Chemistry 101 1st Edition Exam 4 Study Guide Chapters 8 10 Lecture 1 Chapter 8 Limiting Reagents and Theoretical Yield Calculate limiting reagents theoretical yields and actual yields Pgs 283 289 Chemical Reactions and Stoichiometry Limiting reagents is the amount of a reactant that limits the amount of product that can be made o Ex 2 H 2 O 2 2 H 2 O The chemical equation states that 2 equivalents of H 2 react with 1 equivalent of O 2 Therefore if there are 2 equivalents of both H 2 and O2 present H 2 would be the limiting reagent o Ex Cars on an assembly line Every car needs 4 wheels and 1 steering wheel If you have 3 steering wheels and 8 tires you can only make 2 cars because you only have enough tires for 2 cars Thus tires are the limiting reagent To find which reactant is the limiting reagent follow these steps 1 Balance equation 2 Use stoichiometry to determine how much product can be made from reactant A 3 Use stoichiometry to determine how much product can be made from reactant B 4 The reactant with the smaller amount of product is the limiting reactant Theoretical Yield Theoretical yield is the maximum amount of product that can be made based on the limiting reagent Found using stoichiometry Actual yield is the amount of product actually produced in the reaction Percent yield is o actual yield percent yield x 100 practice The burning of 9 20 g of CH 4 with excess O 2 produces 11 0 g of H 2 O What is the theoretical yield and percent yield Equation CH 4 g 2O 2 g CO2 g 2 H 2 O g Answer theoretical yield 20 68 g of H 2 O Percent yield 53 19 Lecture 2 Chapter 9 Introduction to Solutions Define a solution Calculate the concentration of a solution Use concentrations to determine molar and mass quantities Pgs 301 307 Solutions A solution is a homogenous mixture that contains two parts o A solvent the major component the dissolver o One or more solute the minor component the dissolved If you add sugar or table salt to a glass of water the sugar or salt dissolves completely thus forming a solution Solutions with water as the solvent are called aqueous solutions Solution Concentration The concentration of solution is in units of mass volume In chemistry we use molarity which is mol L o Molarity M amount of solute in mols amount of solvent in liters mol L Example Molarity of 3 5 mols of NaCl dissolved in 7 0 L of water 3 5mol 7 0Lwater 0 5 M How to make a solution If you combine 1 mol NaCl with 1 L of water the concentration will NOT be 1M o Why Adding NaCl will increase the volume of the solution Therefore to make a 1M solution o Add 1 mol of NaCl o Add enough water to dissolve NaCl o Dilute with more water until volume is 1 L Diluting Solutions M 1 V 1 M 2 V 2 this is the equation to use when diluting solutions What is the final concentration of 1 0 L of 2 0M HCl if solution diluted to 2 0L o 1 0L x 2 0M 2 0L 1 0M HCl o move around the numbers so all known numbers are on one side Lecture 3 Chapter 9 The dissolution process and solubility Qualitatively describe the dissolution process Explain the difference between electrolytes and non electrolytes Identify the key characteristics of strong electrolytes and weak electrolytes Use a solubility table to predict solution phase reactions pgs 308 313 When table salt dissolves in water it completely disassociates and is surrounded by water This makes it a good electrolyte If an ionic compound dissolves in water it will be an electrolyte This also means that it can conduct electricity in solution Strong electrolyte 100 disassociation o HCl H Cl Weak electrolyte less than 100 disassociation o CH 3 CO 2 H CH CO H 3 2 When ionic compounds dissolve in water the anions and cations are separated from each other This is called dissociation When compounds containing polyatomic ions dissociate the polyatomic group stays together as one ion THIS IS KEY TO REMEMBER Nonelectrolytes Most molecular compounds except acids are nonelectrolytes in solution Nonelectrolytes DO NOT disassociate Solubility Some ionic compounds like NaCl dissolve well in water at room temperature Others like AgCl do not Why Compounds that dissolve are soluble and those that do not are insoluble Predicting this is not easy however the best way to figure is to do experiments and come with a rule Know these tables When two soluble compounds are mixed together and two of the ions are soluble when together there will be a precipitate When no precipitate is formed there is no reaction Predicting Precipitation Reactions 1 determine what ions each aqueous reaction has 2 determine formulas of possible products a exchange ions i ion from reactant with ion from other b balance charges of combined ions to get formula of each product 3 determine solubility of each product in water a use the solubility rules b if product is insoluble or slightly soluble it will precipitate 4 if neither product will precipitate write no reaction after arrow 5 if any of the possible products are insoluble write their formulas as the products of the reactions using s after the formula to indicate solid Write any soluble products with aq after formula to indicate aqueous 6 balance the equation a remember to only change coefficients not subscripts Lecture 4 Chapter 9 Ionic Equations write complete ionic equation write a net ionic equation pgs 318 319 Molecular Equations equations that describe the chemicals put into the water and the product molecules formed are called molecular equations Complete Ionic Equations equations that describe the material s structure when dissolved are called complete ionic equations draw each individual soluble ion and emphasize what state it is in all strong electrolytes are written as ions insoluble substances and weak electrolytes and non electrolytes are written in molecular formula Net Ionic Equations Ions that are both reactants and products are called spectator ions An ionic equation in which the spectator ions are removed is called a net ionic equation Lecture 5 Chapter 9 Acid Base reactions and Titrations Understand how an acid and base react Calculate acid base concentration via titration Acids and Bases in Solution Acids ionize in water to form H ions o HI H I Bases dissociate in water to form OH ions Acid Base fun In the reaction of an acid with a base the H from the acid combines with the OH from the base to make water The cation from the base combines with the anion from the acid to form the sale o Acid base salt water Titration Often in the lab a solution s