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Chapter 6 Chemical Calculations: Formula Masses, Moles, & Chemical Equations Atomic Mass = the weighted average of masses of all naturally-occurring isotopes of an element Formula Mass = the sum of the atomic masses of all the atoms represented in the chemical formula Calculate the Formula Mass: SnF2 Al(OH)3 The Mole A chemistry counting unit! 1 Mole of an element = the atomic mass in grams How much is a mole? 1 mole of Al 1 mole of H2O 1 mole of NaCl #/type of particles molar mass 1 Mole of any element contains the same number of atoms as 1 mole of any other element 1 Mole of a molecular compound contains the same number of molecules as 1 mole of any other molecular compound 1 Mole of an ionic compound contains the same number of formula units as 1 mole of any other ionic compound Particles Moles Grams The Mole = a Chemistry Counting Unit 1. Find the number of atoms in 3.00 moles of copper: 3.00 mole Cu x 6.02 x 1023 atoms = mole Cu 2. Find the number of molecules in 0.485 mole of CO2. 3. How many moles of water contain 7.50 x 1025 molecules? 4. How many moles of silicon are represented by 1.55 x 1020 atoms of silicon? What does a mole look like? Copper Cu Carbon C Water H2O Sugar C6H12O6 Salt NaCl Calculating Molar Mass of a Compound H2O C2H6O (NH4)2Cl Converting Mass to Moles (element) mass (g) x 1 mole = moles molar mass (g) Example: How many moles of copper are in 5.00 grams of copper? Converting Moles to Mass moles x molar mass (g) = mass (g) 1 mole Example: How many grams of copper are equal to 6.25 mole of copper? Converting Mass to Moles (compound) mass (g) x 1 mole = moles molar mass (g) Example: A box of salt contains 737 grams of NaCl. How many moles of NaCl are present? Converting Moles to Mass moles x molar mass (g) = mass (g) 1 mole Example: How many grams of ethanol (C2H6O) are equivalent to 2.6 x 103 moles of ethanol? Converting Mass to Atoms mass (g) x 1 mole x molar mass (g) 6.02 x 1023 atoms = # of atoms 1 mole Example: How many atoms of copper are in 25.0 grams of copper? Example: Find the number of gold atoms in a ring that contains 12.8 grams of gold. Moles of Elements in a Formula Subscripts in a chemical formula indicate the number of atoms of each type of element in a molecule: Writing and Balancing Chemical Equations 1. Write an equation using the correct formulas of reactants & products. CH4(g) + O2(g) CO2(g) + H2O(l) 2. The State may be specified solid (s) liquid (l) gas (g) aqueous (aq) 3. Conditions may be written above or below the arrow heat catalyst Pt Writing and Balancing Chemical Equations 1. Use Coefficients (in front of formula) to balance 2. Hints: 3. start with the element that has the largest number of atoms do H & O next save free elements for last treat polyatomic ions as single entities (if they do not change) Don’t change any subscripts! CH4(g) + O2(g) Count atoms of each element: C H O Use coefficients to balance each element: CO2(g) + H2O(l) Writing and Balancing Chemical Equations Al(s) + Cl2(g) AlCl3(s) C3H8(g) + O2(g) CO2(g) + H2O(l) Writing and Balancing Chemical Equations Mg(s) + HCl(aq) MgCl2(aq) + H2(g) Fe(s) + O2(g) Fe2O3(s) Balancing Equations with Polyatomic Ions: Na2SO4(aq) + BaCl2(aq) Count ions on each side: NaCl(aq) + BaSO4(s) Balancing Equations with Polyatomic Ions: Na3PO4(aq) + MgCl2(aq) NaCl(aq) + Mg3(PO4)2(s) NaOH(aq) + H2SO4(aq) Na2SO4(aq) + H2O(l) Recognizing Reactions by Pattern (Chapter 9.1): Combination Reactions Decomposition Reactions Single Replacement Reactions (Displacement) Double Replacement Reactions (Exchange) Exchange of Cations & Anions (Double Replacement Rxn) 1. Formation of an insoluble product = precipitation AgNO3(aq) + NaCl(aq) 2. AgCl(s) + NaNO3(aq) Formation of a molecular liquid (like water) = neutralization HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) 3. Evolution of a gas HCl(aq) + NaHCO3(aq) NaCl(aq) + H2CO3(aq) H2O(l) + CO2(g) Classify as Decomposition, Combination, Single Replacement or Double Replacement; Name all compounds/elements: 1. Na2S + CuCl2 2 NaCl + CuS 2. Ca + Cl2 CaCl2 3. CaCO3 CaO + CO2 4. Zn + CuCl2 ZnCl2 + Cu Balance & Classify as Decomposition, Combination, Single Replacement or Double Replacement 1. Ca + O2 CaO 2. KClO3 KCl + O2 3. ZnCl2 + AgNO3 Zn(NO3)2 + AgCl 4. Zn + HCl ZnCl2 + H2 5. Fe + O2 Fe2O3 6. BaCl2 + K2SO4 BaSO4 + KCl Balance & Classify as Decomposition, Combination, Single Replacement or Double Replacement 1. CaCl2 + Na2CO3 2. Fe2S3 3. Ca + Cl2 CaCO3 + NaCl Fe + S CaCl2 4. Cu + AgNO3 Cu(NO3)2 + Ag 5. PbO + HNO3 Pb(NO3)2 + H2O We can also classify chemical reactions by Reaction Type Combustion Reactions – give off heat & light CH4(g) + 2 O2 (g) CO2(g) + 2 H2O(g) Combustion Reactions Reaction of a carbon-containing compound with oxygen to generate heat and light Combustion of a hydrocarbon gives carbon dioxide & water: 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g) Combustion of a carbohydrate gives carbon dioxide & water: C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(g) Classification by Reaction Type Acid-Base Reactions (Neutralization) – give a salt & water H2SO4(aq) + KOH(aq) Precipitation Reactions – an insoluble compound is produced ZnCl2(aq) + AgNO3(aq) Oxidation-Reduction Reactions – involve an exchange of electrons Zn(s) + CuSO4(aq) Mole Relationships in Chemical Equations Conservation of Mass: in any chemical reaction, the total mass of the reactants is equal to the total mass of the products. 2Ag (s) + S(s) Atoms: Moles: Mass: Total mass: Ag2S(s) Chemical Calculations Using Chemical Equations 28.60 grams of copper reacts with 7.22 grams of sulfur in a combination reaction: Cu + S Mass: 28.60 Moles: Molar Ratio: What is the product? 7.22 ? 35.82 grams Empirical Formula of a Hydrate (lab) 5.00 g of CaCl2XH2O were heated. 3.78 g of the anhydrous salt remain. a) Write a chemical equation for the decomposition of the hydrate. CaCl2XH2O(s) a) Find the Formula of the hydrate.