** Refer to atomic mass on Periodic Table!!! ** Review *** a.) 1 a.m.u. = 1/12 the mass of a ____________ atom b.) subscript = # of ____________. Eg. How many total atoms in calcium nitrate? MOLES * In Chemistry, we count using moles.* • 1 Mole = 6 x 1023 atoms (particles). • (1 mole = # of atoms present in 12g of C-12) Mole vs. Dozen • To understand “moles” better, we should compare 1 mole and 1 dozen. • Q.1. How many apples are in 1 dozen? • Q.2. How many atoms are in 1 mole? • Q.3. Which has a greater mass, 1 dozen apples or 1 dozen grapes? • Q.4. Which has a greater mass, 1 mole of sodium atoms or 1 mole of mercury atoms? Many names, same concept! Mass of 1 Mole = • “gram atomic mass”, • “gram formula mass”, • “molar mass”, • “formula weight”, • “gram molecular mass”. Practice – Use Periodic Table • Eg. 1.) 1 atom of H = 1 a.m.u. 1 mole of H = 1g. 2.) 1 atom of C = 12 a.m.u. 1 mole of C = 12g. 3.) 1 atom of Mg = _____________ 1 mole of Mg = _____________ 4.) 2 atoms of Mg (or, “Mg2”) = _______________ 2 moles of Mg = ___________ 5.) 1 molecule of CO2 = ____________ 1 mole of CO2 = ______________ Atomic Mass • Atomic mass – The sum total mass of all present atoms (in a.m.u.) ** Always give your answer as specific as the question suggests. ** Atomic Mass Eg. Give the atomic mass for all of the following to the nearest tenth . . . 1.) KCl 2.) Ca3N2 3.) (NH4)2S 4.) CCl4 Gram formula mass • Gram formula mass (gfm) (a.k.a. “molecular mass” or “formula mass”) • the sum total mass using grams (g) instead of a.m.u. • (gfm) always equals 1 mole (mol) of a compound **(gfm = 1 mole) *** Q.1. How many molecules are in 1 mole? Practice Eg. Give a.)the total # of atoms and b.)the gram formula mass (gfm) for each of the following (round to whole #) 1.) NaCl 2.) F2 3.) K2CO3 4.) Al(OH)3 5.) C6H12O6 Hydrates • Hydrates: – Ionic compound with water (H2O) attached. – Hydrate = crystals that contain water molecules. – Anhydrous = substance without water molecules. Hydrates Q.1 What is the mass of 1 mole of H2O (the gfm of H2O)? Q.2 What is the gram formula mass (gfm) of 5 H2O? Hydrates • Give the gram formula mass (gfm) for each of the following Hydrates: 1.) CuSO4 ∙ 5H2O 2.) NiSO4 ∙ 6H2O 3.) MgCl2 ∙ 2H2O “ ∙ ” = “+” Mole-Mass Conversions Total mass (g) = (# of Moles) x (gfm) Eg.1 What is the mass of 3 moles of H2SO4? Total mass = (3 mol)(gfm of H2SO4) =_____________ Eg.2 What is mass of .5 moles of copper(II) sulfate? Eg.1 How many moles are there in 88g of CO2? Step 1: find the gfm of CO2 Step 2: solve the equation Eg.2 How many moles are there in 72g of CH4 Practice Problems • 1.) What is the mass of 2 moles of iron(II) nitrite? • 2.) How many moles are in 46g H2SO4? • 3.) What is the mass of 0.5 mol carbon dioxide? • 4.) How many moles are in 544g CaSO4? % Composition 1.) What is the % composition of oxygen in H2O? 2.) What is the % composition of hydrogen in H2O? % Composition • % Composition = mass _ of _ part x100% Total _ mass Eg.1 What is the % composition of Carbon in CO2? Step 1: get the gfm of C (“part”) Step 2: get the gfm of CO2 (“total”) Step 3: plug into equation and solve. • Eg.2 Find the % composition of C, H, and O in C6H12O6. • Eg.3 What is the % composition of water in CuSO4 ∙ 5H2O? • Eg.4 What is the % water in NiSO4 ∙ 6H2O? What is the % Ni? The Element Song The Element Song Empirical vs. Molecular Formula Molecular Formula C6H6 Empirical Formula CH CO2 CO2 C6H12O6 CH2O C2H4 CH2 C6H12O11 C6H12O11 Empirical Formula Empirical Formula - • Q. How do we get the Empirical Formula from the Molecular Formula??? ** Fill in the Empirical Formula for each of the following: Molecular Formula C2H2 C4H10 C5H10 C5H9 C3H9O3 Empirical Formula Converting Empirical Formula Molecular Formula: Steps: 1. Identify the mass of the molecular formula (given) 2. Calculate the gfm of Empirical formula. 3. Divide molecular mass (step 1) by empirical mass (step 2) and record answer. molecular _ mass x = empirical _ mass 4. Multiply subscripts of Empirical formula by the answer in step 3 to get the Molecular formula. Eg.1: The molecular mass of a substance is 48 a.m.u. and its empirical formula is CH4. What is the molecular formula of this substance? Eg.2: What is the molecular formula of a substance with a molecular mass of 30g and an empirical formula of CH3? Eg.3: A substance has an empirical formula of CH2O and a molecular mass of 180g. What is the molecular formula of this substance? Eg.4: A substance has an empirical formula of CO2 and a molecular mass of 44g. What is the molecular formula of this substance? Stoichiometry and Balancing Equations **Chemical Equations – used to represent chemical reactions. • In all chemical rxns., 3 types of Conservation take place: 1.) Mass 2.) Energy (Kinetics) 3.) Charge (#e- lost = #e- gained (Redox.)) **Important . . . Symbol , , , and = Meaning “yield”; separates reactants from products Stoichiometry ** Stoichiometry – branch of chemistry that deals with the amounts of substances that enters (reactants) and leaves (products) a chemical reaction. ** Stoichiometry • Coefficients = # moles of a compound – Eg. 5 _BaCl2 = 5 moles of BaCl2 • Subscripts = # moles of atoms (inside of a compound) – Eg. 3 _Al2S3 = ____ moles of the compound Al2S3, _____ moles of Aluminum atoms and ____ moles of Sulfur atoms. Stoichiometry 1.) __ Na + __ O2 __ Na2O SOC = 2.) __ Al + __ O2 __ Al2O3 SOC = Stoichiometry 3.) carbon + oxygen carbon dioxide SOC = **Remember “BrINClHOF”!!!** 4.) hydrogen + oxygen water SOC = Stoichiometry ___ AlCl3 + ____AgNO3 ____AgCl + ____Al(NO3)3 Link – Balancing Equations (timed) Link 2 – Balancing Equations Handout Stoichiometry Rule: 1.) If you change any coefficient in a balanced equation, you MUST change them all. 2.) To change coefficients, you must either multiply or divide by a number. Stoichiometry Eg.1: ___KClO3 ____KCl + ____O2 How many moles of Oxygen gas will be produced if you decompose 4 moles of KClO3? Stoichiometry Eg.2: ___Zn + ___CuCl ___ZnCl2 + ___Cu How many moles of CuCl were used if 10 moles of copper metal were produced? Stoichiometry Eg.3: ___ AlCl3 + ____AgNO3 ____AgCl + ____Al(NO3)3 How many moles of aluminum chloride must you use in the above reaction to produce 1.5 moles of silver chloride?