Chapter 10 Acids (酸) and Bases （碱）

10.1 Acids donate protons, bases accept them Sulfuric acid is the number one manufactured chemical, 85 billion pounds (40,000,000 tons) annually in US. Acid has “sour” taste. Bases have “bitter” taste and slippery feel. In US, 25 billion pounds (10,000,000 tons) of NaOH was manufactured. Examples of acides

By definition, acids are chemicals that donate hydrogen ions, and bases are chemicals that accept them. HCl + H2O Cl- +H3O+ (hydronium ion) H+ donor H+ acceptor (acid) (base) H2O + NH3 OH- + NH4+ H+ donor H+ acceptor H+ acceptorH+ donor (acid) (base) (base) (acid)

A salt is the product of an acid-base reaction (neutralization 中和) Acid Base Salt Water HCN + NaOH NaCN + H2O Hydrogen Sodium Sodium Cyanide Hydroxide Cyanide HNO3 + KOH KNO3 + H2O Nitric Potassium Potassium acid Hydroxide nitrate 2HCl + Ca(OH)2 CaCl2 + 2H2O Hydrogen Calcium Calcium Chloride Hydroxide chloride HF + NaOH NaF + H2O Hydrogen Sodium Sodium fluoride Hydroxide fluoride Table10.1 acid-base reactions and the salts formed

10.2 Some acids and bases are stronger than others The stronger an acid, the more readily it donates hydrogen ions. The stronger a base, the more readily it accepts hydrogen ions.

A nonelectrolyte B strong electrolyte C weak electrolyte The pure water in this circuit is unable to conduct electricity because it contains practically no ions Because HCl is a strong acid, nearly all of its molecules break apart in water, giving a high concentration of ions Acetic acid, C2H4O2, is a weak acid and in water only a small portion of its molecules break up into ions

10.3 Solutions can be acidic, basic or neutral In water, equal amount of H3O+ and OH- (10-7M) (neutral solution) In acidic solution, more H3O+ than OH- In basic solution, more OH- than H3O+

Acidity 酸性 (and basicity 碱性) can be scaled by pH value pH = -log[H3O+]

10.4 Rainwater is acidic and ocean water is basic The main sources of acidic rainwater are CO2 and SO2. The damage of acidic rainwater depends on the local geology. 1. rain is acidified as it falls through the air 2. acid enters lake from rain 3. hydronium ions are neutralized by calcium carbonate released from limestone 2H3O++CaCO3 3H2O+CO2+Ca2+ 1.Rain is acidified as it falls through the air 2. acid enters lake from rain 3. hydronium ions concentration increases, with potential harm to the ecosystem

Carbon dioxide is absorbed and released Ocean can absorb CO2 Carbon dioxide is absorbed Carbon dioxide is absorbed and released Ocean PH=8.2 Fresh-water lake PH<7

The concentration of CO2 in air has been increased, which is related to global warming Fig10.18 Researchers at the Mauna Loa Weather Observatory in Hawaii have recorded increasing concentrations of atmospheric carbon dioxide since they began to collecting data in the 1950s.The chart left shows how the concentration of CO2 in the atmosphere has changed in the last 40 years

10.5 Buffer solutions (缓冲溶液) resist changes in pH Effective buffer solutions can be prepared by mixing a weak acid with a salt of the weak acid. Fig10.19 Hydrochloric acid added to a solution containing acetic acid and sodium acetate is neutralized by the sodium acetate to form Additional acetic acid Fig 10.20 Sodium hydroxide added to a Solution containing acetic acid and sodium Acetate is neutralized by the acetic acid To form additional sodium acetate