Properties Of Acids And Bases (Lab) printable pdf download

Acids/Bases 1

Name ______________________________________________ Date _________ Period ______

Properties of Acids and Bases

Purpose

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Pre-Lab Discussion (Do not copy in your lab book)

The word acid is derived from the Latin verb acere which means “to (be) sour.” The origin of

the word acid reveals a characteristic physical property of acids – they taste sour. Lemons,

oranges, and grapefruits are called citrus fruits because they contain citric acid, an acidic

compound which gives them their sour taste. Strong acids dissociate completely in water to form

ions and are thus strong electrolytes. In contrast, weak acids do not readily dissociate in water—

in fact, less than 1% of the molecules are probably ionized at any given time. Weak acids are

therefore weak electrolytes.

Indicators are organic dyes that change color in acidic or basic solutions. One of the oldest

known acid-base indicators is litmus, a natural dye obtained from lichens. Its use was described

as early as the sixteenth century. Litmus paper, prepared by soaking paper in a solution of the

dye, is often used as a general test for acids and bases. Phenolphthalein is another indicator that

shows a color change as solutions change from acidic (clear) to basic (pink). Universal indicator

and pH paper are two products that use combinations of indicators to rank substances from most

acidic to least acidic, or most basic to least basic.

The pH scale is a numerical scale that is used to describe the relative acidity or basicity of a

ions. The abbreviation pH stands for “power of

solution and is related to the concentration of H

hydrogen” – a difference of one unit on the pH scale corresponds to a power of ten difference in

the concentration of H

ions. Acids and bases are substances that alter the concentrations of H

and OH

ions in solutions.

Base

Acids and bases react with each other to give neutral products – solutions that are neither

acidic nor basic. The products of neutralization of an acid and a base are an ionic compound (a

salt) and water. The amount of acid that will react with a specific amount of base is governed by

stoichiometry. Neutralization reactions are frequently used in the laboratory to determine how

much of an acidic or basic compound is present in a substance.

Properties Of Acids And Bases (Lab)