The Mole Mr. Solsman Chapter 10 Goals • Explain how a mole is used to indirectly count the number of particles of matter. • Relate the mole to a common everyday counting unit. • Convert between moles and number of representative particles Counting Particles • Chemists need a convenient method for accurately counting the number of atoms, molecules, or formula units of a substance. • The mole is the SI base unit used to measure the amount of a substance. • 1 mole is the amount of atoms in 12 g of pure carbon-12, or 6.02 1023 atoms. • The number is called Avogadro’s number. Conversion factors must be used • Moles to particles Number of molecules in 3.50 mol of sucrose • Particles to moles • 1. How many zinc atoms are there in 2.50 mole of Zn? • 2. Calculate the number of molecules in 11.5 mol of water. • 3. How many formula units of silver nitrate are in 3.25 moles of silver nitrate? • 4. How many moles contain each of the following? • 5.75 x 1024 atoms of Al • 2.50 x 1020 atoms of Fe The Mass of a Mole • 1 mol of copper and 1 mol of carbon have different masses. • One copper atom has a different mass than 1 carbon atom. • Molar mass is the mass in grams of one mole of any pure substance. • The molar mass of any element is numerically equivalent to its atomic mass and has the units g/mol. Using Molar Mass 3.00 moles of copper has a mass of 191 g. • 1. Determine the mass of each of the following: • 3.57 mol Al • 42.6 mol Si • 2. Convert the moles given to mass in grams: • 3.45 x 102 mol Co • 2.45 x 10-2 mol Zn • 3. Convert each mass to moles: • 300.0 g S • 1.00 kg Cr • 0.120 kg Ti Moles of Compounds • The molar mass of a compound can be calculated from its chemical formula and can be used to convert from mass to moles of that compound. • Chemical formulas indicate the numbers and types of atoms contained in one unit of the compound. • One mole of CCl2F2 contains one mole of C atoms, two moles of Cl atoms, and two moles of F atoms. The Molar Mass of Compounds • The molar mass of a compound equals the molar mass of each element, multiplied by the moles of that element in the chemical formula, added together. • The molar mass of a compound demonstrates the law of conservation of mass. • 1. Find the molar mass of NaOH • 2. CaCl2 • 3. KC2H3O2 • 4. Sr(NO3)2 • 5. Determine the number of moles present: • 22.6 g AgNO3 • 6.50 g ZnSO4 • 35.0 g HCl • 25.4 mg PbCl4 • 6. Ethanol (C2H5 OH) is often blended with gasoline. A lab sample of ethanol has a mass of 45.6 grams. • A. How many moles of ethanol are present? • B. How many moles of carbon atoms are present? • C. How many carbon atoms are present? • Percent Composition • The percent by mass of any element in a compound can be found by dividing the mass of the element by the mass of the compound and multiplying by 100. • What is the percent by mass of oxygen in 36.0 grams of water if it contains 16 grams of oxygen? • The percent by mass of each element in a compound is the percent composition of a compound. • Sodium hydrogen carbonate (NaHCO3 ) also called baking soda is an active ingredient in antacids. Determine the percent composition of the compound. • Sucrose commonly called table sugar, has the formula C12 H22 O11. Find the percent composition. Empirical Formula • The empirical formula for a compound is the smallest whole-number mole ratio of the elements. You can calculate the empirical formula from percent by mass by assuming you have 100.00 g of the compound. Then, convert the mass of each element to moles. • The empirical formula may or may not be the same as the molecular formula. Molecular formula of hydrogen peroxide = H2O2 Empirical formula of hydrogen peroxide = HO The molecular formula specifies the actual number of atoms of each element in one molecule or formula unit of the substance. A molecular formula is always a whole-number multiple of the empirical formula. • Propane is a hydrocarbon composed of only carbon and hydrogen. If a sample is 81.82% carbon and 18.18% hydrogen, what is its empirical formula? • Methyl acetate is a solvent used in paints, etc. Determine the empirical formula for a sample that has the following analysis: • 48.64% carbon, 8.16% hydrogen, and 43.20% oxygen. • Aspirin is the world’s most often used medication. The chemical analysis of aspirin indicates that the molecule is 60.00% carbon, 4.44% hydrogen, and 35.56% oxygen. What is its empirical formula? • A sample of the mineral ilmenite contains 5.41 g of iron, 4.64 g Titanium, and 4.65 g oxygen. Determine its empirical fomula. • A compound was found to contain 49.98 g of carbon and 10.47 g of hydrogen. The molar mass of the compound is 58.12 g/mol. Find the molecular formula. • A chemical analysis of Vitamin D yielded data that gave 84.31% carbon, 11.53% hydrogen, and 4.16% oxygen. The molar mass was found to be 384 g/mol. What is its empirical and molecular and empirical formulas? Naming Hydrates • A hydrate is a compound that has a specific number of water molecules bound to its atoms. • The number of water molecules associated with each formula unit of the compound is written following a dot. • Sodium carbonate decahydrate = Na2CO3 • 10H2O • When heated, water molecules are released from a hydrate leaving an anhydrous compound. • To determine the formula of a hydrate, find the number of moles of water associated with 1 mole of hydrate. • • • • • Weigh hydrate. Heat to drive off the water. Weigh the anhydrous compound. Subtract and convert the difference to moles. The ratio of moles of water to moles of anhydrous compound is the coefficient for water in the hydrate. • An 11.75 gram sample of a common hydrate of cobalt(II) chloride is heated. After heating, 0.0712 mol of anhydrous cobalt chloride remains. What is the formula and name of the hydrate?