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Understanding the Mole in Chemistry

Learn how chemists use the mole to count particles of matter, convert between moles and particles, and determine the mass of a substance. Explore the relationships between moles, particles, and compounds in this comprehensive guide.

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Understanding the Mole in Chemistry

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  1. CHEMISTRY Matter and Change Chapter 10: The Mole

  2. Table Of Contents CHAPTER10 Section 10.1 Measuring Matter Section 10.2 Mass and the Mole Section 10.3 Moles of Compounds Section 10.4 Empirical and Molecular Formulas Section 10.5 Formulas of Hydrates Click a hyperlink to view the corresponding slides. Exit

  3. Measuring Matter SECTION10.1 Explain how a mole is used to indirectly count the number of particles of matter. molecule: two or more atoms that covalently bond together to form a unit Relate the mole to a common everyday counting unit. Convert between moles and number of representative particles. mole Avogadro’s number Chemists use the mole to count atoms, molecules, ions, and formula units.

  4. Measuring Matter SECTION10.1 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 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.

  5. Measuring Matter SECTION10.1 Converting Between Moles and Particles Conversion factors must be used. Moles to particles Number of molecules in 3.50 mol of sucrose

  6. Measuring Matter SECTION10.1 Converting Between Moles and Particles(cont.) Particles to moles Use the inverse of Avogadro’s number as the conversion factor.

  7. Section Check SECTION10.1 What does the mole measure? A.mass of a substance B.amount of a substance C.volume of a gas D.density of a gas

  8. Section Check A. B. SECTION10.1 What is the conversion factor for determining the number of moles of a substance from a known number of particles? C.1 particle  6.02  1023 D.1 mol  6.02  1023particles

  9. Mass and the Mole SECTION10.2 Relate the mass of an atom to the mass of a mole of atoms. conversion factor: a ratio of equivalent values used to express the same quantity in different units Convert between number of moles and the mass of an element. Convert between number of moles and number of atoms of an element. molar mass A mole always contains the same number of particles; however, moles of different substances have different masses.

  10. Mass and the Mole SECTION10.2 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.

  11. Mass and the Mole SECTION10.2 The Mass of a Mole(cont.) 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.

  12. Mass and the Mole SECTION10.2 Using Molar Mass Moles to mass 3.00 moles of copper has a mass of 191 g.

  13. Mass and the Mole SECTION10.2 Using Molar Mass(cont.) Convert mass to moles with the inverse molar mass conversion factor. Convert moles to atoms with Avogadro’s number as the conversion factor.

  14. Mass and the Mole SECTION10.2 Using Molar Mass(cont.) This figure shows the steps to complete conversions between mass and atoms.

  15. Section Check SECTION10.2 The mass in grams of 1 mol of any pure substance is: A.molar mass B.Avogadro’s number C.atomic mass D.1 g/mol

  16. Section Check SECTION10.2 Molar mass, in its un-inverted form, is used to convert what? A.mass to moles B.moles to mass C.atomic weight D.particles

  17. Moles of Compounds SECTION10.3 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

  18. Moles of Compounds SECTION10.3 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.

  19. Moles of Compounds SECTION10.3 Chemical Formulas and the Mole 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.

  20. Moles of Compounds SECTION10.3 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.

  21. Moles of Compounds SECTION10.3 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.

  22. Moles of Compounds SECTION10.3 Converting the Mass of a Compound to Moles The conversion factor is the inverse of the molar mass of the compound.

  23. Moles of Compounds SECTION10.3 Converting the Mass of a Compound to Number of Particles Convert mass to moles of compound with the inverse of molar mass. Convert moles to particles with Avogadro’s number.

  24. Moles of Compounds SECTION10.3 Converting the Mass of a Compound to Number of Particles (cont.) This figure summarizes the conversions between mass, moles, and particles.

  25. Section Check SECTION10.3 How many moles of OH— ions are in 2.50 moles of Ca(OH)2? A.2.00 B.2.50 C.4.00 D.5.00

  26. Section Check SECTION10.3 How many particles of Mg are in 10 moles of MgBr2? A.6.02  1023 B.6.02  1024 C.1.20  1024 D.1.20  1025

  27. Empirical and Molecular Formulas SECTION10.4 Explain what is meant by the percent composition of a compound. percent by mass: the ratio of the mass of each element to the total mass of the compound expressed as a percent Determine the empirical and molecular formulas for a compound from mass percent and actual mass data. percent composition empirical formula molecular formula A molecular formula of a compound is a whole-number multiple of its empirical formula.

  28. Empirical and Molecular Formulas SECTION10.4 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.

  29. Empirical and Molecular Formulas SECTION10.4 Percent Composition(cont.) The percent by mass of each element in a compound is the percent composition of a compound. Percent composition of a compound can also be determined from its chemical formula.

  30. Empirical and Molecular Formulas SECTION10.4 Empirical Formula The empirical formulafor 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

  31. Empirical and Molecular Formulas SECTION10.4 Molecular Formula The molecular formula specifies the actual number of atoms of each element in one molecule or formula unit of the substance. Molecular formula is always a whole-number multiple of the empirical formula.

  32. Empirical and Molecular Formulas SECTION10.4 Molecular Formula(cont.)

  33. Section Check SECTION10.4 What is the empirical formula for the compound C6H12O6? A.CHO B.C2H3O2 C.CH2O D.CH3O

  34. Section Check SECTION10.4 Which is the empirical formula for hydrogen peroxide? A.H2O2 B.H2O C.HO D.none of the above

  35. Formulas of Hydrates SECTION10.5 Explain what a hydrate is and relate the name of the hydrate to its composition. crystal lattice:a three-dimensional geometric arrangement of particles Determine the formula of a hydrate from laboratory data. hydrate Hydrates are solid ionic compounds in which water molecules are trapped.

  36. Formulas of Hydrates SECTION10.5 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

  37. Formulas of Hydrates SECTION10.5 Naming Hydrates(cont.)

  38. Formulas of Hydrates SECTION10.5 Analyzing a Hydrate 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.

  39. Formulas of Hydrates SECTION10.5 Analyzing a Hydrate(cont.) 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.

  40. Formulas of Hydrates SECTION10.5 Use of Hydrates Anhydrous forms of hydrates are often used to absorb water, particularly during shipment of electronic and optical equipment. In chemistry labs, anhydrous forms of hydrates are used to remove moisture from the air and keep other substances dry.

  41. Section Check SECTION10.5 Heating a hydrate causes what to happen? A.Water is driven from the hydrate. B.The hydrate melts. C.The hydrate conducts electricity. D.There is no change in the hydrate.

  42. Section Check SECTION10.5 A hydrate that has been heated and the water driven off is called: A.dehydrated compound B.antihydrated compound C.anhydrous compound D.hydrous compound

  43. The Mole CHAPTER10 Study Guide Chemistry Online Study Guide Chapter Assessment Standardized Test Practice

  44. Measuring Matter SECTION10.1 Study Guide Key Concepts The mole is a unit used to count particles of matter indirectly. One mole of a pure substance contains Avogadro’s number of particles. Representative particles include atoms, ions, molecules, formula units, electrons, and other similar particles. One mole of carbon-12 atoms has a mass of exactly 12 g. Conversion factors written from Avogadro’s relationship can be used to convert between moles and number of representative particles.

  45. Mass and the Mole SECTION10.2 Study Guide Key Concepts The mass in grams of 1 mol of any pure substance is called its molar mass. The molar mass of an element is numerically equal to its atomic mass. The molar mass of any substance is the mass in grams of Avogadro’s number of representative particles of the substance. Molar mass is used to convert from moles to mass. The inverse of molar mass is used to convert from mass to moles.

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