CHEMISTRY Matter and Change CHAPTER 10 Table Of Contents Section 10.1 Measuring Matter Section 10.2 Mass and the Mole Section 10.3 Moles of Compounds Chapter 10: The Mole Section 10.4 Empirical and Molecular Formulas Section 10.5 Formulas of Hydrates Click a hyperlink to view the corresponding slides. SECTION 10.1 Measuring Matter • 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. molecule: two or more atoms that covalently bond together to form a unit SECTION Measuring Matter 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. mole Avogadro’s number Chemists use the mole to count atoms, molecules, ions, and formula units. 10.1 SECTION 10.1 Exit Measuring Matter • 1 mole is the amount of atoms in 12 g of pure carbon12, or 6.02 1023 representative particles, which is any kind of particle – an atom, a molecule, a formula unit, an electron, an ion, etc. • The number is called Avogadro’s number. SECTION 10.1 Measuring Matter Converting Between Moles and Particles Converting Between Moles and Particles • Conversion factors must be used. (cont.) • Moles to particles • Particles to moles • Use the inverse of Avogadro’s number as the conversion factor. Number of molecules in 3.50 mol of sucrose 1 SECTION Mass and the Mole 10.2 • Relate the mass of an atom conversion factor: a to the mass of a mole of ratio of equivalent atoms. values used to express the same quantity in • Convert between number different units of moles and the mass of an element. • Convert between number of moles and number of atoms of an element. molar mass SECTION 10.2 Mass and the Mole The Mass of a Mole • 1 mol of copper (6.02 x 1023 atoms of copper) and 1 mol of carbon (6.02 x 1023 atoms of carbon) have different masses. • One copper atom has a different mass than 1 carbon atom. A mole always contains the same number of particles; however, moles of different substances have different masses. SECTION 10.2 Mass and the Mole SECTION 10.2 Mass and the Mole The Mass of a Mole (cont.) Using Molar Mass • Molar mass is the mass in grams of one mole of any pure substance. • Moles to mass • The molar mass of any element is numerically equivalent to its atomic mass and has the units g/mol. 3.00 moles of copper has a mass of 191 g. SECTION 10.2 Mass and the Mole SECTION 10.2 Mass and the Mole Using Molar Mass (cont.) Using Molar Mass (cont.) • Convert mass to moles with the inverse molar mass conversion factor. • This figure shows the steps to complete conversions between mass and atoms. • Convert moles to atoms with Avogadro’s number as the conversion factor. 2 SECTION 10.3 Moles of Compounds SECTION 10.3 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. • Recognize the mole relationships shown by a chemical formula. • Calculate the molar mass of a compound. • Convert between the number of moles and mass of a compound. • Apply conversion factors to determine the number of atoms or ions in a known mass of a compound. representative particle: an atom, molecule, formula unit, or ion SECTION 10.3 Moles of Compounds SECTION 10.3 Moles of Compounds Chemical Formulas and the Mole The Molar Mass of Compounds • Chemical formulas indicate the numbers and types of atoms contained in one unit of the compound. • 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. • One mole of CCl2F2 contains one mole of C atoms, two moles of Cl atoms, and two moles of F atoms. SECTION 10.3 Moles of Compounds Converting Moles of a Compound to Mass • For elements, the conversion factor is the molar mass of the compound. • The procedure is the same for compounds, except that you must first calculate the molar mass of the compound. • The molar mass of a compound demonstrates the law of conservation of mass. SECTION 10.3 Moles of Compounds Converting the Mass of a Compound to Moles • The conversion factor is the inverse of the molar mass of the compound. 3 SECTION 10.3 Moles of Compounds SECTION 10.3 Moles of Compounds Converting the Mass of a Compound to Number of Particles Converting the Mass of a Compound to Number of Particles (cont.) • Convert mass to moles of compound with the inverse of molar mass. • This figure summarizes the conversions between mass, moles, and particles. • Convert moles to particles with Avogadro’s number. SECTION 10.4 Empirical and Molecular Formulas • Explain what is meant by the percent composition of a compound. • Determine the empirical and molecular formulas for a compound from mass percent and actual mass data. percent by mass: the ratio of the mass of each element to the total mass of the compound expressed as a percent SECTION 10.4 Empirical and Molecular Formulas 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. percent composition empirical formula molecular formula A molecular formula of a compound is a whole-number multiple of its empirical formula. SECTION 10.4 Empirical and Molecular Formulas SECTION 10.4 Empirical and Molecular Formulas Percent Composition (cont.) Empirical Formula • The percent by mass of each element in a compound is the percent composition of a compound. • 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. • Percent composition of a compound can also be determined from its chemical formula. • 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 4 SECTION 10.4 Empirical and Molecular Formulas SECTION 10.5 Formulas of Hydrates Molecular Formula • The molecular formula specifies the actual number of atoms of each element in one molecule or formula unit of the substance. • Explain what a hydrate is and relate the name of the hydrate to its composition. • Molecular formula is always a whole-number multiple of the empirical formula. • Determine the formula of a hydrate from laboratory data. crystal lattice: a threedimensional geometric arrangement of particles hydrate Hydrates are solid ionic compounds in which water molecules are trapped. SECTION 10.5 Formulas of Hydrates SECTION 10.5 Formulas of Hydrates Naming Hydrates Analyzing a Hydrate • A hydrate is a compound that has a specific number of water molecules bound to its atoms. • When heated, water molecules are released from a hydrate leaving an anhydrous compound. • The number of water molecules associated with each formula unit of the compound is written following a dot. • To determine the formula of a hydrate, find the number of moles of water associated with 1 mole of hydrate. • Sodium carbonate decahydrate = Na2CO3 • 10H2O SECTION 10.5 Formulas of Hydrates SECTION 10.5 Formulas of Hydrates Analyzing a Hydrate (cont.) Use of Hydrates • Weigh hydrate. • Anhydrous forms of hydrates are often used to absorb water, particularly during shipment of electronic and optical equipment. • 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. • In chemistry labs, anhydrous forms of hydrates are used to remove moisture from the air and keep other substances dry. 5