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Date:Tuesday, 15 June 2021 Unit 9: The Mole Outcomes: By the end of the lesson you should be able to do these things. What should I do if I cannot do one or more of these things? Keywords For every lesson there will be a list of key words here. • • • • • Topic 1: Measuring Matter Topic 2: Mass and the Mole Topic 3: Moles of compounds Topic 4: Empirical and molecular formulas Topic 5: Formulas of Hydrates Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Empirical and Molecular Formulas Starter: The molecular formula for succinic acid is C4H6O4. The empirical formula for succinic acid is C2H3O2. What do you think the difference is between molecular and empirical formula? Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass What is the difference between molecular formula and empirical formula? The molecular formula specifies the actual number of atoms of each element in one molecular formula unit of a substance. e.g. Ethane is C2H6 Ethane: C2H6 The empirical formula of a compound gives you the simplest whole number ratio of the elements in a compounds. e.g. ethane is CH3. Sometimes the empirical and the molecular formulae of a compound are the same, like for water, H2O. Water: H2O Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass TASK: Match the correct empirical formula Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Percent Composition from experimental data • The percent by mass of a compound shows us how much of each type of element are in a given sample of a substance. • It can be calculated by dividing the mass of the element by the mass of the compound and multiplying by a 100. • Percent by mass (element) = mass of element x 100 mass of compound Worked example: A 100 g sample of a compound contains 55g of Element X and 45g of Element Y. Calculate the percent composition of this sample. Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Percent Composition from chemical formula • Percent composition can also be determined from chemical formula. • To do this, assume that you have 1 mol of the compound – so we can use the molar mass of the compound. • Percent by mass = mass of element (in 1 mol of compound) x 100 molar mass of compound Worked example: Page 315, Example 10. Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Calculating percentage by mass – example 2 What percentage by mass of nitrogen is in ammonia (NH3)? (atomic mass: H = 1, N = 14) Step 1: Work out the molar mass of NH3. Molar mass of NH3 = 1 nitrogen atom + 3 hydrogen atoms = (1 x 14) + (3 x 1) = 17 Step 2: Work out the percentage by mass of nitrogen. Atomic mass x number of atoms % of nitrogen in NH3 = Molar mass of compound (14 x 1) = 17 = 82% x 100 x 100 Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Task: Calculate the percent by mass of… • Na in NaOH • S in CuSO4 • O in Ba(OH)2 • Cl in CaCl2 • Ca in CaCO3 • Al in Al2O3 • N in AgNO3 Lesson 2 ---Contd starter Empirical Formula – Rhyme to Remember “Percent to mass; Mass to mole; Divide by small; Multiply ‘til whole” Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Empirical Formula • Percent composition or masses of the elements in a given mass of compound can be used to determine the formula for the compound. • If percent composition is given, assume the total mass of the compound is 100g… • For example: The percent composition of a compound is 40.05% S and 59.95% O. • In 100g of this compound, we would have 40.05 g S and 59.95 g of O. • We then can convert these masses into moles… • This provides a mole ratio – divide by the smallest number if they are not whole numbers. • You now have the empirical formula. Date:Tuesday, 15 June 2021 Outcomes: 1. Calculate percent composition from experimental data and from the chemical formula. 2. Determine the empirical formula from percent composition and from mass data. 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass Task 1 ( 5 min) • What is the empirical formula of a compound that contains 60g of Carbon, 13g of hydrogen and 27g of oxygen? Solve this questions now ! Date:Tuesday, 15 June 2021 Outcomes: Molecular Formula 1. Calculate percent composition from experimental data and from the chemical formula. • To determine molecular formula, we must compare the molar mass of the compound (experimentally determined) with the mass of the empirical formula. 2. Determine the empirical formula from percent composition and from mass data. • Experimentally determined molar mass = n 3. Determine the molecular formula by comparing the molar mass. Keywords Empirical formula Molecular formula Molar mass Percent by mass mass of empirical formula • Molecular formula = n(empirical formula)

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