Acids Bases

Acids Acids were first recognized as a distinct class of compounds because of the common properties of their aqueous solutions. Aqueous solutions have a sour taste (many are corrosive and poisons). Acids change the color of acid-base indicators. Some acids react with active metals to release hydrogen gas, H2.

Common Industrial Acids Acids react with bases to produce salts and water. Some acids conduct an electric current. Common Industrial Acids Sulfuric Acid Used in petroleum refining, automobile batteries, and used as a water-removing agent (can cause serious burns).

Common Industrial Acids Nitric Acid Used in making explosives (stains skin and causes serious burns). Phosphoric Acid Used for manufacturing fertilizers and animal feed and for flavoring beverages.

Common Industrial Acids Hydrochloric Acid Used in food processing. Acetic Acid Used in the manufacture of plastics and as a fungicide.

Bases Aqueous solutions of bases have a bitter taste. 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.

Acid-Base Theories Arrhenius Acid An Arrhenius acid is a chemical compound that increases the concentration of hydrogen ions, H+, in aqueous solution. Examples: HCl, H2SO4, HI, HF

Arrhenius Base An Arrhenius base is a substance that increases the concentration of hydroxide, OH-, in aqueous solution. Examples: NaOH, LiOH, Ca(OH)2

Bronsted-Lowry Acids and Bases Acid-Base Theories Bronsted-Lowry Acids and Bases A Brønsted-Lowry acid is a molecule or ion that is a proton donor (H+). A Brønsted-Lowry base is a molecule or ion, that is a proton acceptor. In a Brønsted-Lowry acid-base reaction, protons are transferred from one reactant (the acid) to another (the base). HCO3 + HOH → H2CO3 + OH- Base Acid

Acid-Base Theories Lewis Acids and Bases A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond. A Lewis base is an atom, ion, or molecule that donates an electron pair to form a covalent bond. A Lewis acid-base reaction is the formation of one or more covalent bonds between an electron-pair donor and an electron-pair acceptor.

Concepts of pH

Hydronium and Hydroxide Ions Pure water is a weak electrolyte and undergoes self-ionization as seen below. Remember ionization is the process of adding or removing electrons from an atom or molecule, which gives the atom or molecule a net charge. In the self-ionization of water, two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. hydronium ion hydroxide ion (Acid) (Base)

Concentrations of hydronium ion (H3O+) and hydroxide ion (OH-) are 1.0 x 10-7 mol/L in water at 25 oC. The product of [H3O+][OH-] = 1.0 x 10-14 and the product is called the ionization constant of water, Kw. Note: [ ] means molar concentration (mol/L).

Neutral, Acidic, and Basic Solutions Any solution in which [H3O+] = [OH-] is neutral. Any solution in which [H3O+] is greater than [OH-] is acidic. Remember acids increase the concentration of H3O+ in aqueous solutions. Any solution in which [OH-] is greater than [H3O+] is basic. Remember bases increase the concentration of OH- in aqueous solutions.

pH Instead of expressing acidity or basicity in terms of the concentration of H3O+ or OH-, a quantity called pH is used.

pH Scale The pH scale commonly has values from 0 to 14 with a pH value of 7 considered neutral. pH values less than 7 are acidic and pH value greater than 7 are basic.

Calculating pH pH indicates the hydronium ion (H3O+) concentration of a solution. The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration. pH = -log[H3O+] or pH = [H+] pOH (hydroxide ion concentration) pOH = -log[OH-] pH + pOH = 14.0

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