Ch # 6 Acids, Bases and Salts

ACIDS An acid “is a hydrogen-containing substance that produces hydrogen ions” in water. (Hydronium ion: H3O+) An aqueous solution that contains more H+ ions than OH- ions is ‘acidic’

ACID PROPERTIES Sour taste (think lemons and sour candies) Change the color of litmus from blue to red.

Acid Properties (cont.) React with a base to produce water and salt in a double displacement neutralization reaction. React with metals such as zinc and magnesium to produce hydrogen gas in a single replacement reaction.

BASES An base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution. An aqueous solution that contains more OH- ions than H+ ions is ‘basic’

BASE PROPERTIES Bitter or caustic taste. A slippery, soapy feeling. The ability to change litmus red to blue. The ability to interact with acids in a neutralization reaction to produce water and salt.

Ionization/Dissociation. Ionization: A process in which ions are produced from a molecular compound when dissolved in a solvent. ACIDS Dissociation: A process in which already existing ions in an ionic compound separate when an ionic compound is dissolved in a solvent. BASES

Amphoteric substances Glycine Hydrogen carbonate

Other kinds of acids and bases FeCl3 A metal ion that is acidic CO32- An anion that is basic NH4+ A cation that is acidic

Salts A salt is an ionic compound containing a metal cation and a nonmetal anion Produced in a neutralization reaction: HCl + NaOH  H2O + NaCl

6.3 Conductance of A, B, S Solutions Strong electrolyte Weak electrolyte Non-electrolyte

Strong acids & bases – strong electrolyte 6.4 Dissociation of A & B Strong acids & bases – strong electrolyte Weak acids & bases – weak electrolyte

6.5 Buffers A solution that resists major changes in pH when small amounts of acid or base is added to it. 1) A substance to react with and remove added base. 2) A substance to react with and remove added acid. 3) weak acid-salt.

6.6 pH and Acidic / Basic Solutions

Self ionization of water: Ion product constant for water: Kw = [H3O+] [OH-] = 1.00 x 10-14 If [H3O+] = 7.50 x 10-5 M What is the [OH-] in this solution?

pH = -log [H3O+] = -log [H+]

H3O+

Acidic solution: [H3O+]> [OH-] pH= 0-6 Basic solution: [H3O+]< [OH-] pH =8-14 Neutral solution: [H3O+]= [OH-] pH =7 pH scale: Scale that is used to specify molar hydronium ion concentration in an aqueous solution.

Problems Calculate pH for the following and identify as acidic or basic: [H3O+] = 1 X 10-3 [H3O+] = 1 X 10-9 [OH-] = 1 X 10-4 [H3O+] = 3.9 X 10-5 [H3O+] = 7.9 X 10-11 The number of decimal places of a logarithm is equal to the number of significant figures in the original number.

Problem The pH of a solution is 5.70. What is the molar hydronium ion concentration for this solution? [H3O+] = 10-pH

6.7 Preparation of Acids H2(g) + Cl2(g)  2HCl(g) 2NaCl + H2SO4  2HCl(g) + Na2SO4 SO2(g) + H2O  H2SO3

6.8 Preparation of bases: Alkali metal and water to produce hydrogen and a hydroxide salt. Ammonia in water Carbonate in water

6.9 Preparation of Salts The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water. Solvay process for making NaHCO3 and Na2CO3 (p226)

Reactions of salts: Reaction with metals: Single replacement reaction according to activity series. Reaction with acids: Double displacement reaction. A new weaker acid, new insoluble salt, gaseous compound is one of the products. Reaction with bases: Insoluble precipitate forms, or weaker base. Reaction of salts with each other: Double displacement reaction. Insoluble salt is formed.

6.10 Acidic and Basic Salts Ions that contain H+ Bases: See Page 213 Hydroxyapatite Ca5OH(PO4)3 Reactions: NaHCO3 + NaOH  Na2CO3 + H2O

6.11 Water of Hydration Water binds to some salts: These are hydrates. They are used as desiccants (drying agents). A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its vicinity. Anhydrous (without water of hydration)

Examples and names CaSO4▪2H2O calcium sulfate dihydrate (gypsum-dry wall, plaster of paris, Dri-rite) CuSO4▪5H2O copper(II) sulfate pentahydrate