Ch. 11 The Mole The Mol House The Mol House Atoms in a molecule molecules molgrams Molar Mass Avogadro’s number Chemical formula.

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Presentation transcript:

Ch. 11 The Mole The Mol House The Mol House Atoms in a molecule molecules molgrams Molar Mass Avogadro’s number Chemical formula

Examples How many grams are in 4.14x10 23 molecules of calcium hydroxide? How many grams are in 4.14x10 23 molecules of calcium hydroxide? How many atoms of hydrogen are in 2.56mol of C 3 H 8 ? How many atoms of hydrogen are in 2.56mol of C 3 H 8 ?

Empirical Formula 1. Convert to mol using periodic table to find the molar masses 1. Convert to mol using periodic table to find the molar masses If you are given percents, assume you have 100.0g of a sample so your percents become your grams If you are given percents, assume you have 100.0g of a sample so your percents become your grams 2. Divide by the smallest mol 2. Divide by the smallest mol Your answer should be either a whole number or a recognizable fraction (.25,.33,.5,.67,.75) Your answer should be either a whole number or a recognizable fraction (.25,.33,.5,.67,.75) 3. Use the ratio from dividing to create your formula. 3. Use the ratio from dividing to create your formula.

EF example A compound is known to contain 5.88% hydrogen and 94.12% oxygen. What is the empirical formula? A compound is known to contain 5.88% hydrogen and 94.12% oxygen. What is the empirical formula?

Molecular Formula 1. Find the Empirical Formula 1. Find the Empirical Formula 2. Divide the molecular mass (GIVEN) by the molar mass of your empirical formula. 2. Divide the molecular mass (GIVEN) by the molar mass of your empirical formula. Your answer should be exactly a whole number. If not, you did something wrong. Your answer should be exactly a whole number. If not, you did something wrong. 3. Multiply your EF by the number you get from step 2. This is your Molecular Formula. 3. Multiply your EF by the number you get from step 2. This is your Molecular Formula.

Molec. Formula, cont’d The molecular mass of the chemical from the previous problem is 34.0g/mol. Find the molecular formula. The molecular mass of the chemical from the previous problem is 34.0g/mol. Find the molecular formula.