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Quantities in Chemistry The Relationship Between Mole and Molar Mass

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Mole Review A Mole is a unit of measurement in chemistry. It represents 6.02 x 10 23 of an entity. One mole of sodium is 6.02 x 10 23 atoms of sodium. The symbol for mole is “n”. The unit for mole is “mol” 6.02 x 10 23 is also known as Avogadro’s number.

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How do we measure out 1 mol? Do you count out 6.02 x 10 23 atoms in the lab? Do you use special equipment? Can you measure it as a volume? Can you measure it as a mass?

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Amazing! 1 mole = amu of the element in grams For Example: 1 mol of H atoms = 1 mol of O atoms = 1 mol of C atoms = 1 mol of Na atoms = 1 mol of Au atoms = 1.01g 16.0g 12.01g 22.99g 197.0g

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Molar Mass Molar Mass (MM) is the mass (in grams) of one mole of a substance. The formula for molar mass is For example, Hydrogen’s molar mass = 1.01 g/mol

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Molar Mass of Compounds The molar mass of a compound is equal to the sum of the molar masses of the atoms in the molecules or ions in the compound. For example, the molar mass of water is: M H 2 O = 2(M H ) + (M O ) = 2(1.01g/mol) + 1(16.0g/mol) =18.02 g/mol

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Example: Find the molar mass of H 2 CO 2 M H 2 CO 2 = 2(M H ) + (M C ) +2(M O ) = 2(1.01g/mol) + (12.00g/mol) + 2(16.0g/mol) =46.02 g/mol

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Atoms, Moles, Mass & Molar Mass Calculations Example 1: Calculate the molar mass of magnesium if 0.330 mol has a mass of 8.02 g M=m/n = 8.02g/0.330mol = 24.3g/mol

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Atoms, Moles, Mass & Molar Mass Calculations Example 2: Calculate the mass, in grams, of 2.00 mol of calcium atoms. M=m/n m = M x n = 40.08g/mol x 2.0 mol = 80.2g

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Atoms, Moles, Mass & Molar Mass Calculations Example 3: How many moles of gold are in 275.8g of pure gold? M=m/n n = m/M = 275.8g / 197.0 g/mol = 1.400 mol

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Calculating Number of Atoms If you have a mass of the number of moles of an item, you can determine the number of molecules in an amount of an element using Avogadro’s number. Avogadro’s number = 6.02 x 10 23 particles/mol

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Atom Calculations Example 4: How many atoms of gold are in a 232.8g of pure gold? Step 1: Determine the number of moles n = m/M = 232.8g / 197.0g/mol = 1.182 mol Step 2: Using Avogadro’s number and the number of moles, determine the number of particles. N= n x NA = 1.182 mol x 6.02 x 10 23 particles/mol = 7.12 x 10 23 particles Step 3: Determine the number of atoms per particle, and multiply Atoms = (1atom/particle)(7.10 x10 23 particles) = 7.10 x10 23 atoms

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Atom Calculations Example 5: How many atoms of oxygen are in a 230.0g of oxygen gas? Step 1: Determine the number of moles n = m/M = 230.0g / 32.0g/mol = 7.188 mol Step 2: Using Avogadro’s number and the number of moles, determine the number of atoms. N= n x NA = 7.188mol x 6.02 x 10 23 atoms/mol = 4.327 x 10 24 atoms Step 3: Determine the number of atoms per particle, and multiply Atoms = (2 oxygens)(4.327x10 24 atoms) = 8.654 x10 24 atoms of oxygen

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