Acids and Bases Chapter 19

Common Acids and Bases  Acids originally recognized as sour taste. EX: Vinegar (acetic acid) and Lemons (citric acid)  Bases bitter taste and soapy feel. Most hand soaps and drain cleaners.

Definition of Acids and Bases  Many models  Arrhenius Model: first model recognized.  Acids: produce hydrogen ions (H + ) in aqueous solution.  Bases: produce hydroxide ions (OH - ) in aqueous solution.

Arrhenius Acids and Bases  Acids in solution. HCl (aq) → H + (aq) + Cl - (aq)  Acids dissociate, separate into ions, in aqueous solution  Bases in solution NaOH (s) → Na + (aq) + OH - (aq)  Bases dissociate in aqueous solution.

Naming Acids I.All acids begin with hydrogen II.If no oxygen in anion, prefix hydro- add suffix –ic and word acid. EX: HCl = hydrochloric acid. III.When anion is a polyatomic ion ending in –ate, change to –ic and add word acid. EX: HNO 3 = nitric acid IV.When anion is a polyatomic ion ending in –ite, change to –ous and add word acid EX: HNO 2 = nitrous acid

pH Scale  Ranges from 0 to 14  0 is strongly acidic.  14 is strongly basic.  7 is neutral.  pH = -log [H + ]  Exponential scale pH 7 has ten times more H + than pH 6

Neutralization Reaction  Acid + Base → Salt + Water  HCl + NaOH → NaCl + H 2 0  Always products when dealing with acids and bases.  Predict Products for the following reactions HNO 3 + NaOH → HBr + NaOH →

Neutralization Reaction  Reaction is overall exothermic  HCl + NaOH → NaCl + H 2 0 Endothermic < Exothermic  Breaking bonds of acids and bases, endothermic, but combining of NaCl and H 2 0 more exothermic.

Enthalpy  Enthalpy: heat content of a system at constant pressure. H is variable for enthalpy  ΔH change in enthalpy  If ΔH is negative, exothermic  If ΔH is positive, endothermic

Buffers  Solutions that resist changes in pH when limited amounts of acid or base are added.  A buffer is a weak acid and its product.

Buffers  Biological systems need very specific pH  Blood pH 7.4, stomach acid pH Solutions are buffered.  Acidosis can occur if blood pH drops 0.3 units

Acid Rain  SO 3 + H 2 O → H 2 SO 4  Gasses react with atmospheric water to form acids, forms acid rain.  SO 3, SO 2, CO 2, NO 2 all form acid rain.  Increases acidity of soil and water hurts wildlife.  pH of rain has been recorded as 1.8