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Bell Ringer

Bell Ringer. What is a Mole? What is the mass of a NaCl molecule?. Chapter 7.1b. Molar Mass. Common counting units: shoes by the pair (pair = 2) eggs by the dozen (dozen = 12) paper by the ream (ream = 500 sheets). Counting With Moles.

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Bell Ringer

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  1. Bell Ringer • What is a Mole? • What is the mass of a NaCl molecule?

  2. Chapter 7.1b Molar Mass

  3. Common counting units: • shoes by the pair (pair = 2) • eggs by the dozen (dozen = 12) • paper by the ream (ream = 500 sheets).

  4. Counting With Moles • Chemical reactions usually involve very large numbers of tiny particles • We use a counting unit called the mole to measure amounts of a substance. • Mole (mol) = amount of any substance that contains approximately 6.02 × 1023particles. • This amount is known as Avogadro’s number. • Ex: 1 mole of iron = 6.02 × 1023 atoms of iron.

  5. Molar Mass: • mass of one mole of a substance • same as atomic mass, in grams. Examples: • Carbon: • Atomic mass = 12.0 amu • Molar mass = 12.0 grams. • Sulfur: • Atomic mass = 32.1 amu • Molar mass = 32.1 grams.

  6. Counting With Moles • Molar Mass of a compound = • sumof atomic masses of all its atoms, expressed in grams. • Tells us the total grams in one mole of the compound Example: Carbon dioxide (CO2) • 1 carbon atom = 12.0 amu • 2 oxygen atoms = (2 ×16.0 amu) =32.0 amu • CO2atomic mass = (12.0 + 32.0) = 44.0 amu • CO2molar mass = 44.0 grams • 44.0g CO2 in 1 mol CO2

  7. Mole-Mass Conversions • Knowing the molar mass of a substance lets you easily convert between moles and mass • “converting” means you can calculate one from the other Example: • Molar mass of CO2 is 44.0 grams 1.0 mole of CO2 = 44.0 grams • Conversion factors  OR

  8. Converting Example: Chocolate Cake Recipe Recipe calls for 4 eggs per cake and you plan to make 3 cakes. Eggs can only be bought by the dozen (i.e. groups of 12). How may dozen eggs do you need to buy? Conversion factors: 4 eggs1 cake 1 cake 4 eggs 12 eggs1 doz. eggs 1 doz. eggs 12 eggs Calc: 3 cakes x 4 eggs x 1 doz eggs = 1 doz eggs 1 cake 12 eggs

  9. Counting With Moles • You have 55.0 grams of CO2. How many moles? • To calculate how many moles of CO2 you have, multiply the mass by a conversion factor. • You can check your answer.

  10. Chemical Calculations • In chemical reactions, the mass of a reactantor productcan be calculated. • Use a balanced chemical equation and the molar masses of the reactants and products.

  11. Chemical Calculations • In a balanced chemical equation, the number of atoms of each element on the left equals the number of atoms of each element on the right.

  12. Chemical Calculations • The Coefficienttells us the # of moles of each reactant and product involved the reaction

  13. Chemical Calculations • Molar Mass = the # of grams per mole of each reactant and product

  14. Chemical Calculations • Mass (of a reactant or product) = • the # of moles in the balanced equation (Coefficient) x the molar mass.

  15. Chemical Calculations - Stoichiometry Converting Mass to Moles To calculate how much oxygen is required to make 144 grams of water, begin with a balanced chemical equation for the reaction. 2H2 +O22H2O • Determine how many moles of water you are trying to make. • Convert the given mass (144g) of water into moles.

  16. Chemical Calculations Using Mole Ratios • Write the conversion factors, or mole ratios. • 2H2 +O22H2O • Calculate how many moles of oxygen are required to produce eight moles of water.

  17. Chemical Calculations Converting Moles to Mass • Convert moles of O2 to grams of O2 by using the molar mass of O2 as a conversion factor. • To produce 144 grams of H2O, you must supply 128 grams of O2.

  18. Assessment Questions • Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? • Al + NH4ClO4 —› Al2O3 + NH4Cl • 4Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl • 8Al + NH4ClO4 —› 4Al2O3 + NH4Cl • 8Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl

  19. Assessment Questions • Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? • Al + NH4ClO4 —› Al2O3 + NH4Cl • 4Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl • 8Al + NH4ClO4 —› 4Al2O3 + NH4Cl • 8Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl ANS: D

  20. Assessment Questions • How many moles of NaCl (molar mass = 58.5) are there in a 5.85-gram sample? • 58.5 mol • 5.85 mol • 0.10 mol • 0.28 mol

  21. Assessment Questions • How many moles of NaCl (molar mass = 58.5) are there in a 5.85-gram sample? • 58.5 mol • 5.85 mol • 0.10 mol • 0.28 mol ANS: C

  22. Assessment Questions • In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?2K + 2H2O —› 2KOH + H2 • 2.5 g • 5 g • 10 g • 20 g

  23. Assessment Questions • In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?2K + 2H2O —› 2KOH + H2 • 2.5 g • 5 g • 10 g • 20 g ANS: C

  24. Assessment Questions • In the chemical equation below, the reactants are carbon dioxide and water.CH4 + 2O2 —› CO2 +2H2OTrue <or> False? ANS: False, products

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