The Chemicals in Your Life
April 5, 1995
Acids and Bases
Chapter 7

ACIDS

donate protons to water to form hydronium ions
taste sour
turn cabbage juice red
turn litmus paper red

BASES

donate hydroxyl groups
accept protons
taste bitter
feel slimey
turn cabbage juice yellow, green or blue depending upon the solution concentration
turn litmus paper blue

pH

The concentration of hydrogen ions is measured on a logrithmic scale: pH = - log [H₃O⁺]. Table 1 shows the correlation between hydrogen ion concentration and pH. A solution with a low pH is acidic, and a solution with a high pH is basic. Solutions at a pH of 7 are neutral.

Recipe for Cabbage juice:

fill a blender with pieces of red (purple) cabbage
add water
blend to smithereens
filter cabbage juice using a coffee filter

The juice can be used to make a rainbow of colors corresponding to various (approximate) pH values.

Strong acids and bases completely dissociate to form ionic species. There is none of the original acid or base left in solution. Weak acids and bases only partially dissociate to form some ions and there is still some of the original acid or base present in solution. For example, a .1M solution of HCl has a pH of 1, because all of the HCl reacts with water to form H₃O⁺ ions. Therefore all the moles that were once HCl are now H₃O⁺ ions and we can detect them using a pH meter. In contrast, acetic acid is a weak acid and it only partially dissociates to form some hydronium ions while some acetic acid molecules remain intact. The pH of a .1M solution of acetic acid is 2.8.

Acids and bases react to form salt and water.
HCl + NaOH ===> NaCl and H₂O.

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Koni Stone
Koni@chem.csustan.edu