Chapter 4 Chemistry 1A Page 1 Chapter 4 Chemical Quantities and Aqueous Reactions Homework Read Chapters 4 Work out sample practice exercises Bonus Chapter 4 Problems 25 31 37 43 49 53 57 59 63 67 69 73 77 79 83 87 89 93 95 101 Check MasteringChemistry com assignment and complete before due date Reaction Stoichiometry Chemical arithmetic Stoichiometry is the study of numerical relationships between chemical quantities in a chemical reaction Using ratios found in balanced chemical reactions to solve quantitative problems Convert to moles mole to mole ratio convert to desired result Practice 1 Balance the equation below and calculate the mass in grams of water vapor produced when 56 0 g of pure hydrogen gas burns in an unlimited supply of oxygen H2 g O2 g H2O g 2 How many mg of solid iron III chloride FeCl3 result when 15 5 milligrams of solid iron Fe is reacted with an excess of chlorine gas Cl 2 Start by balancing the equation Chapter 4 Chemistry 1A Page 2 Yields Actual or Experimental Yield that produced in a lab environment Theoretical Yield the highest maximum possible yield assuming 100 perfection using up all of the limiting reactant Percent Yield x 100 Limiting reactants The limiting reactant is completely consumed producing the least amount of product It runs out first and limits the amount of product It produces the lowest maximum theoretical yield Limiting reactant problems occur when two values for reactants are given Excess reactants Excess reactants are not completely consumed in the reaction Practice 3 a Balance the following unbalanced equation BaO s 4 HCl aq BaCl2 aq H2O l b There are 2 moles of BaO and 2 moles of HCl which is the limiting reactant a Balance the following unbalanced equation Ca s b c d H2O l Ca OH 2 aq H2 g How many grams of H2O would be required to react with 8 00 g of calcium Solve for the theoretical mass of hydrogen gas produced When the reaction described above was carried out in the lab 0 346 grams of hydrogen gas was obtained Calculate the percent yield for this reaction Chapter 4 5 a c d Page 3 Balance the following unbalanced equation P4 s b Chemistry 1A F2 g PF5 g Calculate the theoretical mass in grams of phosphorus pentafluoride produced from 12 6 grams F2 and 9 00 g phosphorus What is the limiting reactant from the reaction above What is the yield of the reaction above if 15 8g of PF 5 were experimentally produced in a lab starting with the given amounts above Solution Concentrations Homogenous mixtures are called solutions The major component that keeps its same state is called the solvent The minor component the one that may have a change in state is the solute Dilute solutions have a small amount of solute concentrated solutions have a large amount of solute compared to the solvent Molarity moles of solute liter of solution Molarity can be used as a conversion factor to solve for moles in stoichiometry problems Solution Dilution M1V1 M2V2 When diluting solutions it is best to use a volumetric flask and safest to start with some solvent then add the concentrated amount followed by more solvent to reach the desired total volume Note Volumes are not always additive for example 50 ml of water plus 50 ml of ethanol only produce 95 ml volume total due to some differences in density and intermolecular attractions Other concentrations for solutions include mass percent volume percent mass volume percent ppm ppb normality molality mole fraction Chapter 4 Chemistry 1A Page 4 Practice 6 Calculate the Molarity of a solution made from 30 0 grams of sucrose C12H22O11 added to enough water to make 300 ml total solution 7 Describe quantitatively and qualitatively how one should safely prepare 500 ml of 1 0 M H2SO4 aq solution from 18 0 M H2SO4 stock solution 8 How many grams of hydrogen gas will be theoretically formed by the reaction of 10 0 ml of 6 00 M HCl with excess zinc Zn s HCl aq ZnCl2 aq H2 g unbalanced Chapter 4 Chemistry 1A Page 5 Titrations In a titration a substance in a solution of known concentration is reacted with another of unknown concentration A burette is used to add a known volume to a flask with an indicator that will change endpoint when the reactants reach their stoichiometric ratio equivalence point Practice 9 Solve for the molarity concentration in a 10 0 ml portion of acetic acid solution HC2H3O2 that required 39 6 ml of 0 202 M NaOH solution to reach the equivalence point in a titration Chapter 4 Chemistry 1A Page 6 Gas Stoichiometry Molar volume at STP for any ideal gas is 22 4 L mol STP standard temperature 0 C and pressure 1 atmosphere Practice 10 Pure iron may be prepared from iron III oxide and carbon monoxide Fe2O3 s CO g Fe s CO2 g a Balance the unbalanced equation above b Calculate the maximum theoretical mass in grams of Fe produced from 40 0 L of carbon monoxide at STP from the reaction above Dissolving a Solute When mixing a solute with the solvent attractions between the like substances must break while attractions between solute solvent are formed If the new solute solvent attractions are strong enough the solute will dissolve Water is a polar molecule with uneven distribution of electrons more on the oxygen less on the hydrogen When ionic compounds dissolve in water each ion is attracted to the polar water and surrounded by a solvent cage of water The result is a solution with free moving charged particles that may conduct electricity Materials that dissolve in water to form a solution that will conduct electricity are called electrolytes Chapter 4 Chemistry 1A Page 7 Electrolytes in Aqueous Solution Strong Electrolytes will largely dissociate into its ions in an aqueous solution and are written as separated ions in the ionic reactions Examples Strong acids Strong Bases Soluble salts Strong Acids HCl HBr HI HNO3 H2SO4 HClO4 HClO3 Strong Bases soluble hydroxides from Group 1A not including H and Group 11A not including the top two LiOH NaOH KOH RbOH Ca OH 2 Sr OH 2 Ba OH 2 Soluble Salts Ionic compounds that contain the cations from Group 1A Li Na K Rb Cs or ammonium ion NH4 A compound is probably soluble if it has the anion Cl 1 Br 1 I 1 except with Ag Hg2 2 or Pb 2 and most compounds that include NO3 1 ClO4 1 C2H3O2 1 Soluble with most SO4 2 except Ba 2 Hg2 2 or Pb 2 Weak Electrolytes will partially dissociate into its ions in an aqueous solution but are written as compounds in an ionic equation Weak electrolytes are the weak acids and weak bases such as HC2H3O2 or NH3 Nonelectrolytes will stay in their