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PHall AP info. NOT integrated into this presentation Chapter 4.1-4.5 Types of Chemical Reactions and Solution Stoichiometry Sugar & Potassium Chlorate video not sure where it goes... Chapter Four: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY Chapter 4 Table of Contents 4.1 4.2 4.3 4.4 4.5 Water, the Common Solvent The Nature of Aqueous Solutions: Strong and Weak Electrolytes The Composition of Solutions Types of Chemical Reactions Precipitation Reactions Copyright © Cengage Learning. All rights reserved 2 Section 4.1 Water, the Common Solvent • • • One of the most important substances on Earth. Can dissolve many different substances. A polar molecule because of its unequal charge distribution. Return to TOC Copyright © Cengage Learning. All rights reserved 3 Dissolution of a Solid in a Liquid Click here to watch video. Copyright © Houghton Mifflin Company. All rights reserved. 4– Solute A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda “Like Dissolves Like” Nonpolar solutes dissolve best in nonpolar solvents Fats Benzene Steroids Hexane Waxes Toluene Polar and ionic solutes dissolve best in polar solvents Inorganic Salts Water Sugars Small alcohols Acetic acid Section 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Nature of Aqueous Solutions • • • Solute – substance being dissolved. Solvent – liquid water. Electrolyte – substance that when dissolved in water produces a solution that can conduct electricity. Return to TOC Copyright © Cengage Learning. All rights reserved 5 Section 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Electrolytes • • • Strong Electrolytes – conduct current very efficiently (bulb shines brightly). Weak Electrolytes – conduct only a small current (bulb glows dimly). Nonelectrolytes – no current flows (bulb remains unlit). Return to TOC Copyright © Cengage Learning. All rights reserved 6 Electrolytes click here to watch video. Copyright © Houghton Mifflin Company. All rights reserved. 4– Electrolyte Behavior Click here to watch visualization. Copyright © Houghton Mifflin Company. All rights reserved. 4– Definition of Electrolytes and Nonelectrolytes An electrolyte is: A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current. Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting. Try to classify the following substances as electrolytes or nonelectrolytes… 1.Pure water 2.Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure sodium chloride Answers to Electrolytes ELECTROLYTES: NONELECTROLYTES: Tap water (weak) Pure water NaCl solution Sugar solution • HCl solution • Lactate solution (weak) • Ethanol solution • Pure NaCl Ionic Compounds “Dissociate” Na+(aq) + Cl-(aq) NaCl(s) +(aq) + NO -(aq) Ag AgNO3(s) 3 Mg2+(aq) + 2 Cl-(aq) MgCl2(s) 2 Na+(aq) + SO42-(aq) Na2SO4(s) AlCl3(s) Al3+(aq) + 3 Cl-(aq) solution where they can conduct a current rather than re-forming a The reason for this is the solid. polar nature of the water molecule… Positive ions associate with the negative end of the water dipole (oxygen). Negative ions associate with the positive end of the water dipole (hydrogen). Some covalent compounds IONIZE in solution Covalent acids form ions in solution, with the help of the water molecules. For instance, hydrogen chloride molecules, which are polar, give up their hydrogens to water, forming chloride ions (Cl-) and hydronium ions (H3O+). Strong acids such as HCl are completely ionized in solution. Other examples of strong acids include: Sulfuric acid, H2SO4 Nitric acid, HNO3 Hydriodic acid, HI Perchloric acid, HClO4 Weak acids such as lactic acid usually ionize less than 5% of the time. Many of these weaker acids are “organic” acids that contain a “carboxyl” group. The carboxyl group does not easily give up its hydrogen. Because of the carboxyl group, organic acids are sometimes called “carboxylic acids”. Other organic acids and their sources include: o o o o o o Citric acid – citrus fruit Malic acid – apples Butyric acid – rancid butter Amino acids – protein Nucleic acids – DNA and RNA Ascorbic acid – Vitamin C This is an enormous group of compounds; these are only a few examples. S o l u t i o n s solutionsxt Solution Concentration Calculations of Solution Concentration: Molarity Molarity is the ratio of moles of solute to liters of solution Section 4.3 The Composition of Solutions Chemical Reactions of Solutions • We must know: The nature of the reaction. The amounts of chemicals present in the solutions. Return to TOC Copyright © Cengage Learning. All rights reserved 8 Section 4.3 The Composition of Solutions Molarity • Molarity (M) = moles of solute per volume of solution in liters: Return to TOC Copyright © Cengage Learning. All rights reserved 9 Section 4.3 The Composition of Solutions Exercise A 500.0-g sample of potassium phosphate is dissolved in enough water to make 1.50 L of solution. What is the molarity of the solution? (calculate #moles per L to get molarity) 1.57 M Return to TOC Copyright © Cengage Learning. All rights reserved 10 Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution? Step #1: Ask “How Much?” (What volume to prepare?) Step #2: Ask “How Strong?” (What molarity?) Step #3: Ask “What does it weigh?” (Molar mass is?) 1.500 L 0.500 mol 58.44 g 1 L 1 mol = 43.8 g Section 4.3 The Composition of Solutions Concentration of Ions • For a 0.25 M CaCl2 solution: CaCl2 → Ca2+ + 2Cl– Ca2+: 1 × 0.25 M = 0.25 M Ca2+ Cl–: 2 × 0.25 M = 0.50 M Cl–. Note that there were 2 times as many ions of Cl- formed, so the molarity was doubled due to having twice as many moles like in the titration lab with citric acid which had 3 moles hydrogen ions produced for each mole of the base. Return to TOC Copyright © Cengage Learning. All rights reserved 11 Section 4.3 The Composition of Solutions Concept Check Which of the following solutions contains the greatest number of ions? a) b) c) d) 400.0 mL of 0.10 M NaCl. 300.0 mL of 0.10 M CaCl2. 200.0 mL of 0.10 M FeCl3. 800.0 mL of 0.10 M sucrose. Return to TOC Copyright © Cengage Learning. All rights reserved 12 Section 4.3 The Composition of Solutions Let’s Think About It • Where are we going? • To find the solution that contains the greatest number of moles of ions. How do we get there? Draw molecular level pictures showing each solution. Think about relative numbers of ions. How many moles of each ion are in each solution? Return to TOC Copyright © Cengage Learning. All rights reserved 13 Section 4.3 The Composition of Solutions Notice • The solution with the greatest number of ions is not necessarily the one in which: the volume of the solution is the largest. the formula unit has the greatest number of ions. Return to TOC Copyright © Cengage Learning. All rights reserved 14 Section 4.3 The Composition of Solutions Dilution • • • The process of adding water to a concentrated or stock solution to achieve the molarity desired for a particular solution. Dilution with water does not alter the numbers of moles of solute present. Moles of solute before dilution = moles of solute after dilution M1V1 = M2V2 Return to TOC Copyright © Cengage Learning. All rights reserved 15 Section 4.3 The Composition of Solutions Concept Check A 0.50 M solution of sodium chloride in an open beaker sits on a lab bench. Which of the following would decrease the concentration of the salt solution? Add water to the solution. Pour some of the solution down the sink drain. Add more sodium chloride to the solution. Let the solution sit out in the open air for a couple of days. e) At least two of the above would decrease the concentration of the salt solution. a) b) c) d) Copyright © Cengage Learning. All rights reserved Return to TOC 16 Serial Dilution Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? MstockVstock = MdiluteVdilute (11.6 M)(x Liters) = (3.0 M)(0.250 Liters) x Liters = (3.0 M)(0.250 Liters) 11.6 M = 0.065 L Dilution Click here to watch video Copyright © Houghton Mifflin Company. All rights reserved. 4– Section 4.3 The Composition of Solutions Exercise What is the minimum volume of a 2.00 M NaOH solution needed to make 150.0 mL of a 0.800 M NaOH solution? 60.0 mL Return to TOC Copyright © Cengage Learning. All rights reserved 17 Section 4.4 Types of Chemical Reactions • • • Precipitation Reactions Acid–Base Reactions Oxidation–Reduction Reactions Return to TOC Copyright © Cengage Learning. All rights reserved 18 Precipitation Reactions Graphic: Wikimedia Commons User Tubifex Section 4.5 Precipitation Reactions Precipitation Reaction • A double displacement reaction in which a solid forms and separates from the solution. When ionic compounds dissolve in water, the resulting solution contains the separated ions. Precipitate – the solid that forms. Return to TOC Copyright © Cengage Learning. All rights reserved 19 Section 4.5 Precipitation Reactions The Reaction of K2CrO4(aq) and Ba(NO3)2(aq) • Ba2+(aq) + CrO42–(aq) → BaCrO4(s) Return to TOC Copyright © Cengage Learning. All rights reserved 20 Precipitation of Silver Chloride Click here to watch visualization Copyright © Houghton Mifflin Company. All rights reserved. 4– Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. AX + BY AY + BX One of the compounds formed is usually a precipitate (an insoluble solid), an insoluble gas that bubbles out of solution, or a molecular compound, usually water. Double replacement forming a precipitate… Lead(II) nitrate + potassium iodide lead(II) iodide + potassium nitrate Double replacement (ionic) equation Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq) Complete ionic equation shows compounds as aqueous ions Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq) PbI2(s) + 2K+(aq) + 2 NO3-(aq) Net ionic equation eliminates the spectator ions Pb2+(aq) + 2 I-(aq) PbI2(s) Solubility Rules – Mostly Soluble Ion Solubility Exceptions NO3- Soluble None ClO4- Soluble None Na+ Soluble None K+ Soluble None NH4+ Soluble None Cl-, I- Soluble Pb2+, Ag+, Hg22+ SO42- Soluble Ca2+, Ba2+, Sr2+, Pb2+, Ag+, Hg2+ Solubility Rules – Mostly Insoluble Ion Solubility Exceptions CO32- Insoluble Group IA and NH4+ PO43- Insoluble Group IA and NH4+ OH- Insoluble Group IA and Ca2+, Ba2+, Sr2+ S2- Insoluble Groups IA, IIA, and NH4+ Table 4.1 Simple Rules for the Solubility of Salts in Water Copyright © Houghton Mifflin Company. All rights reserved. 4– Solubility Rules Click here to watch video. Copyright © Houghton Mifflin Company. All rights reserved. 4– Solubility Chart: Common salts at 25C S = Soluble I = Insoluble P = Partially Soluble X = Other Section 4.5 Precipitation Reactions Precipitates • • • Soluble – solid dissolves in solution; (aq) is used in reaction. Insoluble – solid does not dissolve in solution; (s) is used in reaction. Insoluble and slightly soluble are often used interchangeably. Return to TOC Copyright © Cengage Learning. All rights reserved 22 Section 4.5 Precipitation Reactions Simple Rules for Solubility 1. Most nitrate (NO3) salts are soluble. 2. Most alkali metal (group 1A) salts and NH4+ are soluble. 3. Most Cl, Br, and I salts are soluble (except Ag+, Pb2+, Hg22+). 4. Most sulfate salts are soluble (except BaSO4, PbSO4, Hg2SO4, CaSO4). 5. Most OH are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble). 6. Most S2, CO32, CrO42, PO43- salts are only slightly soluble, except for those containing the cations in Rule 2. Return to TOC Copyright © Cengage Learning. All rights reserved 23 Solubility Trends The solubility of MOST solids increases with temperature. The rate at which solids dissolve increases with increasing surface area of the solid. The solubility of gases decreases with increases in temperature. The solubility of gases increases with the pressure above the solution. Therefore… Solids tend to dissolve best when: o Heated o Stirred o Ground into small particles Gases tend to dissolve best when: o The solution is cold o Pressure is high Solubility Chart Saturation of Solutions A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. A solution that contains less solute than a saturated solution under existing conditions is unsaturated. A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated. Section 4.5 Precipitation Reactions Concept Check Which of the following ions form compounds with Pb2+ that are generally soluble in water? a) b) c) d) e) S2– Cl– NO3– SO42– Na+ Return to TOC Copyright © Cengage Learning. All rights reserved 24 Section 4.5 Precipitation Reactions END OF SLIDES FOR SECTION 4.1-4.5 • END OF SLIDES FOR SECTION 4.1-4.5 Return to TOC 57