Unit Outline • Introduction : Measures of Quantity • Molar Mass • Molar Volume • Percent Composition • Finding Formulas
Measures of Quantity 1 dozen = 12 doughnuts EX1 : How many doughnuts are in 4.0 dozen? EX2 : How many dozen are in 27 doughnuts?
Measures of Quantity 1 mole = 6.02 x 1023 particles EX1 : How many atoms are in 3.00 moles of sulfur? EX2 : How many moles are in 5.0 x 1024 atoms of Na?
Representative Particles • Atoms • Ions • Formula Units • Used for ionic compounds • Molecules • Used for covalent compounds
Moles and the Periodic Table The atomic mass on the periodic table tells us how much one mole of the element weighs. The mass in grams of one mole of a substance Molar Mass:
Molar Mass Examples 63.5 g/mol • What is the mass of 1 mole (6.02 x 1023 atoms) of Cu? 63.5 g • What is the molar mass of Cu? • What is the molar mass of Cl? 35.5 g/mol • What is the mass of 1 mole (6.02 x 1023 atoms) of Cl? 35.5 g 71.0 g • Find the mass of 2 moles of Cl. • What is the molar mass of CuCl2? 134.5 g/mol • Find the mass of 1 mole of CuCl2. 134.5 g • Find the mass of 2 moles of CuCl2. 269.0 g
More Molar Mass Examples • What is the mass of 0.60 mol Li2SO4? • How many moles of Mg(OH)2 are there in 24.3 g of Mg(OH)2?
Hints for Multi-Step Conversions • KEY #1 : Set up a roadmap. (airport example) • KEY #2 : Always start with what you are given. • KEY #3 : Always convert to moles first. • KEY #4 : Always include the units in your calculation. • KEY #5 : BE CAREFUL!
Multi-Step Conversion Practice EX1 : How many molecules are in 6.3g of HBr? Roadmap : molecules HBr grams HBr
Multi-Step Conversion Practice EX1 : How many molecules are in 6.3g of HBr? Roadmap : molecules HBr grams HBr moles HBr Solution :
Multi-Step Conversion Practice EX2 : How many grams of carbon are in 4.36 x 1024 atoms of carbon? Roadmap : atoms C moles C grams C Solution :
Multi-Step Conversion Practice EX3 : How many grams of magnesium sulfide are in 0.32 moles of magnesium sulfide? Roadmap : moles MgS grams MgS Solution :
Moles and Volume 0 Celcius & 1 atm Standard Temperature & Pressure One mole of any gas at STP has a volume of 22.4 Liters.
Moles and Volume 0 Celcius & 1 atm Standard Temperature & Pressure Aha sound One mole of any gas at STP has a volume of 22.4 Liters. 22.4 Liters is often called the Molar Volume
This works for any gas. • But gases have different masses right? How can they have the same volume? • Remember the Auditorium analogy.
Molar Volume Examples • 3.4 moles of O2 occupies how much volume? • A gas occupies 240 L. How many moles of the gas are there?
Multi-Step Conversion Practice II EX1 : How many grams of carbon monoxide are in 26.8 L of carbon monoxide at STP? Roadmap : Liters CO moles CO grams CO Solution :
Multi-Step Conversion Practice II EX2 : How many Liters of methane (CH4) are in 3.35 x 1032 molecules of methane at STP? Roadmap : molecules moles Liters Solution :
Percent Composition Percent composition tells us the mass of each element in the compound relative to the total mass of the compound.
Percent Composition Example 1 • EX1 : Find the percent composition of all the elements in H2O. 2 x 1.0 = 11.1% = 88.9%
Percent Composition Example 2 • EX2 : Find the percent composition of all the elements in Ca(MnO4)2. = 14.4% = 39.5% = 46.1%
Molecular and Empirical Formulas Empirical Formula – The lowest whole number ratio of the elements in a compound. EX1 : CH2O EX2 : NO3 Molecular Formula – The actual ratio of the elements in a compound as found in nature. EX1 : C6H12O6 EX2 : N2O6
Steps to Solving Empirical Formula Problems When finding formulas, you may have to assume a 100g sample. • Step 1: Percent Grams • Step 2: Grams Moles • Step 3: Divide by smallest moles • Step 4: Multiply by integer if necessary
Empirical Formula Example 1 EX1 : A compound is found to be 27.1% Na, 16.5% N, and 56.4% O. What is the empirical formula of the compound?
Empirical Formula Example 2 Example 2: A compound is analyzed and found to contain 25.8% N and 74.2% O. What is the empirical formula of the compound?
Finding Molecular Formulas • In order to find the molecular formula, you must have the following pieces of information: • The empirical formula • The molar mass of the molecule as found in nature.
EX1: Finding Molecular Formulas EX1 : The empirical formula is HO. The molar mass of the compound is 34.0 g/mol. What is the molecular formula? 2 2 (HO)
EX2 : Finding Molecular Formulas A compound has a molar mass of 150.0 g/mol. This compound has a chemical composition of 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen. Find the molecular formula of the compound. 40.0% C --> 40.0 g C 3.33 mol C 1 6.67% H --> 6.67 g H 6.67 mol H 2 53.3% O --> 53.3 g O 3.33 mol O 1 EMPIRICAL FORMULA : CH2O
EX2 : Finding Molecular Formulas A compound has a molar mass of 150 g/mol. This compound has a chemical composition of 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen. Find the molecular formula of the compound. EMPIRICAL FORMULA : CH2O MOLECULAR FORMULA : C5H10O5