Properties and Theories of Acids and Bases

Section 14.1 and 14.2

Acids

• Aqueous solutions of acids have a sour taste (never taste chemicals)

• Will change the color of acid-base indicators• Some acids react with active metals and

release hydrogen gas• React with bases to produce salts and water• Acids conduct electric current (varies)

Acids turn blue litmus paper red

Naming Acids

• Binary acid: contains only two different elements; hydrogen and one other more electronegative element– The name of a binary acid begins with the

prefix hydro-– The root of the name of the second

element follows this prefix– The name then ends with the suffix -ic

Examples of Naming

Naming Oxyacids

• Oxyacid: an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal

Common Industrial Acids

• Sulfuric acid: the most commonly produced industrial chemical in the world– H2SO4

– Used for making: fertilizer, paint, paper, detergents, dyes, batteries for cars, also used in refining

• Nitric acid– HNO3

– Used for making explosives, rubber, plastics, dyes, pharmaceuticals

More Acids• Phosphoric acid– H3PO4

– Most is used directly for manufacturing fertilizers and animal feed, used as a flavoring agent in beverages

• Acetic acid– CH3COOH

– Vinegars, synthesizing chemicals used in making plastics, raw material in production of food supplements

One More Acid

• Hydrochloric acid– HCl– Used to remove surface impurities from metals, as

a cleaning agent, food processing, activation of oil wells, recovery of magnesium from sea water, making other chemicals

– Concentrated HCl is commonly called muriatic acid and can be found in hardware stores

Bases

• Aqueous solutions of bases taste bitter (never taste chemicals)

• Bases change the color of acid-base indicators• Dilute aqueous solutions of bases feel slippery• Bases react with acids to produce salts and

water• Bases conduct electric current (varies)

Bases turn red litmus paper blue

Common Bases

• Ammonia– NH3

– http://www.rmtech.net/uses_of_ammonia.htm

• NaOH (sodium hydroxide)– http://www.chemicalland21.com/industrialchem/i

norganic/CAUSTIC SODA.htm

Another Base

• Baking soda– NaHCO3

– food & food processing, beverages , pharmaceuticals , animal foodstuffs , household cleaning products , rubber & plastics foam blowing , fire extinguishers & explosion suppression , effluent & water treatment, flue gas treatment , oil drilling , industrial & chemical processes

Svante Arrhenius

• Svante Arrhenius was a Swedish chemist who lived from 1859-1927

• He realized that aqueous solutions of acids and bases conducted electricity

• He then theorized that they produce ions in solution

Arrhenius Acid and Base Theory

• Arrhenius acid: a chemical compound that increases the concentration of hydrogen ions, H+, in aqueous solution

• Arrhenius base: a substance that increases the concentration of hydroxide ions, OH-, in aqueous solution

Aqueous Solutions of Acids

• Acid molecules are polar, so the water molecules attract one or more of the hydrogen ions when the acid dissociates in water

• HNO3(aq) + H2O(l) H3O+(aq) + NO3

-(aq)

Strength of Acids

• Strong acid: one that dissociates completely in aqueous solutions

• Concentration is not linked to strength• Weak acid: one that releases few

hydrogen ions in aqueous solution• When a weak acid is dissolved in water,

the reverse reaction occurs simultaneously

Weak Acid Solution

• HCN(aq) + H2O(l) H3O+(aq) + CN-

(aq)

• The number of the hydrogen atoms in the formula does not indicate acid strength

• Organic acids, that contain COOH are usually weak acids

Aqueous Solutions of Bases

• Most bases are ionic compounds containing a metal cation and the hydroxide anion, so they dissociate in water

Strength of Bases

• Strong base: one that completely dissociates in solution

• Strong bases are also strong electrolytes (as well as strong acids)

• Electrolyte: a substance that dissolves in water to give a solution that conducts an electric current

Strength of Bases

• Bases that are not very soluble do not produce a large number of hydroxide ions when added to water

• They are weak bases• Some bases, like NH3, are soluble, but do

not form many OH- ions, so they are weak

Another Theory

• Chemists noticed that some substances acted like acids and bases, but were not in a water solution

• The Arrhenius theory required an aqueous solution

• Another theory had to be considered

Brønsted-Lowry Theory

• Named for 2 chemists J. N. Brønsted and T. M. Lowry who independently expanded the Arrhenius theory

• Brønsted-Lowry acid: a molecule or ion that is a proton donor (H+ is a proton)

• Brønsted-Lowry base: a molecule or ion that is a proton acceptor

Brønsted-Lowry Acid

• Any Arrhenius acid also qualifies as a Brønsted-Lowry acid, but not vice-versa

• HCl + NH3 NH4+ + Cl-

• A proton is donated by the hydrogen chloride molecule even though it is not aqueous

• Water can also act as a Brønsted-Lowry acid

Monoprotic and Polyprotic Acids• Monoprotic acid: an acid that can donate only

one proton (hydrogen ion) per molecule• Examples: HCl and HNO3

• Polyprotic acid: an acid that can donate more than one proton per molecule

• Examples: H2SO4 and H3PO4

• Diprotic acid: an acid that donates two protons per molecule

Another Theory

• Some species behave like acids and bases even though they do not contain, or react to form, a hydrogen ion

• G. N. Lewis, of Lewis stucture fame, proposed a new theory

Lewis Theory of Acids and Bases

• Lewis acid: an atom, ion, or molecule that accepts an electron pair to form a coordinate covalent bond

• Lewis base: an atom, ion, or molecule that donates an electron pair to form a coordinate covalent bond

• An example of a Lewis acid-base reaction is the reaction between boron trifluoride and ammonia

Summary of Theories