Solutions, Acids, and Just the Bases Mrs. Herrmann

Solutions Soluble—capable of being dissolved. Soluble—capable of being dissolved. Solution—a homogeneous mixture of two or more substances in a single phase. Solution—a homogeneous mixture of two or more substances in a single phase. Solvent—the stuff doing the dissolving Solvent—the stuff doing the dissolving Solute—the stuff being dissolved Solute—the stuff being dissolved Homogeneous Mixture—Solution Homogeneous Mixture—Solution Heterogeneous Mixture—Suspension Heterogeneous Mixture—Suspension --Colloids (Tyndall) --Colloids (Tyndall)

Solutions--continued Electrolyte—a substance that dissolves in water to give a solution that conducts electric current. Electrolyte—a substance that dissolves in water to give a solution that conducts electric current. Nonelectrolyte—a substance that dissolves in water to give a solution that does not conduct an electric current. Nonelectrolyte—a substance that dissolves in water to give a solution that does not conduct an electric current.

Factors Affecting Dissolution 1. Surface Area—increase to increase rate of dissolving 2. Agitation—stirring or shaking to increase rate of dissolving (not for gases in liquid!—think carbonated drink 3. Heating—increase temperature (again not for gases in liquid) increases rate of dissolving.

Solubility  Solution equilibrium—physical state in which rate of dissolution equals the rate of crystallization.  Solubility—generally described in terms of grams solute per 100grams of solvent at a specified temperature  Unsaturated solution—solution contains less than the maximum amount of solute that can be dissolved in the solvent at described conditions.

Solubility continued  Saturated solution—solution contains the maximum amount of solute that can be dissolved in the solvent at described conditions  Supersaturated solution—solution contains more than the maximum amount of solute capable of being dissolved in the solvent at described conditions  Solution generally has to be heated and then cooled to the described conditions  Unstable

Concentrations of Solutions Concentration—quantitive; a measure of the amount of solute in a given amount of solvent or solution. Molarity (M)—number of moles solute per liter of solution M = moles of solute liters of solution liters of solution Molality (m)—number of moles solute per kilogram of solvent m = moles of solute__ m = moles of solute__ kilograms of solvent kilograms of solvent

Aqueous Solutions Two Confusing and Subtle Definitions Dissociation: The separation of ions that occurs when an ionic compound dissolves. (Ions that are already present separate from one another.) Dissociation: The separation of ions that occurs when an ionic compound dissolves. (Ions that are already present separate from one another.) H 2 O H 2 O Example: NaCl(s)  Na + (aq) + Cl - (aq) Example: NaCl(s)  Na + (aq) + Cl - (aq) Ionization: The process by which ions are formed from solute molecules (polar) by the action of the solvent. (Ions form where none were present.) Ionization: The process by which ions are formed from solute molecules (polar) by the action of the solvent. (Ions form where none were present.) H 2 O H 2 O Example: HCL  H + (aq) + Cl - (aq) Example: HCL  H + (aq) + Cl - (aq)

Two Easy Definitions Electrolyte : Substances that dissolve in water to form ions Electrolyte : Substances that dissolve in water to form ions Strong electrolyte—almost ALL the dissolved compound exists as ions in aqueous solution Weak electrolyte—relatively small amount of the dissolved compound exists as ions in aqueous solution Note: degree of ionization or dissociation indicates whether an electrolyte is strong or weak NOT the concentration of the solution! Nonelectrolyte : substances that dissolve in water but do not form any ions Nonelectrolyte : substances that dissolve in water but do not form any ions

Colligative Properties of Solutions Colligative Properties: properties that depend on the concentration of solute particles but not on their identities. Boiling point of a pure solvent is increased with the addition of a nonvolatile solute Freezing point of a pure solvent is decreased with the addition of a nonvolatile solute

More on Colligative Properties WHY? The vapor pressure is the pressure caused by molecules that have escaped from the liquid to the gaseous phase. Or more simply, vapor pressure is the measusre of the tendency of molecules to escape the liquid. WHY? The vapor pressure is the pressure caused by molecules that have escaped from the liquid to the gaseous phase. Or more simply, vapor pressure is the measusre of the tendency of molecules to escape the liquid. Addition of a solute lowers the concentration of exposed solvent molecules at the surface, so fewer solvent molecules are allowed to escape to the vapor phase. Addition of a solute lowers the concentration of exposed solvent molecules at the surface, so fewer solvent molecules are allowed to escape to the vapor phase. The concentration of nonelectrolyte solutions equals the concentration of the particles of solute. The concentration of nonelectrolyte solutions equals the concentration of the particles of solute. The concentration of electrolyte solutions depends on the number of particles (ions) formed by the ionization or dissociation of the solute. The concentration of electrolyte solutions depends on the number of particles (ions) formed by the ionization or dissociation of the solute.

Formulas used with Colligative Properties Freezing point depression ΔT f = moles of solute k f (# particles solute breaks into) kg of solvent Boiling point elevation ΔT b = moles of solute k b (# particles solute breaks into) ΔT b = moles of solute k b (# particles solute breaks into) kg of solvent kg of solvent ****NOTE: these equations do NOT solve for the freezing point or the boiling point. It only tells you by how much the freezing point is lowered or by how much the boiling point is raised.

Boiling point and Freezing point What is the boiling point of a solution in which 75 grams of sodium sulfate are dissolved in 800. grams of water? What is the boiling point of a solution in which 75 grams of sodium sulfate are dissolved in 800. grams of water? What is the freezing point of a solution in which 100. grams of sugar, C 12 H 22 O 11, is dissolved in 750 grams of water? What is the freezing point of a solution in which 100. grams of sugar, C 12 H 22 O 11, is dissolved in 750 grams of water? What is the freezing point of a solution in which 100. grams of salt, NaCl, is dissolved in 750 grams of water? What is the freezing point of a solution in which 100. grams of salt, NaCl, is dissolved in 750 grams of water?

The Hydronium Ion H + ion attracts other molecules or ions so strongly that it normally does not exist alone. Ionization of monoprotic or polyprotic acid in water best described as a transfer of a proton from the acid to a water molecule to form the Hydronium ion. H 3 O + Highly exothermic which generally provides enough energy to ionize a molecular solute Example: H 2 O(l) + HCl(g)  H 3 O + (aq) + Cl - (aq)

Acids and Bases Properties Acids Bases Acids Bases Sour taste Bitter taste Sour taste Bitter taste Change the color of acid- Change the color of acid- Change the color of acid- Change the color of acid- base indicators base indicators base indicators base indicators Blue litmus turns red Red litmus turns blue Blue litmus turns red Red litmus turns blue React with active metals Dilute aqueous solutions React with active metals Dilute aqueous solutions to release hydrogen gas feel slippery to release hydrogen gas feel slippery React with bases to form React with acids to form React with bases to form React with acids to form salts and water salts and water salts and water salts and water Some conduct electric Conduct electric current Some conduct electric Conduct electric current current current

Arrhenius Acids and Bases 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.

Brønsted-Lowry Acids and Bases Brønsted-Lowry Acid—is a molecule or ion that is a proton donor. Brønsted-Lowry Acid—is a molecule or ion that is a proton donor. Brønsted-Lowry Base—is a molecule or ion that is a proton acceptor. Brønsted-Lowry Base—is a molecule or ion that is a proton acceptor. Example: HCl + NH 3  NH Cl - Example: HCl + NH 3  NH Cl - where HCl is the Brønsted-Lowry Acid and where HCl is the Brønsted-Lowry Acid and NH 3 is the Brønsted-Lowry Base NH 3 is the Brønsted-Lowry Base

Conjugate Acids and Bases Conjugate Acid—is the species that is formed when a Brønsted-Lowry base gains a proton. Conjugate Acid—is the species that is formed when a Brønsted-Lowry base gains a proton. Conjugate Base—is the species that that remains after a Brønsted-Lowry acid has given up a proton. Conjugate Base—is the species that that remains after a Brønsted-Lowry acid has given up a proton. HF(aq) + H 2 0(l)  F - (aq) + H 3 O + (aq) HF(aq) + H 2 0(l)  F - (aq) + H 3 O + (aq) acid base conjugate base conjugate acid acid base conjugate base conjugate acid

Lewis Acids and Bases Lewis Acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond. Lewis Base is an atom, ion, or molecule that donates an electron pair to form a covalent bond. (an anion) Example: BF3(aq) + F-(aq) BF4-(aq) Where BF3 is the Lewis Acid and F- i is the Lewis Base

Ionization of Water In the self-ionization of water: In the self-ionization of water: H 2 O(l) + H 2 O(l)  H 3 O + (aq) + OH - (aq) H 2 O(l) + H 2 O(l)  H 3 O + (aq) + OH - (aq) at constant temperature the concentrations of hydronium ion and hydroxide ions remain constant in water and dilute aqueous solutions, so that the ionization constant of water is: K w = [H 3 O + ][OH - ] K w = [H 3 O + ][OH - ] K w = (1.0 x ) (1.0 x ) K w = (1.0 x ) (1.0 x ) K w = 1.0 x K w = 1.0 x

pH and [H 3 O + ] pH—French word “pouvoir hydrogène” which means “hydrogen power” pH—French word “pouvoir hydrogène” which means “hydrogen power” pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration pH = -log[H 3 O + ] pH = -log[H 3 O + ] [H 3 O + ] ranges from 1 to so [H 3 O + ] ranges from 1 to so pH ranges from 0 to 14 pH ranges from 0 to 14

pOH and [OH - ]  pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration, [OH - ]  pOH = -log[OH - ]  [OH - ] ranges from 1 to so  pOH ranges from 0 to 14

pH and pOH Ranges So for a neutral solution of water K w = [H 3 O + ][OH - ] K w = [H 3 O + ][OH - ] 1.0 x = (1.0 x ) (1.0 x ) so -log K w = -log[H 3 O + ] + -log[OH - ] so -log K w = -log[H 3 O + ] + -log[OH - ] pK w = pH + pOH pK w = pH + pOH 14 = = But if the [H 3 O + ] > [OH - ] then pH < pOH pH < pOH and pH 7 and is defined as acidic and pH 7 and is defined as acidic if the [H 3 O + ] < [OH - ] then if the [H 3 O + ] < [OH - ] then pH > pOH pH > pOH and pH > 7 and pOH 7 and pOH < 7 and is defined as basic

Calculating [H 3 O + ] and [OH - ] from pH Remember pH = -log [H3O+] so log [H3O+] = -pH [H3O+] = antilog(-pH) [H3O+] = 10-pH

That’s all !