Chapter 15

Acids and Bases

Sect. 15-1: Properties of Acids and Bases

AcidsHave a sour tasteChange the color of acid-base indicatorsSome react with metals to produce hydrogen

gas (if above hydrogen on activity series)React with bases to produce a salt and waterSome conduct electric current

Acid nomenclature Binary acid – contains hydrogen and one other

element (hydro- root –ic acid) Oxyacid – contains hydrogen, oxygen, and one other

element (-ate polyatomic ions become –ic acids and –ite polyatomic ions become –ous acids)

Common industrial acids Sulfuric acid – petroleum refining, metallurgy, fertilizer Nitric acid – explosives, plastics, pharmaceuticals, etc Phosphoric acid – fertilizer, animal feed, soft drinks Hydrochloric acid – metal work, cleaning masonry Acetic acid – used in chemical synthesis

BasesTaste bitterChange the color of acid-base indicatorsFeel slipperyReact with acids to produce a salt and waterConduct electric current

Arrhenius acid – a chemical compound that increases the concentration of hydrogen ions in aqueous solution

Arrhenius base – a substance that increases the concentration of hydroxide ions in aqueous solution

Aqueous solutions of acidsAcid molecules attract water molecules which

take the hydrogen (forming hydronium, H3O+) and leave behind an anion

HNO3 + H2O H3O+ + NO3-

Aqueous solutions of bases Ionic compound will dissociate to produce

cations and hydroxide ions NaOH Na+ + OH-

Alkaline – a solution that is created when a base completely dissociates in water to yield aqueous hydroxide ions

Other bases produce hydroxide ions by reacting with water molecules

NH3 + H2O NH4+ + OH-

Strength of acids and bases

Strong acid – ionizes completely in aqueous solutions; strong electrolyte

Weak acid – acids that are weak electrolytes

Strong bases – strong electrolytes Weak bases – produces a relatively low

concentration of hydroxide ions in solution

Strong acids Chloric acid Hydrobromic acid Hydrochloric acid Hydroiodic acid Nitric acid Perchloric acid Sulfuric acid

Sect. 15-2: Acid-Base Theories

Arrhenius definition of acid/base requires aqueous solutions, but substances act as acid/base at other times as well, so other definitions had to be created (Brønsted-Lowry and Lewis)

Brønsted-Lowry acid – a molecule or ion that is a proton donor (remember, H+ is a proton)

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

HCl + NH3 NH4+ + Cl-

HCl is acting as an acid and NH3 as a base by B-L definition

Brønsted-Lowry acid-base reaction – protons are transferred from one reactant (the acid) to another (the base)

Monoprotic acid – an acid that can donate only one proton per molecule (ex. HCl)

Polyprotic acid – an acid that can donate more than one proton per molecule (ex. H2SO4)Hydrogen atoms are lost one at a timeDiprotic acid – can donate 2 protons per

moleculeTriprotic acid – can donate 3 protons per

molecule

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

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

Lewis acid-base reaction – the formation of one or more covalent bonds between an electron-pair donor and an electron-pair acceptor

Sect. 15-3: Acid-Base Reactions

Conjugate base – the species that remains after a Brønsted-Lowry acid has given up a protonHF + H2O F- + H3O+

Since HF is the acid, F- is the conjugate base

Conjugate acid – the species that is formed when a Brønsted-Lowry base gains a protonHF + H2O F- + H3O+

Since water is acting as a base, the H3O+ is the conjugate acid

The base and its conjugate acid are referred to as a conjugate acid-base pair

Strength of conjugate acid/base

Strong acids produce weak conjugate bases The stronger a base, the weaker its conjugate

acid will be Pg. 471 Proton transfer reactions favor the production of

the weaker acid and weaker base

Amphoteric – any species that can react as either an acid or a baseWater acts as base with HCl, but was acid

with NH3

Molecular compounds containing the hydroxyl group (-OH) can either be amphoteric or acidic

The more oxygen atoms attached to the atom to which the –OH group is attached, the more acidic it will be due to polarity of the bonds

Neutralization reactions

Neutralization – reaction of hydronium ions and hydroxide ions to form water molecules

Salt – an ionic compound composed of a cation from a base and an anion from an acid

Acid rain is caused by gases (NO, NO2, SO2, SO3) from industrial processes reacting with water vapor in the air to form acids such as sulfuric and nitric acid

Acid rain reacts with marble in statues and buildings, eroding it away