STOICHIOMETRY: Part I Jessa Loraine M. Ramos, RChE Special Science Teacher I PRAYER “I will continue, O my God, to do all my actions for the love of you.” Attendance Check QUIZ! Chemical nomenclature and formula writing Stoichiometry “chemical stoichiometry” – area of study which deals with the quantities of materials consumed and produced in chemical reactions. Contents of the Lesson 01 03 Atomic Mass Review relative atomic mass Percent Composition Calculations for percent composition of compounds 02 04 The Mole and Molar Mass Avogadro’s Number, molar mass calculations and mass to mole conversion and vice versa Empirical and Molecular Formulas Describe the topic of the section here 01 Atomic Mass Review relative atomic mass of elements Mass Spectrometer Review Problem- Atomic weight Potassium, a metal that is highly reactive in water, has three isotopes, K-39, K-40, and K-41. Given the atomic masses and abundances of the three isotopes, calculate the average atomic mass of potassium. ISOTOPE ATOMIC MASS % ABUNDANCE K-39 38.9637 amu 93.26% K-40 39.9640 amu 0.01% K-41 40.9618 amu 6.73% Got questions? 02 The Mole and Molar Mass Avogadro’s Number, molar mass calculations and mass-to-mole conversions and vice versa Mole mol, SI system base unit for the amount of substance One mole of something consists of 6.022 x 1023 units of that substance For Atoms 1 mol Ar = 6.022 x 1023 Ar atoms For molecules 1 mol H2O = 6.022 x 1023 H2O molecules For ions 1 mol Na+ = 6.022 x 1023 Na+ ions For ionic compounds 1 mol NaCl = 6.022 x 1023 NaCl formula units For other particles 1 mol e- = 6.022 x 1023 e- particles One mole of something consists of 6.022 x 1023 units of that substance Determining Moles of Atoms Sample Problem 1: Aluminum (Al) is a metal with high strength-to-mass ratio and a high resistance to corrosion; thus it is often used for structural purposes. Compute the number of atoms in a sample containing 0.371 mol of Aluminum atoms. Determining Moles of Atoms SOL’N: Got questions? Counting Atoms Counting Atoms Molar Mass ๏ผ ๏ผ The mass that an atom, or any substance, has in 1 mole Measured in gram per mole (g/mol) Molar Mass The unit for the molar mass is gram per mole (g/mol). Its value is the same as the value of the atomic mass in amu. Molar Mass For substances consisting of more than one atom, the molar mass is the sum of all the molar masses of all atoms present. Molar Mass Calculations Sample Problem 2: Calculate the molar mass of elemental nitrogen, N2 SOL’N: MMN2 = 2 x 14.01 g/mol ๐๐๐๐ = 28.02 g/mol Got questions? YOUR TURN! Molar Mass Calculations Sample Problem 3: Calculate the molar mass of sodium bicarbonate. Ans: 84.01 g/mol Molar Mass Calculations Sample Problem 4: Calculate the molar mass of Ca3(PO4)2. Ans: 310.18 g/mol Mass to mole conversion and vice versa Got questions? ๐ง RECALL Unit conversions and use of conversion factors or unit factors ๐ง RECALL Mass to mole calculations, vice versa ๏ถ The molar mass shows the relationship between the mass and the number of moles in a substance. ๏ถ The molar mass can serve as the unit factor for converting the mass to the number of moles or vice versa. Sample Problem 5 ๏ถ What is the mass, in grams, of 0.0245 mol of Uranium, U? Sample Problem 6 ๏ถ How many grams are there in a 2.18-mol sample of KCl? Sample Problem 6 Mass to mole calculations, vice versa Got questions? YOUR TURN! Exercises ๏ถ ๏ถ How many moles are there in 21.47 g of Zn? How many moles are there in 3.18 g of AlCl3? Sample Problem 7 Sample Problem 8 ๏ถ What is the mass of 7.645 x 1021 CaBr2 formula units? Sample Problem 8 Sample Problem 9 Mass to mole calculations, vice versa Got questions? YOUR TURN! Marathon Problems ๏ถ ๏ถ Compute the number of moles and atoms in a sample containing 7.00 g of K. Compute for the number of moles and mass of 2.23x1023 atoms of Al. Marathon Problems! ๐ง ๏ถ What is the (a) mass of 1 mol of ammonia in grams? (b) How many molecules are present in 1 mol of ammonia? ๏ถ Ans. A) 17.04 g, B) 6.022x1023 molecules Marathon Problems! ๐ง ๏ถ Cobalt (Co) is a metal that is added to steel to improve its resistance to corrosion. Calculate both the number of moles in a sample of cobalt containing 5.00 x 1020 atoms and the mass of the sample. ๏ถ Ans. 8.30x10-4 mol Co, 4.89x10-2 g Co 03 Percent Composition Calculations for percent composition of compounds Percent Composition ๐๐๐ ๐ ๐๐ ๐ ๐๐ 1 ๐๐๐ ๐๐ ๐๐๐๐๐๐ข๐๐ %๐ = ๐ฅ100% ๐๐๐ ๐ ๐๐ 1 ๐๐๐ ๐๐ ๐กโ๐ ๐๐๐๐๐๐ข๐๐ Example 1 Example 1 Example 2 Example 2 Got questions? YOUR TURN! Problem 1 Exercises 1. Determine the percent composition of each element in CH4Cl3F 2. Calculate the mass percent composition of every element in CO2 Got questions? Empirical Formula ๏ผ the simplest, whole-number ratio of atoms in a molecule ๏ผ can be determined from percent composition or combining masses ๏ผ Example: CH2O is the empirical formula of C6H12O6 (glucose) Sample Problem 10 ๏ถ Cyclohexene is made up of 87.73% C and 12.27% H. Determine the empirical mass of cyclohexene. Sample Problem 10 Sample Problem 10 Sample Problem 10 Sample Problem 11 ๏ถ A nitrogen oxide molecule consists of 25.9% N and 74.1% O. What is the empirical formula for this compound? Sample Problem 11 Sample Problem 11 Sample Problem 11 Got questions? YOUR TURN! Exercises 1. A sample contains 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the empirical formula of the compound? 2. Nutrasweet is 57% C, 6.16% H, 9.52%N, and 27.18% O. Find the empirical formula of Nutrasweet. Molecular Formula ๏ผ a multiple of the empirical formula; the chemical formula that gives the actual number of atoms of every element in a compound ๏ผ Example: C6H6 is the molecular formula of Benzene Sample Problem 12 ๏ถ A compound with empirical formula CH is found to have a molecular mass of 104.14 g/mol. Determine the molecular formula of the compound. Sample Problem 12 Sample Problem 12 Sample Problem 12 Sample Problem 13 ๏ถ A solid has empirical formula N2O5. An experiment was done to determine its molar mass, and a value of 108.7 g/mol was obtained. What is the molecular formula of the solid? Sample Problem 13 Sample Problem 13 Sample Problem 13 YOUR TURN! Exercises 1. Determine the empirical and molecular formulas for a compound that gives the following percentages on analysis (in mass percents): 71.65% Cl 24.27%C 4.07% H The molar mass is known to be 98.96 g/mol. Exercises 2. A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. The compound has a molar mass of 283.88 g/mol. What are the compound’s empirical and molecular formulas? Got questions? “ ” Thanks! Do you have any questions? jessaLoraine.ramos@deped.gov.ph Jessa Loraine M. Ramos Stay safe and God bless, everyone! Please keep this slide for attribution CREDITS: This presentation template was created by Slidesgo, including icons by Flaticon, and infographics & images by Freepik