Vocabulary Standard 5  Acids and Bases






([Lat. acidus, sour])

1. a compound which releases hydrogen ions (H+) in solution (Arrhenius). 2. a compound containing detachable hydrogen ions (Bronsted-Lowry). 3. a compound that can accept a pair of electrons from a base (Lewis)..

Acid-base indicators


A weak acid that has acid and base forms with sharply different colors. Changes in pH around the acid's pKa are "indicated" by color changes.



A substance that can act as either an acid or a base in a reaction. For example, aluminum hydroxide can neutralize mineral acids ( Al(OH)3 + 3 HCl = AlCl3 + 3 H2O ) or strong bases ( Al(OH)3 + 3 NaOH = Na3AlO3 + 3 H2O).

Arrhenius acid


A compound which releases hydrogen ions (H+) in solution

Arrhenius base


a substance which acts as a proton (H+) acceptor

Brønsted-Lowry acid


a compound containing detachable hydrogen ions

Brønsted-Lowry base


A material that accepts hydrogen ions in a chemical reaction.

Buffer solution


A solution that can maintain its pH value with little change when acids or bases are added to it. Buffer solutions are usually prepared as mixtures of a weak acid with its own salt or mixtures of salts of weak acids. For example, a 50:50 mixture of 1 M acetic acid and 1 M sodium acetate buffers pH around 4.7.

Conjugate acid


substance formed when a base gains a hydrogen ion. Considered an acid because it can lose a hydrogen ion to reform the base

Conjugate base


substance formed when an acid loses a hydrogen ion. Considered a base because it can gain a hydrogen ion to reform the acid.

dissociation   When water dissolves a compound.

End point


The experimental estimate of the equivalence point in a titration.

Equivalence point


The equivalence point is the point in a titration when enough titrant has been added to react completely with the analyte

hydrogen ion    

Hydronium ion


The H3O+ ion, formed by capture of a hydrogen ion by a water molecule. A strong covalent bond is formed between the hydrogen ion and water oxygen; all hydrogen ions in aqueous solution are bound inside hydronium ions.

hydroxide   The OH- ion, made famous by bases.
Indicator   A compound that turns different colors at different pH values.  We generally like to have the color change at a pH of around seven because that's where the equivalence point of a titration is.

Ionic Dissociation


When ionic substances dissolve, their ions are surrounded by solvent molecules and separated from each other. This phenomena is also called ionization.

Lewis acid


A compound that can accept a pair of electrons from a base

litmus paper    



A chemical change in which one compound acquires H+ from another. The compound that receives the hydrogen ion is the base; the compound that surrenders it is an acid.



pH is a measure of effective concentration of hydrogen ions in a solution. It is approximately related to the molarity of H+ by pH = - log [H+]

pH meter


An electric device that measures pH using an electrochemical cell.



An expression of the alkalinity of a solution; the negative logarithm of the hydroxyl-ion concentration.



a compound formed by replacing hydrogen in an acid by a metal (or a radical that acts like a metal)

Standard solution


A solution of known molarity is called a standard solution. Its concentration is determined by a process known as standardization. If you have a primary standard (a compound which is very pure, stable, nonhygroscopic, and with a high molecular weight) you can prepare a standard solution simply by dissolving a known amount of the compound in a known volume of liquid. If you don't have such a compound, you'll have to standardize your solution against a primary standard. For example, you can standardize a silver nitrate solution by using it to titrate NaCl, which is a primary standard.

Strong Acid   An acid that fully dissociates in water
Strong Base   An base that fully dissociates in water



A procedure for determining the amount of some unknown substance (the analyte) by quantitative reaction with a measured volume of a solution of precisely known concentration (the titrant).

universal indicator    

Weak acid


An acid that only partially dissociates into hydrogen ions and anions in solution. Weak acids are weak electrolytes. Recognize weak acids by learning the six common strong acids; any acid that doesn't appear on the list of strong acids is usually a weak acid.

Weak base