Acids produce H+ ions. Bases produce OH- ions. When something is neutral, it has equal amounts of H+ and OH-. Usually, acids and bases are dissolved in water; water provides both H+ and OH- ions. Sometimes you will see H3O+ (hydronium ion) instead of H+ (hydrogen ion). DEFINING ACIDS AND BASES
Acids and bases can be understood in terms of the ions they release when they dissolve in water. An acid is a substance that dissociates in water to produce hydrogen ions (H+). A base is a substance that dissociates in water to produce hydroxide ions (OH-). HCl + NaOH NaCl + H2O H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O (HOH)
DEFINING ACIDS AND BASES The pH scale is the measure of hydrogen ion concentration and acidity. It measures from 0 to 14. pH of an acid = 0 up to but not including 7 pH of a base = 14 down to but not including 7 pH of neutral = 7
pH SCALE pH SCALE The smaller the pH, the more acidic the solution. Three methods to measure pH: Litmus paper, indicators - usually measure a range and are not as accurate.
pH paper measures within a number or two and more accurate than litmus. pH meter electronically measures pH pH SCALE A. Taste Acids taste sour or tart. Bases taste bitter. ACIDS AND BASES PROPERTIES
B. Touch Dilute acids feel like water. Stronger acids are corrosive. Mild bases feel smooth and slippery. Strong bases are corrosive. ACIDS AND BASES PROPERTIES C. Reaction with metals
Acids react vigorously with metals, sometimes producing a gas. Mg + HCl MgCl2 + H2 (g) ACIDS AND BASES PROPERTIES D. Reaction with Carbonates/Hydrogen Carbonates Acids react vigorously with carbonates or hydrogen
carbonates, producing a gas. NaHCO3 + HC2H3O2 NaC2H3O2 + H2O + CO2 ACIDS AND BASES PROPERTIES E. Electrical conductivity Pure water is an extremely poor
conductor of electricity. An aqueous solution of a strong acid or base conducts electricity well. Acids and bases are examples of electrolytes. Electrolytes ionize when they dissolve in water. A solution containing electrolytes conducts electricity. ACIDS AND BASES
PROPERTIES F. Indicators An acid-base indicator is a substance that turns one color in an acidic solution and another color in a basic solution. Examples: Litmus - acid is red and base is blue Phenolphthalein acid is colorless or white, base is pink
ACIDS AND BASES PROPERTIES INDICATORS G. pH Acids: pH 0 7 Examples: Stomach acid pH 2
(known as hydrochloric acid) Vinegar pH 3 (known as acetic acid) Soft Drink pH 4 (known as carbonic acid) Bases: pH 7-14
Examples: Baking Soda pH 9 Ammonia pH 11 Bleach pH 13 ACIDS AND BASES PROPERTIES
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