Properties of Acid and Bases
Acids and bases have characteristics different from most other materials. The following table gives properties and examples of each:
Property
Taste Touch Reactivity with metals Conducts electricity? pH Reaction with phenolphthalien indicator Reaction with universal indicator Examples |
Acid
Tart Will sting, especially on a cut Vigorously and produces bubbles Yes 0 to below 7 Colorless Red, orange, yellow Fruits, soft drinks, coffee, milk |
Base
Bitter Feels slippery, because it is dissolving skin No reaction Yes above 7 to 14 Pinkish-purple Blue, violet Blood, eggs, soap, ammonia, drain cleaner |
Definitions of Acids and Bases
There are two definitions for the classification of acids and bases. The first is called the Arrhenius Definition (1884). Arrhenius said that acids and bases release specific ions in water:
There are two definitions for the classification of acids and bases. The first is called the Arrhenius Definition (1884). Arrhenius said that acids and bases release specific ions in water:
Acids - dissociate to produce H+ ions in water
Bases - dissociate to produce OH- (hydroxide) ions in water
Or in simpler terms, a substance that begins with H+ will be an acid. like HCl (stomach acid) and H2SO4 (battery acid). A substance that ends with an OH- will be a base, like NaOH and Ca(OH)2 (drain cleaners).
Bases - dissociate to produce OH- (hydroxide) ions in water
Or in simpler terms, a substance that begins with H+ will be an acid. like HCl (stomach acid) and H2SO4 (battery acid). A substance that ends with an OH- will be a base, like NaOH and Ca(OH)2 (drain cleaners).
pH
The pH scale, designed by Sorensen, was a proposal that expresses acidity and basicity in a more compact form. Using the molarities of H+ and OH- to determine whether a solution is acidic or basic is confusing. The pH scale is designed to make the numbers easier to work with. Since the molar concentration of hydronium is different in different substances, we use a scale to show this concentration.
The pH scale appears at right: To determine the pH from the hydronium concentration, we use the following formula: pH = -log [H+]
On the pH scale, acids range from 0 to just below 7. 7 is neutral and from just above 7 to 14 is the bases. The farther you get from 7, the more acidic or basic the solution is. Example 2: What is the pH of the orange juice solution in example #1? Answer: Since the H+ is equal to 6.7 x 10-5 M, then
pH = -log [6.7 x 10-5]
pH = 4.18 A pH of 4.18 is in the acid range of the pH scale.
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