CHE 101 Lecture Outline Chapter 4 Chapter 4 Aqueous Reactions Molarity What Happens to Solid Chemicals when they Dissolve Solids exist in a crystal lattice repeating pattern of ions or molecules Salt NaCl Sugar C12H22O11 Sucrose Ions Molecules Hydration water molecules break apart the crystal lattice of solids 2 Types of break ups Dissolved molecules Ex sucrose 1 Break apart into individual molecules Occurs when the chemical is molecular 2 Break apart into ions a process called Dissociation Occurs when the chemical is ionic acidic or basic Dissolved ions Ex Na Cl Resulting in an electrolyte solution 1 CHE 101 Lecture Outline Chapter 4 Electrolytes Electrolytes a chemical dissolved in water that conducts electricity due to the presence of IONS High conductance values means more ions Which substance will conduct more The one with more ions Dissociation equations determines which ions are present How to write separate into ions place charges above symbols then balance NaCl aq Na aq Cl aq Ca3 PO4 2 aq 2 Total ions 5 Total ions Types of Electrolytes 1 Strong Electrolytes high conductance Many ions 100 dissociation Made up of Ionic compounds Strong acids Strong bases 2 Weak Electrolytes low conductance Few ions Partial dissociation More molecules than ions present Made up of Weak acids Weak bases 3 Non electrolytes No conductance No ions No dissociation Made up of Molecular compounds 2 CHE 101 Lecture Outline Chapter 4 Acid Base Definitions Acids Always produce a proton H ion Usually either start w H or end w COOH Protons available active in an acid of FRONT H s HCl 1 H H3PO4 3 H HC2H3O2 1 H Bases Always produce a hydroxide OH ion 3 CHE 101 Lecture Outline Chapter 4 STRONG Acid Bases They dissociate 100 thus strong electrolytes Use 1 way arrow in dissociation eq Strong acids MEMORIZE LIST Strong bases MEMORIZE LIST WEAK Acids Bases Dissociate partially 100 thus weak electrolytes Breaks into ions but also reforms original molecule More original molecules present Use 2 way arrow Weak acids NOT on strong list Weak bases many exist but memorize NH3 in dissociation eq Caution NH4 is not a base 4 CHE 101 Lecture Outline Chapter 4 Questions 4 2 Indicate the type of Electrolyte for SrF2 A Strong B Weak C Non 4 3 Indicate the type of Electrolyte for NH4Br A Strong B Weak C Non 4 4 Which chemical will conduct more A SrF2 B NH4Br C The conduct the same Types of Reactions Many reactions have characteristics in common 5 Basic types 1 Combination 2 Decomposition 3 Combustion 4 Single Replacement 5 Double Replacement NOTE When forming products move subscripts unless a ion How to Write a Balanced Equation Extended 1 Write correct chemical formulas If an compound or an use IONS Positive ion written first 2 Add to all chemicals See next 3 Balance each element by adjusting coefficients Smallest whole numbers are preferred 5 CHE 101 Lecture Outline Chapter 4 How to Predict Phases 1 Metals solids 2 Diatomics gases 3 Acids 4 Solutions 5 Water Unless specified 6 Solubility Rules Soluble will dissolve aq What is the phase of CaBr2 aq Al2S3 s PbI2 s MUST know ions that are soluble 6 CHE 101 Lecture Outline Chapter 4 SINGLE Replacement Rxns Single Replacement a free element in natural state substitutes for the cation in a different compound 2 Fe s 3 CdCl2 aq 2 FeCl 3 aq 3 Cd s Sample Problems Write a balanced eq A 2Al s 6HC2H3O2 aq 2Al C2H3O2 3 aq 3H2 g B Ca s Na3PO4 aq Ca2 PO43 Na 3Ca s 2Na3PO4 aq Ca3 PO4 2 s 6Na s DOUBLE Replacement Rxns LAB 3 Double Replacement cation from one compound interacts with the anion from the other compound Aka Metathesis rxn 3MgCl 2 aq 2 K 3 PO 4 aq Mg 3 PO 4 2 s 6KCl aq There are many types of double replacement rxns 1 Precipitation Rxn double replacement 7 CHE 101 Lecture Outline Chapter 4 Precipitation Rxn 2 compounds react to form an insoluble solid compound aka precipitate Looks cloudy Cu NO3 3 aq NH4 2CO3 aq Cu3 CO32 NH4 NO32Cu NO3 3 aq 3 NH4 2CO3 aq Cu2 CO3 3 s 6NH4NO3 aq 2 Neutralization Rxn double replacement Neutralization rxn Acid aq Base aq H 2 O l salt Salt any ionic compound HI aq Ca OH 2 aq Ca2 I H OH2HI aq Ca OH 2 aq CaI2 aq 2H2O l 3 Unstable product double replacement Sometimes an unstable compound is produced This compound immediately decomposes into new chemicals a H2CO3 CO2 g H2O l b H2SO3 SO2 g H2O l K2CO3 aq HCl aq K Cl H CO32K2CO3 aq HCl aq KCl aq H2CO3 aq UNSTABLE K2CO3 aq 2HCl aq 2KCl aq CO2 g H2O l 8 CHE 101 Lecture Outline Chapter 4 Descriptive Equations Lab 3 You ve just learned to write balance Molecular chemical equations Ex Since chemicals are dissolved in water many will dissociate Can re write equations to indicate what s actually in the containers Complete or Total Ionic Equations Complete Total Ionic eq rewrites molecular equation showing 100 dissociation Only break apart chemicals that meets BOTH criteria 1 Aqueous 2 STRONG electrolyte Net Ionic Equations Net Ionic eq rewrites Complete Ionic equation by cancelling out the spectators Spectators look EXACTLY the same on BOTH sides of the equation They do NOT participate in the reaction Shows what s actually chemically reacting Spectators NO3 NH4 NOTE If everything cancels NO RXN occurs 9 CHE 101 Lecture Outline Chapter 4 10 CHE 101 Lecture Outline Chapter 4 What does this look like Molecular 2Cu NO3 3 aq 3 NH 4 2 CO 3 aq Cu 2 CO3 3 s 6NH4 NO3 aq Complete Ionic Sample Problem 1 2Al s 3H2SO4 aq Entire Problem In Notes Complete Ionic Net Ionic 11 CHE 101 Lecture Outline Chapter 4 What is a Solution Solution Soln uniform mixture of 2 or more substances SOLUTE SOLVENT Solute usually present in a smaller amounts It is being dissolved Solvent usually present in a larger amounts In aqueous solutions it is H2O Concentration Molarity M mols of solute per liter of solution mols M L Many ways of expressing the molarity unit A Solution of 0 901 mols NaCl per liter of water is 0 901 mols L or 0 901 M or 0 901 molar 12 CHE 101 Lecture Outline Chapter 4 Sample Problems 1 Calculate the molarity of 1 42g of Al NO3 3 in 15 4mL of water IN NOTEBOOK 2 Calculate the molar concentration of Al3 and NO3 ions in the previous problem Look at notes in notebook 13 CHE 101 Lecture Outline Chapter 4 Molarity Cont d It is a fraction and has 2 units therefore it is a conversion factor Never start calculations w a conversion factor Exact or inexact 14 CHE 101 Lecture Outline Chapter 4 Sample Problems 3 How many liters are required to dissolve 3 052g of HCl in order to make a 0 540 M solution Look at notes in notebook 4 How many