M03 - Stoichiometry PDF

9/8/2024...

9/8/2024 Chapter Outline (3.1) The mole (3.2) Mass relations in chemical formulas (3.3) Mass relations in reactions Chapter 3 Mass Relations in Chemistry; Stoichiometry Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1 2 Masses of Atoms in Grams Avogadro’s Number It is necessary to know the mass of an atom in grams so the quantity of Corresponds to a collection of atoms where the mass of that collection in matter can be determined by weighing grams is numerically equal to the same number in a mu, for a single atom One He atom is about four times as heavy as one H atom NA = 6.022  1023 The mass of 100 He atoms is about four times the mass of 100 H atoms Number of atoms of an element in a sample whose mass is numerically equal The number of H e atoms in 4.003 g helium = The number of H atoms in 1.008 g of to the mass of a single atom hydrogen By knowing Avogadro’s number and the atomic mass, it is now possible to Avogadro’s Number (NA): Number of atoms of an element in a sample calculate the mass of a single atom in grams whose mass in grams is numerically equal to the atomic mass of the element NA = 6.022  1023 Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 3 4 The Mole Significance of the Mole A mole is Avogadro’s number of items By knowing Avogadro’s number and the atomic mass, it is now possible to 1 𝑚𝑜𝑙 = 6.022 × 1023 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 calculate the mass of a single atom in grams Mole is a very large number mass = MM  n Avogadro’s number of pennies is enough to pay all the expenses of the United States for a billion years or more, without accounting for inflation MM is the molar mass (g/mol) Molar mass n is the amount in moles Numerically equal to the sum of the masses (in a m u) of the atoms in the formula Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 5 6 1  9/8/2024 Example Ans: 𝟏. 𝟔𝟔 × 𝟏𝟎−𝟐𝟒 mol; 𝟏. 𝟐𝟒 × 𝟏𝟎−𝟐𝟐 g Example Given: 1 As atom; Required: mol As, g As From Periodic Table, AMAs=74.922 g/mol Consider arsenic (As), a favourite poison used in crime stories. Determine the moles and mass of an arsenic atom. Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 7 8 Example Ans: 𝟑. 𝟎𝟕 × 𝟏𝟎𝟐𝟑 molecules; 91.62 g Example Given 0.509 mol ASA, C9H8O4; Required: g ASA, molecules ASA From Periodic Table, AMC=12 g/mol; AMO=16 g/mol; AMH=1 g/mol; AMASA=180 g/mol Acetylsalicylic acid (A SA), C9H8O4, is the active ingredient of aspirin. What is the mass in grams and number of molecules of 0.509 moles of A SA? Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 9 10 Figure 3.3 - Flowchart for the Interconversion of Solute Concentrations - Molarity Particles, Mass, and Moles Molarity Molarity - moles of solute/liters of solution Symbol is M Square brackets are used to indicate concentration in M Na +  = 1.0 M Consider a solution prepared from 1.20 mol of substance A, diluted to a total volume of 2.50 L Concentration is 1.20 mol/2.50 L or 0.480 M Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 11 12 2  9/8/2024 Molarity Figure 3.4 - Preparing One Liter of 0.100 M Potassium Chromate Used to calculate Number of moles of solute in a given volume of solution Volume of solution containing a given number of moles of solute Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 13 14 Example Ans: 0.45 mol HNO3; 28.35 g HNO3; 𝟐. 𝟎𝟑𝟕 × 𝟏𝟎𝟐𝟒 molecules H2O Example Given: 75 mL, 6 M HNO3, ρ (solution) = 1.19 g/mL; Required: mol HNO3, g HNO3, molecules H2O Nitric acid, HNO3, is extensively used in the manufacture of fertilizer. A bottle From Periodic Table, AMN=14 g/mol; AMO=16 g/mol; AMH=1 g/mol; AMHNO3=63 g/mol containing 75.0 mL of nitric acid solution is labeled 6.0 M H NO3. How many moles and grams of HNO3 are in the bottle? How many molecules of water does it contain? Density of solution is 1.19 g/mL Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 15 16 Dissolving Ionic Solids Determining Moles of Ions When an ionic solid is dissolved in a solvent, the ions separate from each By knowing the charge on ions, the formula of a compound can be quickly other determined 2+ − Formula of the compound is key to determining the concentration of ions in MgCl2 (s) → Mg (aq) + 2Cl (aq) solution Concentrations of ions are related to each other by the formula of the compound Molarity of Mg2+ = Molarity MgCl2 Molarity of Cl− = 2  molarity of MgCl2 Total number of moles of ions per mole of M gCl2 is 3 Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 17 18 3  9/8/2024 Example Ans: 0.29 M K+; 0.145 M Cr2O72-; 𝟐. 𝟏𝟖𝟑 × 𝟏𝟎𝟐𝟐 ions K+; 𝟏. 𝟎𝟗𝟏 × 𝟏𝟎𝟐𝟐 ions Cr2O72- Example 2.3 (a) (1 of 5) Given: 125 mL, 0.145 M K2Cr2O7; Required: [K+], [Cr2O72-], ions of K+ & Cr2O72- Potassium dichromate, K2Cr2O7, is used in the tanning of leather. A flask From Periodic Table, AMK=39 g/mol; AMO=16 g/mol; AMCr=52 g/mol; AMK2Cr2O7=294 g/mol containing 125 mL of solution is labeled 0.145 M K2Cr2O7. What is the molarity of each ion in solution? How many particles of each ions are present? Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 19 20 Mass Relations in Chemical Formulas Chemical Analysis Percent composition from formula Experimentation can give data that lead to the determination of the formula of Percent composition of a compound is stated to be the number of grams of each a compound element in 100 g of the compound Masses of elements in the compound By knowing the formula, the mass percent of each element can be readily Mass percents of elements in the compound calculated Masses of products obtained from the reaction of a weighed sample of the compound Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 21 22 Simplest Formula from Chemical Analysis Figure 3.5 - Flowchart for Determining the Simplest Formula of a Compound Often, the formula is not known, but data from chemical analysis is known Amount of each element in grams Used to determine the empirical formula Simplest formula in a compound Smallest whole-number ratio of atoms in a compound H2O is the empirical formula and the molecular formula for water HO is the empirical formula for hydrogen peroxide; the molecular formula is H2O2 Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 23 24 4  9/8/2024 Molecular Formula from Simplest Formula Simplest Formula from Mass Percents Relationship between the empirical and molecular formula is a whole number When dealing with percentages, assume 100 g of the compound Whole number relates the molecular mass to the mass of the empirical By doing so, the unitless percentage becomes a meaningful mass formula as well Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 25 26 Example Ans: 46.67% Si, 53.33% O Example Given: SiO2 Silicon dioxide is a common impurity in ores. Determine the mass % of each Required: %Si, %O for SiO2 Using Basis: 1 mol SiO2 element in the said compound. From Periodic Table, AMSi=28 g/mol; AMO=16 g/mol; AMSiO2=60 g/mol A 30.00 g sample of a white crystal used in water purification contains 4.734 g of aluminum, 8.436 g of sulfur, and 16.83 g of oxygen. Find the empirical formula of the compound. Vitamin C is found in many fruits and vegetables, particularly in citrus fruit. Its simplest formula is C3H4O3 and its molar mass (determined by a mass spectrometer) is 176 g/mol. What is the molecular formula of citric acid? Metallic iron is most often extracted from hematite ore. Hematite ore has a compound of iron mixed with impurities. The iron compound has a molar mass of 159.69 g/mol and contains 69.94% iron while the rest are oxygen. What is the name of the iron compound? Determine how many grams of each element are present in 30 g SF 6. Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 27 28 Example Ans: Al2S3O12 Example Ans: C6H8O6 Given: 30 g crystal, 4.734 g Al, 8.436 g S, 16.83 g O; Given: C3H4O3, MM=176 g/mol; Required: empirical formula Required: molecular formula of citric acid From Periodic Table, AMAl=26.982 g/mol; AMS=32 g/mol; AMO=16 g/mol Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 29 30 5  9/8/2024 Example Ans: Iron (III) oxide Example Ans: 6.58 g S, 23.42 g F Given: Iron compound with 69.94% Fe, rest are O, MM=159.69 g/mol; Given: 30 g SF6 Required: name of iron compound Required: g S, g F %O = 100 - %Fe = 100 – 69.94 = 30.06%O From Periodic Table, AMS=32 g/mol; AMF=19 g/mol; AMSF6=146 g/mol Basis: 100 g compound From Periodic Table, AMFe=55.845 g/mol; AMO=16 g/mol Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 31 32 Mass Relations in Reactions Writing Equations Chemical equations represent chemical reactions One must know the reactants and the products of a reaction for which an Reactants appear on the left equation is to be written Products appear on the right Often necessary to do an experiment and an analysis to determine the products of a reaction Equation must be balanced Determining the products is often time consuming and difficult Number of atoms of each element on the left equals the number of atoms of each element on the right Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 33 34 Writing Chemical Equations Mass Relations from Equations Write a skeleton equation for the reaction Coefficients of a balanced equation represent the numbers of moles of reactants and products Indicate the physical state of each reactant and product 2𝐴 + 𝐵 → 3𝐶 + 4𝐷 Balance the equation 2 mol A + 1 mol B → 3 mol C + 4 mol D Only the coefficients can be changed; subscripts are fixed by the chemical nature of the reactants and products It is best to balance atoms that appear only once on each side of the equation first Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 35 36 6  9/8/2024 Figure 3.11 - Flowchart for Mole-Mass Example Conversions Crystals of sodium hydroxide react with carbon dioxide from air to form a colorless liquid, water, and a white powder, sodium carbonate, which is commonly added to detergents as a softening agent. Write a balanced equation for this chemical reaction. Ammonia is used to make fertilizers (Figure 3.12) for lawns and gardens by reacting nitrogen gas with hydrogen gas. The balanced equation for the reaction is N2(g) + H2(g) → NH3(g). How many moles of ammonia are formed when 1.34 mol of nitrogen reacts with a stoichiometric amount of hydrogen? Liquid hydrazine (N2H4) is a rocket propellant fuel. It reacts with liquid NTO (dinitrogen tetroxide) to produce nitrogen gas and water vapor. Given that the rocket releases 200 g of nitrogen per minute, determine the mass (kg) of the reactants needed to sustain the rocket in a 12-hour flight to orbit. Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 37 38 Example Ans: 𝟐𝑵𝒂𝑶𝑯(𝒔) + 𝑪𝑶𝟐(𝒈) → 𝑯𝟐𝑶(𝒍) + 𝑵𝒂𝟐𝑪𝑶𝟑(𝒔) Example Ans: 2.68 mol NH3 Crystals of sodium hydroxide react with carbon dioxide from air to form a colorless liquid, water, and Given: 1.34 mol N2; N2(g) + H2(g) → NH3(g) a white powder, sodium carbonate, which is commonly added to detergents as a softening agent. Required: mol NH3(g) formed Write a balanced equation for this chemical reaction. Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 39 40 Example Ans: 82.29 kg hydrazine, 236.57 kg NTO Liquid hydrazine (N2H4) is a rocket propellant fuel. It reacts with liquid NTO (dinitrogen tetroxide) to Limiting Reactant and Theoretical Yield produce nitrogen gas and water vapor. Given that the rocket releases 200 g of nitrogen per minute, determine the mass (kg) of the reactants needed to sustain the rocket in a 12-hour flight to orbit. From Periodic Table, MMN2H4=32 g/mol; MMN2O4=92 g/mol; AMN2=28 g/mol; AMH2O=18 g/mol Reaction of Antimony with Iodine Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 41 42 7  9/8/2024 Approach to Limiting Reactant Problems Experimental Yield Calculate the amount of product that will form if the first reactant were Quantity of product measured after performing the reaction in the laboratory completely consumed Experimental yields are always lower than theoretical yields Repeat the calculation for the second reactant in the same way Some of the product is lost to competing reactions Choose the smaller amount of product and relate it to the reactant that Some of the product is lost to handling produced it Some of the product may be lost in separating it from the reaction mixture This is the limiting reactant, and the resulting amount of product is the theoretical yield From the theoretical yield, determine how much of the reactant in excess is used, and subtract from the starting amount Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 43 44 Percent Yield Example Consider the reaction 3Sb(s) + 2I2(s) → 3SbI3(s), (a) if 1.20 mol Sb and 2.40 mol I2 were mixed, what is the limiting reactant, excess reactant, Defined as theoretical yield, and the moles of excess reactants left after the reaction? (b) 100 g Sb and 100 g I2 were mixed, what is the limiting reactant, excess reactant, theoretical yield, and the mass of excess reactants left after the reaction? experimental yield Consider the reaction between magnesium and iodine to produce magnesium percent yield =  100% theoretical yield iodide. A student determines by calculation that with the amount of reagents he has on hand, he should produce 1.71 mol of MgI2. After the reaction is complete, he tells his TA that he got a yield of 84.5%. How many grams of M gI2 did he make? Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 45 46 Example Ans: I2 is excess, Sb is limiting, 1.2 mol SbI 3, 0.6 mol excess I2 Example Ans: I2 is limiting, Sb is excess, 131.98 g SbI 3, 68.02 g excess Sb Given: 3Sb(s) + 2I2(s) → 3SbI3(s) [check the equation!], (a) 1.20 mol Sb & 2.40 mol I2, Given: 2Sb(s) + 3I2(s) → 2SbI3(s), (b) 100 g Sb & 100 g I2 Required: limiting & excess reactants, theoretical yield, amount of excess in moles Required: limiting & excess reactants, theoretical yield, amount of excess in mass From Periodic Table, MMSb=121.76 g/mol; MMI2=253.8 g/mol; AMSbI3=502.46 g/mol Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 47 48 8  9/8/2024 Example Ans: 401.84 g MgI2 Given: 1.71 mol theoretical MgI2, 84.5% yield Key Concepts (1 of 2) Required: g of actual MgI2 From Periodic Table, MMMg=24.3 g/mol; MMI2=253.8 g/mol; AMMgI2=278.1 g/mol Use molar mass to relate Moles to mass Moles in solution; molarity Molecular formula to simplest formula Use the formula of a compound to find percent composition or its equivalent Find the simplest formula from chemical analysis data Balance chemical equations by inspection Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 49 50 Key Concepts (2 of 2) Use a balanced equation to Relate masses of products and reactants Find the limiting reactant, theoretical yield, and percent yield Masterton/Hurley, Chemistry: Principles and Reactions, 8th Edition. © 2016 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 51 9