. Turns blue litmus paper red

Oxidation reduction reaction

Any chemical reaction in which the oxidation numbers (oxidation states) of the atoms are changed. Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number. Usually the change in oxidation number is associated with a gain or loss of electrons.

Standard solution

Any solution which has a precisely known concentration of solute.

Lewis Acids and Bases

In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. A Lewis acid is therefore any substance, such as the H+ ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the OH- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor.

neutralization

Reaction between an acid and a base which produces a neutral solution (pH = 7).

salt

Salts are ionic compounds that result from the neutralization reaction of an acid and a base.

Dissociation constant

The equilibrium constant of the dissociation reaction of an acid and is denoted by Ka.

Titration

The process in which one solution is added to another solution such that it reacts under conditions in which the added volume may be accurately measured. Titrations are most commonly associated with acid-base reactions. A solution of unknown concentration is reacted with a solution of a known concentration in order to find out more about the unknown solution.

Ionization constant of water

Water molecules can function as both acids and bases. One water molecule (acting as a base) can accept a hydrogen ion from a second one (acting as an acid). A hydronium ion and a hydroxide ion are formed. The hydronium ion is a very strong acid, and the hydroxide ion is a very strong base. As fast as they are formed, they react to produce water again. The net effect is that an equilibrium is set up. At standard temperature and pressure, STP, the equilibrium constant of water, Kw, is equal to Kw= [H30+][OH-] Kw=[1.0x10-7][1.0x10-7] Kw=1.0x10-14

pOH

pOH is a measure of hydroxide ion (OH-) concentration. pOH is a measure of the alkalinity of a solution.