Chapter Types of Chemical Reactions and Solution Stoichiometry PHall AP info. NOT integrated into this presentation

Chapter Four: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY Sugar & Potassium Chlorate video not sure where it goes...

Chapter 4 Table of Contents Copyright © Cengage Learning. All rights reserved Water, the Common Solven4.1 Water, the Common Solvent 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolyte4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes 4.3 The Composition of Solution4.3 The Composition of Solutions 4.4 Types of Chemical Reaction4.4 Types of Chemical Reactions 4.5 Precipitation Reaction4.5 Precipitation Reactions

Section 4.1 Water, the Common Solvent Return to TOC Copyright © Cengage Learning. All rights reserved 3 One of the most important substances on Earth. Can dissolve many different substances. A polar molecule because of its unequal charge distribution.

Copyright © Houghton Mifflin Company. All rights reserved.4– Dissolution of a Solid in a Liquid Click here to watch video.

Solute A solute is the dissolved substance in a solution. A solvent is the dissolving medium in a solution. Solvent Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Water in salt waterWater in soda

“Like Dissolves Like” Fats Fats Benzene Benzene Steroids Steroids Hexane Hexane Waxes Waxes Toluene Toluene Polar and ionic solutes dissolve best in polar solvents Nonpolar solutes dissolve best in nonpolar solvents Inorganic Salts Water Water Sugars Sugars Small alcohols Small alcohols Acetic acid Acetic acid

Section 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Return to TOC Copyright © Cengage Learning. All rights reserved 5 Solute – substance being dissolved. Solvent – liquid water. Electrolyte – substance that when dissolved in water produces a solution that can conduct electricity. Nature of Aqueous Solutions

Section 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Return to TOC Copyright © Cengage Learning. All rights reserved 6 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). Electrolytes

Copyright © Houghton Mifflin Company. All rights reserved.4– Electrolytes click here to watch video.

Copyright © Houghton Mifflin Company. All rights reserved.4– Electrolyte Behavior Click here to watch visualization.

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. Definition of Electrolytes and 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. Electrolytes vs. Nonelectrolytes

1.Pure water 2.Tap water Sugar solution Sodium chloride solution Hydrochloric acid solution Lactic acid solution Ethyl alcohol solution Pure sodium chloride 1.Pure water 2.Tap water Sugar solution Sodium chloride solution Hydrochloric acid solution Lactic acid solution Ethyl alcohol solution Pure sodium chloride Try to classify the following substances as electrolytes or nonelectrolytes…

ELECTROLYTES: NONELECTROLYTES: Tap water (weak) NaCl solution HCl solution Lactate solution (weak) Pure water Sugar solution Ethanol solution Pure NaCl Answers to Electrolytes

Ionic Compounds “Dissociate” NaCl(s)  AgNO 3 (s)  MgCl 2 (s)  Na 2 SO 4 (s)  AlCl 3 (s)  Na + (aq) + Cl - (aq) Ag + (aq) + NO 3 - (aq) Mg 2+ (aq) + 2 Cl - (aq) 2 Na + (aq) + SO 4 2- (aq) Al 3+ (aq) + 3 Cl - (aq)

The reason for this is the 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). Ions tend to stay in solution where they can conduct a current rather than re-forming a solid.

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 (H 3 O + ). Some covalent compounds IONIZE in solution

Other examples of strong acids include:  Sulfuric acid, H 2 SO 4  Nitric acid, HNO 3  Hydriodic acid, HI  Perchloric acid, HClO 4 Strong acids such as HCl are completely ionized in solution.

Many of these weaker acids are “organic” acids that contain a “carboxyl” group. The carboxyl group does not easily give up its hydrogen. Weak acids such as lactic acid usually ionize less than 5% of the time.

Other organic acids and their sources include: o Citric acid – citrus fruit o Malic acid – apples o Butyric acid – rancid butter o Amino acids – protein o Nucleic acids – DNA and RNA o Ascorbic acid – Vitamin C This is an enormous group of compounds; these are only a few examples. Because of the carboxyl group, organic acids are sometimes called “carboxylic acids”.

SolutionsSolutionsSolutionsSolutions solutionsxt

Solution Concentration

Calculations of Solution Concentration: Molarity Molarity Molarity is the ratio of moles of solute to liters of solution

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 8 We must know:  The nature of the reaction.  The amounts of chemicals present in the solutions. Chemical Reactions of Solutions

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 9 Molarity (M) = moles of solute per volume of solution in liters: Molarity

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 10 Exercise A 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

Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of M NaCl solution?  Step #1: Ask “How Much?” (What volume to prepare?) L  Step #2: Ask “How Strong?” (What molarity?) mol 1 L  Step #3: Ask “What does it weigh?” (Molar mass is?) g 1 mol = 43.8 g

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 11 For a 0.25 M CaCl 2 solution: CaCl 2 → Ca Cl –  Ca 2+ : 1 × 0.25 M = 0.25 M Ca 2+  Cl – : 2 × 0.25 M = 0.50 M Cl –. Concentration of Ions 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.

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 12 Concept Check Which of the following solutions contains the greatest number of ions? a) mL of 0.10 M NaCl. b) mL of 0.10 M CaCl 2. c) mL of 0.10 M FeCl 3. d) mL of 0.10 M sucrose.

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 13 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? Let’s Think About It

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 14 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. Notice

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 15 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 M 1 V 1 = M 2 V 2 Dilution

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 16 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? a) Add water to the solution. b) Pour some of the solution down the sink drain. c)Add more sodium chloride to the solution. d)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.

Serial Dilution Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? M stock V stock = M dilute V dilute (11.6 M)(x Liters) = (3.0 M)(0.250 Liters) x Liters = (3.0 M)(0.250 Liters) 11.6 M = L

Copyright © Houghton Mifflin Company. All rights reserved.4– Dilution Click here to watch video

Section 4.3 The Composition of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 17 Exercise What is the minimum volume of a 2.00 M NaOH solution needed to make mL of a M NaOH solution? 60.0 mL

Section 4.4 Types of Chemical Reactions Return to TOC Copyright © Cengage Learning. All rights reserved 18 Precipitation Reactions Acid–Base Reactions Oxidation–Reduction Reactions

Precipitation Reactions Graphic: Wikimedia Commons User Tubifex

Section 4.5 Precipitation Reactions Return to TOC Copyright © Cengage Learning. All rights reserved 19 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. Precipitation Reaction

Section 4.5 Precipitation Reactions Return to TOC Copyright © Cengage Learning. All rights reserved 20 Ba 2+ (aq) + CrO 4 2– (aq) → BaCrO 4 (s) The Reaction of K 2 CrO 4 (aq) and Ba(NO 3 ) 2 (aq)

Copyright © Houghton Mifflin Company. All rights reserved.4– Precipitation of Silver Chloride Click here to watch visualization

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… Pb(NO 3 ) 2 (aq) + 2KI(aq)  PbI 2 (s) + 2KNO 3 (aq) Pb 2+ (aq) + 2 NO 3 - (aq) + 2 K + (aq) +2 I - (aq)  PbI 2 (s) + 2K + (aq) + 2 NO 3 - (aq) Pb 2+ (aq) + 2 I - (aq)  PbI 2 (s) Double replacement (ionic) equation Complete ionic equation shows compounds as aqueous ions Net ionic equation eliminates the spectator ions Lead(II) nitrate + potassium iodide →  lead(II) iodide + potassium nitrate

Solubility Rules – Mostly Soluble IonSolubilityExceptions NO 3 - SolubleNone ClO 4 - SolubleNone Na + SolubleNone K+K+K+K+SolubleNone NH 4 + SolubleNone Cl -, I - Soluble Pb 2+, Ag +, Hg 2 2+ SO 4 2- Soluble Ca 2+, Ba 2+, Sr 2+, Pb 2+, Ag +, Hg 2+

Solubility Rules – Mostly Insoluble IonSolubilityExceptions CO 3 2- Insoluble Group IA and NH 4 + PO 4 3- Insoluble Group IA and NH 4 + OH - Insoluble Group IA and Ca 2+, Ba 2+, Sr 2+ S 2- Insoluble Groups IA, IIA, and NH 4 +

Copyright © Houghton Mifflin Company. All rights reserved.4– 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.

Solubility Chart: Common salts at 25  C S = Soluble I = Insoluble P = Partially Soluble X = Other

Section 4.5 Precipitation Reactions Return to TOC Copyright © Cengage Learning. All rights reserved 22 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. Precipitates

Section 4.5 Precipitation Reactions Return to TOC Copyright © Cengage Learning. All rights reserved Most nitrate (NO 3 − ) salts are soluble. 2. Most alkali metal (group 1A) salts and NH 4 + are soluble. 3. Most Cl −, Br −, and I − salts are soluble (except Ag +, Pb 2+, Hg 2 2+ ). 4. Most sulfate salts are soluble (except BaSO 4, PbSO 4, Hg 2 SO 4, CaSO 4 ). 5. Most OH − are only slightly soluble (NaOH, KOH are soluble, Ba(OH) 2, Ca(OH) 2 are marginally soluble). 6. Most S 2−, CO 3 2−, CrO 4 2−, PO 4 3− - salts are only slightly soluble, except for those containing the cations in Rule 2. Simple Rules for Solubility

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 Return to TOC Copyright © Cengage Learning. All rights reserved 24 Concept Check Which of the following ions form compounds with Pb 2+ that are generally soluble in water? a)S 2– b)Cl – c)NO 3 – d)SO 4 2– e)Na +

57 Section 4.5 Precipitation Reactions Return to TOC END OF SLIDES FOR SECTION