TRO3_Lecture_06_CPS_Mod

# Since atoms are small the large number of atoms makes

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Since atoms are small, the large number of atoms makes sense. 1 mol = 6.022 x 10 23 atoms 2.45 mol Cu atoms Cu Check: Solution: Solution Map: Relationships: Given: Find: mol Cu atoms Cu mol 1 atoms 10 022 . 6 23 Cu atoms 10 1.48 mol 1 atoms 10 022 . 6 Cu mol 45 . 2 24 23 Tro's "Introductory Chemistry", Chapter 6 19 Relationship Between Moles and Mass The mass of one mole of atoms is called the molar mass . The molar mass of an element, in grams, is numerically equal to the element’s atomic mass, in amu. The lighter the atom, the less a mole weighs. The lighter the atom, the more atoms there are in 1 g. Tro's "Introductory Chemistry", Chapter 6 20 Mole and Mass Relationships Substance Pieces in 1 mole Weight of 1 mole Hydrogen 6.022 x 10 23 atoms 1.008 g Carbon 6.022 x 10 23 atoms 12.01 g Oxygen 6.022 x 10 23 atoms 16.00 g Sulfur 6.022 x 10 23 atoms 32.06 g Calcium 6.022 x 10 23 atoms 40.08 g Chlorine 6.022 x 10 23 atoms 35.45 g Copper 6.022 x 10 23 atoms 63.55 g 1 mole carbon 12.01 g 1 mole sulfur 32.06 g

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1/8/2014 5 Tro's "Introductory Chemistry", Chapter 6 21 Example 6.2 Calculate the Moles of Sulfur in 57.8 G of Sulfur. Since the given amount is much less than 1 mol S, the number makes sense. 1 mol S = 32.07 g 57.8 g S mol S Check: Solution: Solution Map: Relationships: Given: Find: g S mol S g 32.07 S mol 1 S mol .80 1 g 32.07 mol 1 S g 7.8 5 Tro's "Introductory Chemistry", Chapter 6 22 Example 6.2: Calculate the number of moles of sulfur in 57.8 g of sulfur. Tro's "Introductory Chemistry", Chapter 6 23 Example: Calculate the number of moles of sulfur in 57.8 g of sulfur. Write down the given quantity and its units. Given: 57.8 g S
1/8/2014 6 Tro's "Introductory Chemistry", Chapter 6 24 Write down the quantity to find and/or its units. Find: ? moles S Information: Given: 57.8 g S Example: Calculate the number of moles of sulfur in 57.8 g of sulfur. Tro's "Introductory Chemistry", Chapter 6 25 Collect needed conversion factors: 1 mole S atoms = 32.07 g Information: Given: 57.8 g S Find: ? moles S Example: Calculate the number of moles of sulfur in 57.8 g of sulfur. Tro's "Introductory Chemistry", Chapter 6 26 Write a solution map for converting the units: Information: Given: 57.8 g S Find: ? moles S Conversion Factor: 1 mole S = 32.07 g g S moles S S g 2.07 3 S mole 1 Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

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1/8/2014 7 Tro's "Introductory Chemistry", Chapter 6 27 Apply the solution map: S moles S g 2.07 3 S mole 1 S g 57.8 = 1.802307 moles S = 1.80 moles S Significant figures and round: Information: Given: 57.8 g S Find: ? moles S Conversion Factor: 1 mole S = 32.07 g Solution Map: g moles Example: Calculate the number of moles of sulfur in 57.8 g of sulfur. Tro's "Introductory Chemistry", Chapter 6 28 Check the solution: 57.8 g sulfur = 1.80 moles sulfur The units of the answer, moles, are correct. The magnitude of the answer makes sense since 57.8 g is more than 1 mole.

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