SOLUTIONS. Definitions. Other types of solutions. Types of solutions: solid-liquid. Gas-gas Example: Air

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1 SOLUTIONS Definitions A solution is a system in which one or more substances are homogeneously mixed or dissolved in another substance homogeneous mixture -- uniform appearance -- similar properties throughout mixture The solvent is the dissolving agent -- i.e., the most abundant component of the solution The solute is the component that is dissolved -- i.e., the least abundant component of the solution Types of solutions: solid-liquid Solute: Potassium permanganate (KMnO 4 ) Gas-gas Example: Air Other types of solutions Solvent: Nitrogen gas (N 2 ) Solutes: O 2, Ar, CO 2, water vapor, etc. Solvent: Water solution (solid-liquid) Gas-liquid Example: Carbonated drinks (soda, sparkling water, etc.) Solvent: Water Solute: CO 2

2 Other types of solutions Other types of solutions Liquid-liquid Example: Antifreeze Solvent: Water Solute: Ethylene glycol Gas-solid H 2 Solid-solid Example: Brass Solvent: Copper Solute: Zinc Example: H 2 / Pt catalyst Solvent: Platinum metal (Pt) Solute: Hydrogen gas (H 2 ) Pt Concentration of solutions concentration -- the amount of solute dissolved in a given quantity of solvent or solution Concentration of solutions concentration -- the amount of solute dissolved in a given quantity of solvent or solution There are many different types of concentration units: molarity mass % volume % mass/volume % parts per million (ppm) parts per billion (ppb) mole fraction we will focus on this molality (not to be confused with molarity) These units are covered in the supplemental notes (posted on course website) molarity -- number of per liter of solution

3 Preparation of a 1 molar solution What is the molarity of a solution made by dissolving 2.00 g of potassium chlorate in enough water to make 150. ml of solution? Step 1: Start with the definition of molarity: Step 2: Determine the number of Molar mass of KClO 3 = (16.00) = g / mol 2.00 g KClO 3 1 mole KClO g KClO 3 = moles KClO 3 What is the molarity of a solution made by dissolving 2.00 g of potassium chlorate in enough water to make 150. ml of solution? What is the molarity of a solution made by dissolving 2.00 g of potassium chlorate in enough water to make 150. ml of solution? Step 3: Determine the number of liters of solution Step 4: Plug values into molarity equation 150. ml 1 liter 1000 ml = L moles KClO L moles KClO 3 / L = M KClO 3

4 How many grams of potassium hydroxide are required to prepare 600. ml of M KOH solution? How many grams of potassium hydroxide are required to prepare 600. ml of M KOH solution? Step 1: Start with the definition of molarity: Step 2: Determine the number of liters of solution 600. ml 1 liter 1000 ml = L Step 3: Plug known values into molarity equation and solve for unknown () M KOH = moles KOH 1 L solution = x moles of KOH L How many grams of potassium hydroxide are required to prepare 600. ml of M KOH solution? How many grams of potassium hydroxide are required to prepare 600. ml of M KOH solution? Step 3: Plug known values into molarity equation and solve for unknown () moles KOH x moles of KOH (0.600 L) = (0.600 L) 1 L L moles KOH = x Step 4: Convert moles KOH to grams KOH Molar mass of KOH = = g / mol g KOH moles KOH = 15.1 g KOH 1 mole KOH

5 Calculate the number of moles of nitric acid in 325 ml of 16 M HNO 3 Step 1: Start with the definition of molarity: Calculate the number of moles of nitric acid in 325 ml of 16 M HNO 3 Step 1: Start with the definition of molarity: Step 2: Plug known values into molarity equation and solve for unknown () Step 2: Plug known values into molarity equation and solve for unknown () 16 M HNO 3 = 16 moles HNO 3 1 L = x moles of HNO L (0.325 L) 16 moles HNO 3 1 L x moles of HNO 3 = (0.325 L) L 5.2 moles HNO 3 = x Dilutions Dilution: Reducing the concentration of a solution by adding more solvent to the solution More solvent is added: -- volume of the solution increases No additional solute is added -- number of stays the same Net result: The molarity of the solution decreases NO 3 - Na + Moles = 1.0 Volume = 1.0 L Molarity = 1.0 M Molarity (M) = (unchanged) NaNO 3 solution

6 Calculate the molarity of a solution prepared by diluting 125 ml of M HCl with 875 ml of water NO 3 - Na + Step 1: Start with the definition of molarity: Molarity (M) = Moles = 1.0 Volume = 2.0 L Molarity = 0.50 M Step 2: Plug in known values and solve for the unknown -- i.e., the number of contained in the initial volume of undiluted solution Solution volume is doubled (0.125 L) moles HCl L = x moles of HCl L (0.125 L) Moles of solute remain the same Solution concentration is halved moles HCl = x Calculate the molarity of a solution prepared by diluting 125 ml of M HCl with 875 ml of water Calculate the molarity of a solution prepared by diluting 125 ml of M HCl with 875 ml of water ALTERNATIVE METHOD (SHORTCUT): Use dilution factor based on initial solution volume and final solution volume Step 3: Calculate new molarity of solution based on final volume of solution after dilution Initial solution volume: L Final solution volume: L L = L Initial moles HCl: moles : L moles Molarity = L Molarity = M Final moles HCl: moles : L L = L moles Molarity = L Molarity = M initial volume L Dilution factor = = final volume L Final concentration = (dilution factor) x (initial concentration) L = M HCl = M HCl L

7 Acids and Bases Properties of acids 1. Sour taste 2. Changes the color of litmus from blue to red 3. Reacts with: metals (e.g., Zn and Mg) to produce hydrogen gas hydroxide bases (e.g., NaOH) to produce water and an ionic compound (salt) carbonates (e.g., CaCO 3 ) to produce CO 2 Examples of acids: lemon juice Vitamin C (ascorbic acid) vinegar (acetic acid) hydrochloric acid Properties of bases 1. Bitter taste 2. Slippery, soapy feel 3. Changes the color of litmus from red to blue 4. Reacts with acids Classical definition of acids and bases (Arrhenius) acid -- a substance that produces hydrogen ions (H + ) in aqueous solutions HCl H + (aq) + Cl - (aq) hydrochloric acid Examples of bases: ammonia -- NH 3 Milk of Magnesia -- Mg(OH) 2 sodium hydroxide -- NaOH base -- a substance that produces hydroxide ions (OH - ) in aqueous solutions NaOH Na + (aq) + OH - (aq) sodium hydroxide

8 Brønsted-Lowry acids and bases A Brønsted-Lowry acid is any substance that is able to give hydrogen ions (H + ) to another molecule or ion A Brønsted-Lowry base is any substance that accepts hydrogen ions (H + ) from another molecule or ion Brønsted-Lowry acids and bases A Brønsted-Lowry acid is a proton (H + ) donor : A Brønsted-Lowry base is a proton (H + ) acceptor : HCl (aq) + OH (aq) H 2 O (l) + Cl - (aq) acid base H O H NH 3 (l) + H 2 O (l) base acid conjugate acid-base pair NH 4 + (aq) + OH - (aq) acid base a Brønsted-Lowry acid is a proton (H + ) donor conjugate acid-base pair a Brønsted-Lowry base is a proton (H + ) acceptor The hydronium ion A hydrogen ion (H + ) does not exist by itself in an aqueous solution In water, H + combines with a polar H 2 O molecule to form a hydrated hydrogen ion (H 3 O + ) called a hydronium ion Naming acids Binary acids are formed from hydrogen and one other nonmetallic element Note: Not all binary compounds containing hydrogen are binary acids H + + H O H H O H H hydronium ion + HCl hydrochloric acid acid CH 4 methane not an acid If the binary compound is an acid, the H will appear first in the chemical formula

9 Binary compound both elements are nonmetals Naming binary acids the compound is an acid ( H appears first in formula ) Rule: The compound name is based on the stem of the nonhydrogen element Add hydro- before the stem and -ic after the stem, followed by the word acid Example: H + Cl - Naming polyatomic acids Polyatomic acids are made up of hydrogen and a polyatomic anion -- the chemical formula of a polyatomic acid begins with H -- the second part of the formula is a polyatomic anion containing oxygen (an oxy-anion) Rule: The name of a polyatomic acid is derived from its anion -- the ending of the anion name is modified -ate -ite -ic -ous -- the modified anion name is followed by the word acid Formula: HCl Elements: hydrogen (nonmetal) chlorine (nonmetal) Compound name: hydrochloric acid Example: HNO 3 anion: NO 3 anion name: nitrate modified anion name: nitrate polyatomic acid name: nitric acid nitric Naming polyatomic acids Naming bases Rule: The name of a polyatomic acid is derived from its anion -- the ending of the anion name is modified -ate -ic -ite -ous -- the modified anion name is followed by the word acid Acid Anion Anion name Acid name H 2 SO 4 SO 2-4 sulfate sulfuric acid H 2 SO 3 SO 2-3 sulfite sulfurous acid Common bases are formed from group 1A and 2A metals and the polyatomic hydroxide ion (OH ) These bases therefore follow the naming rules for polyatomic ions Rules: -- identify the ions -- name the cations in the order given -- follow them with the name of the anion Compound Cation(s) Anion Compound name KOH K + (potassium) OH (hydroxide) potassium hydroxide Ca(OH) 2 Ca 2+ (sodium) OH (hydroxide) calcium hydroxide

10 Reactions of acids and bases Neutralization reaction between an acid and a base in aqueous solutions, the products of a neutralization reaction are water and a salt Reactions of acids and bases Reactions between acids and carbonates similar to acid-base neutralization reaction the products are carbon dioxide, water, and a salt acid + base water + salt acid + carbonate carbon dioxide + water + salt H 2 SO 4 (aq) + MgCO 3 (s) H 2 CO 3 (aq) + MgSO 4 (aq) HBr (aq) + NaOH (aq) H 2 O (l) + NaBr (aq) Carbonic acid spontaneously decomposes into carbon dioxide and water H 2 CO 3 (aq) CO 2 (g) + H 2 O (l) Net reaction: H 2 SO 4 (aq) + MgCO 3 (s) CO 2 (g) + H 2 O (l) + MgSO 4 (aq) Homework Chapter 9 Problems: 9.38, 9.42, 9.48, 9.52, 9.62, 9.63, 9.64, 9.69, 9.73 Chapter 10 Problems: 10.47, 10.51, 10.52, 10.53