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Formula Mass vs. Gram Formula Mass AMUs vs Grams Aim: How can we find the formula mass and gram formula mass of a compound? Essential Questions: 1. How can we find the formula mass and gram formula mass of a compound? Key Words: mole, Atomic Mass Unit (AMU), formula mass, gram formula mass, empirical formula, molecular formula 2. What is the difference between empirical and molecular formulas. 2. What is the purpose of finding the gram formula mass of a compound? Explain. Smallest Unit of a Compound? If I have a beaker of water, what is the smallest unit of that substance? H2O The formula of water is the smallest unit of water. Formula Mass If the formula is the smallest unit of a substance, how do we calculate the formula mass of a substance? We take the sum of the atomic masses of that substance. Let’s find the formula mass for: Al: _____ O2: _____ Sodium Sulfate: _____ How do we find the atomic mass of Sodium Sulfate? Step 1 : Write the correct formula! Na2SO4 Element Atomic Mass # of Atoms (Subscript) Total x = x = x = Formula Mass: Always Expressed in AMU! Picture This! You are a chemical technician. A chemist asks you for 1 AMU of Na2SO4 How will you give it to him? What will you do? Convert to Grams Gram Formula Mass! Find the Gram Formula Mass for Glucose Element Atomic Mass # of Atoms (Subscript) Total x = x = x = Find the Gram Formula Mass of Zirconium Phosphate Element Atomic Mass # of Atoms (Subscript) Total x = x = x = HW Find the gram formula mass for the sheet from (1) KMuO4 to (11) H2CO3 (Notes) I. Formula Mass A. The Formula of a substance is the smallest unit of that substance. B. Calculating the Formula Mass of a substance 1. Step 1: Find the correct formula 2. Step 2: Find the gram atomic masses of each element (see periodic table and round off number to the nearest tenth). 3. Step 3: Multiply each atomic mass by the subscript in the formula. 4. Step 4: Find the sum of the masses. (Notes) A. Use the following chart to avoid errors B. The formula mass is always expressed in AMU’s (Notes) II. Gram Formula Mass A. Convert formula mass to grams and you will have the gram formula mass.