Transcript CHAPTER 4
CHAPTER 4 Stoichiometry Calculations Based on Chemical Equations Fe2O3 + 3 CO 2 Fe + 3 CO2 How many CO molecules are required to react with 25 molecules of Fe2O3? 2 Calculations Based on Chemical Equations What mass of CO is required to react with 146 g of iron (III) oxide? Fe2O3 + 3 CO 2 Fe + 3 CO2 3 Calculations Based on Chemical Equations What mass of carbon dioxide can be produced by the reaction of 0.540 mole of iron (III) oxide with carbon monoxide? Fe2 O3 + 3 CO 2 Fe + 3 CO2 4 Calculations Based on Chemical Equations How many iron atoms can be produced by the reaction of 2.50 x 105 molecules of iron (III) oxide with excess carbon monoxide? Fe2O3 + 3 CO 2 Fe + 3 CO2 5 Calculations Based on Chemical Equations What mass of iron (III) oxide reacted with carbon monoxide if the carbon dioxide produced by the reaction had a mass of 8.65 grams? Fe2O3 + 3 CO 2 Fe + 3 CO2 You do it! 6 Limiting Reactant Concept The reagent consumed first is the limiting reactant (or limited reagent) – -A chemical reaction proceeds forward according to the stoichiometry of the reaction until one (or both) reactants are consumed 7 Limiting Reactant Concept • Kitchen example of limiting reactant concept: 1 packet of muffin mix + 2 eggs + 1 cup of milk makes 12 muffins 8 Limiting Reactant Concept 1 packet of muffin mix + 2 eggs + 1 cup of milk 12 muffins • Mix Packets 1 2 3 4 5 6 7 Eggs Milk 1 dozen 1 gallon limited by the muffin mix 1 dozen 1 gallon 1 dozen 1 gallon 1 dozen 1 gallon 1 dozen 1 gallon 1 dozen 1 gallon 1 dozen 1 gallon limited by the amount of eggs 9 Limiting Reactant Concept Suppose a box contains 87 bolts, 110 washers, and 99 nuts. How many sets, each consisting of one bolt, two washers, and one nut, can you construct from the contents of one box? 10 Limiting Reactant Concept How much sulfur dioxide can be produced by the reaction of 95.6 g of carbon disulfide with 1.10 x102 g of oxygen? CS2 3 O2 CO 2 2 SO 2 1 mol 3 mol 1 mol 2 mol • Which is limiting reactant? • What is maximum mass of sulfur dioxide that can be produced? 11 Percent Yield Theoretical yield is calculated by assuming that the reaction goes to completion – -Determined from a limiting reactant calculation Actual yield is the amount of a specified pure product made from the reactants – -In the laboratory, this is the amount of product that is formed in your beaker, after it is purified and dried Percent yield indicates how much of the product is obtained from the reaction actual yield % yield = 100% theoretical yield 12 Percent Yield A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 14.8 g of ethyl acetate, CH3COOC2H5. What is the percent yield? CH 3COOH + C2 H 5OH CH 3COOC2 H 5 H 2O 1. Calculate the theoretical yield • 2. Calculate the percent yield 13 Types of Solutions 14 Concentrations of Solutions • Common unit of concentration: g solute number of molesof solut e MW solute molarit y = number of lit ersof solut ion liters solution moles M L 15 Solution Preparation Making a 1 M solution of sodium chloride Then add addition water until the 1.0 L mark is reached 16 Concentrations of Solutions • Calculate the molarity of a solution that contains 12.5 g of sulfuric acid in 1.75 L of solution. 17 Concentrations of Solutions • Determine the mass of calcium nitrate required to prepare 3.50 L of 0.800 M Ca(NO3)2 . You do it! 18 Diluting a Solution A known amount of solvent is added to a known concentration and known amount of solution • -number of moles of solute in the two solutions (concentrated and dilute) remains constant • -mathematical relationship: • M1V1 = M2V2 • -Note: appropriate for dilutions, but not for chemical reactions 19 Diluting a Solution • If 10.0 mL of 12.0 M HCl is added to enough water to give 100. mL of solution, what is the concentration of the solution? 20 Diluting a Solution • What volume of 18.0 M sulfuric acid is required to make 2.50 L of a 2.40 M sulfuric acid solution? 21 Solutions in Chemical Reactions • -chemical reactions are most often performed by using solutions of the reactants • -Combine the concepts of molarity and stoichiometry 22 Solutions in Chemical Reactions • What volume of 0.500 M BaCl2 is required to completely react with 4.32 g of Na2SO4? Na 2SO 4 + BaCl2 BaSO 4 + 2 NaCl 23 Solutions in Chemical Reactions • What volume of 0.200 M NaOH will react with 50.0 mL 0f 0.200 M aluminum nitrate, Al(NO3)3? AlNO3 3 3 NaOH AlOH3 3 NaNO3 You do it! 24 Titrations A method of determining the concentration of an unknown solution by reacting it with a known amount and concentration of a standard solution Standard solution: solution whose concentration has been determined using a primary standard by standardization Primary standard: chemical compound which can be used to accurately determine the concentration of another solution Examples: include KHP and sodium carbonate 25 Primary Standard • Potassium hydrogen phthalate (KHP) – molar mass of 204.2 g/mol. O CH HC O CH C C OH + HC C CH O C C HC C O -K+ HC C O KOH CH OH + H2O C OH acidic H KHP 26 Titrations Standardization: process in which the concentration of the standard solution is determined from the primary standard Indicator: substance that exists in different forms with different colors depending on the concentration of the H+ in solution Examples: phenolphthalein and bromothymol blue. Equivalence point: point at which stoichiometrically equivalent amounts of the acid (H+) and base (OH-) have reacted End point: point at which the indicator changes color27 and the titration is complete Titration • Calculate the molarity of a NaOH solution if 27.3 mL of it reacts with 0.4084 g of KHP. NaOH + KHP NaKP + H 2 O 1 mol KHP ? mol+NaOH = 0.4084 g KHP KHP 1 mol KHP(aq) NaOH(aq) NaKP(aq) + ? mol NaOH = 0.4084 g KHP 204.2g KHP H2O(l) 204.2 g KHP 1 mol NaOH 0.00200 mol NaOH 1 mol NaOH 1 mol KHP 0.00200 mol NaOH 1 mol 0.00200 mol KHP NaOH ? M NaOH = 0.0733 M NaOH 0.0273 L NaOH 28 Titrations • What is the molarity of a KOH solution if 38.7 mL of the KOH solution is required to react with 43.2 mL of 0.223 M HCl? KOH(aq) + HCl(aq) H2O(l) + KCl(aq) 29 Titrations • What is the molarity of a barium hydroxide solution if 44.1 mL of 0.103 M HCl is required to react with 38.3 mL of the Ba(OH)2 solution? Ba(OH)2 + 2 HCl BaCl2 + 2 H2O 30 Titrations On Your Own • Calculate the molarity of a sulfuric acid solution if 23.2 mL of it reacts with 0.212 g of Na2CO3. H2SO4(aq) + Na2CO3(aq) Na2SO4(aq) + H2O(l) + CO2(g) 31 Transmittance and Absorption Spectrum Transmittance (T): ratio of the amount of light that passes through a sample relative to the initial amount of light entering the sample Absorbance (A) = -log T = -log (P/Po) Beer-Lambert Law (Beer’s Law): A = ebc 32