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Chapter 7 Chemical Quantities Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Atomic Mass Atomic mass is the Mass of a single atom in atomic mass units (amu) Mass of an atom compared to a 12 C atom Number below the symbol of an element

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Periodic Table and Atomic Mass Ag has atomic mass = 107.9 amu C has atomic mass = 12.01 amu S has atomic mass = 32.07 amu

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Atomic Mass Factors The atomic mass, Can be written as an equality Example: 1 P atom = 30.97 amu Can be written as two conversion factors Example: 1 P atom and 30.97 amu 30.97 amu 1 P atom

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Uses of Atomic Mass Factors The atomic mass is used to convert: A specific number of atoms to mass (amu) An amount in amu to number of atoms

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Learning Check What is the mass in amu of 75 silver atoms? 1) 107.9 amu 2) 8093 amu 3) 1.439 amu Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Learning Check How many gold atoms have a mass of 1.85 x 10 5 amu? 1) 939 Au atoms 2) 3.64 x 10 7 Au atoms 3) 106 Au atoms Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Formula Mass The formula mass is The mass in amu of a compound The sum of the atomic masses of the elements in a formula

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Calculating Formula Mass To calculate formula mass of Na 2 SO 4, Multiply the atomic mass of each element by its subscript Total the masses 2 Na x 22.99 amu = 45.98 amu Formula mass 1 Na 2 SO 4 1 S x 32.07 amu = 32.07 amu 142.05 amu 1 S 4 O x 16.00 amu = 64.00 amu 1 O

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Learning Check Using the periodic table, calculate the formula mass of aluminum sulfide Al 2 S 3.

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Collection Terms A collection term states a specific number of items. 1 dozen donuts = 12 donuts 1 ream of paper = 500 sheets 1 case = 24 cans Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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A mole (mol) is a collection that contains: The same number of particles as there are carbon atoms in 12.01 g of carbon 6.022 x 10 23 atoms of an element (Avogadro’s number). 1 Mol element Number of Atoms 1 mol C = 6.022 x 10 23 C atoms 1 mol Na = 6.022 x 10 23 Na atoms 1 mol Au= 6.022 x 10 23 Au atoms A Mole of Atoms

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A mole Of a covalent compound has Avogadro’s number of molecules 1 mol CO 2 = 6.022 x 10 23 CO 2 molecules 1 mol H 2 O = 6.022 x 10 23 H 2 O molecules Of an ionic compound contains Avogadro’s number of formula units 1 mol NaCl = 6.022 x 10 23 NaCl formula units 1 mol K 2 SO 4 = 6.022 x 10 23 K 2 SO 4 formula units A Mole of a Compound

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Samples of One-Mole Quantities

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Avogadro’s number 6.022 x 10 23 can be written as an equality and two conversion factors. Equality: 1 mol = 6.022 x 10 23 particles Conversion Factors: 6.022 x 10 23 particles and 1 mol 1 mol6.022 x 10 23 particles Avogadro’s Number

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Using Avogadro’s Number Avogadro’s number is used to convert Moles of a substance to Particles. How many Cu atoms are in 0.50 mol Cu? 0.50 mol Cu x 6.022 x 10 23 Cu atoms 1 mol Cu = 3.0 x 10 23 Cu atoms Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Using Avogadro’s Number Avogadro’s number is used to convert Particles of a substance to Moles. How many moles of CO 2 are in 2.50 x 10 24 CO 2 molecules? 2.50 x 10 24 CO 2 x 1 mol CO 2 6.022 x 10 23 CO 2 = 4.15 mol CO 2

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1. The number of atoms in 2.0 mol Al is A. 2.0 Al atoms B. 3.0 x 10 23 Al atoms C. 1.2 x 10 24 Al atoms 2. The number of moles of S in 1.8 x 10 24 atoms S is A. 1.0 mol S atoms B. 3.0 mol S atoms C. 1.1 x 10 48 mol S atoms Learning Check

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Subscripts and Moles The subscripts in a formula state The relationship of atoms in the formula. The moles of each element in 1 mol of compound. Glucose C 6 H 12 O 6 In 1 molecule: 6 atoms C 12 atoms H6 atoms O In 1 mol: 6 mol C 12 mol H 6 mol O

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Subscripts State Atoms and Moles The subscripts are used to write conversion factors for moles of each element in 1 mol compound. For aspirin C9H8O4, the following factors can be written: 9 mol C 8 mol H 4 mol O 1 mol C9H8O4 1 mol C9H8O4 1 mol C9H8O4 and 1 mol C9H8O4 1 mol C9H8O4 1 mol C9H8O4 9 mol C 8 mol H 4 mol O

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Learning Check How many O atoms are in 0.150 mol aspirin C 9 H 8 O 4 ?

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Molar Mass The molar mass Is the mass of one mole of an element or compound Is the atomic mass expressed in grams Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Molar Mass from Periodic Table Molar mass Is the atomic mass expressed in grams

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Molar Mass of a Compound The molar mass of a compound is the sum of the molar masses of the elements in the formula. Example: Calculate the molar mass of CaCl 2. ElementNumber of Moles Atomic MassTotal Mass Ca140.08 g/mol 40.08 g Cl235.45 g/mol 70.90 g CaCl 2 110.98 g

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Some One-Mole Quantities 32.07 g 55.85 g 58.44 g 294.20 g 342.30 g

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Prozac, C 17 H 18 F 3 NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.06 g/mol 2) 262.0 g/mol 3) 309.3 g/mol Learning Check

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Molar mass conversion factors: Are written from molar mass Relate grams and moles of an element or compound. Example: Write molar mass factors for methane CH 4 used in gas cook tops and gas heaters. Molar mass: 1 mol CH 4 = 16.04 g Conversion factors: 16.04 g CH 4 and 1 mol CH 4 1 mol CH 4 16.04 g CH 4 Molar Mass Factors

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Acetic acid C 2 H 4 O 2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid. Learning Check

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Molar mass factors are used to convert between the grams of a substance and the number of moles. Calculations Using Molar Mass Grams Molar mass factor Moles

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Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mol Al? Molar mass equality: 1 mol Al = 26.98 g Al Setup with molar mass as a factor: 3.00 mol Al x 26.98 g Al = 80.9 g Al 1 mol Al molar mass factor for Al Moles to Grams

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Learning Check Allyl sulfide C 6 H 10 S is a compound that has the odor of garlic. How many moles of C 6 H 10 S are in 225 g?

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Grams, Moles, and Particles A molar mass factor and Avogadro’s number convert: Grams to particles molar mass Avogadro’s number (g mol particles) Particles to grams Avogadro’s number molar mass (particles mol g)

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Learning Check How many H 2 O molecules are in 24.0 g H 2 O? 1) 4.52 x 10 23 2) 1.44 x 10 25 3) 8.02 x 10 23

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Percent Composition Percent composition Is the percent by mass of each element in a formula Example: Calculate the percent composition of CO 2. CO 2 = 1 C(12.01g) + 2 O(16.00 g) = 44.01 g/mol) 12.01 g C x 100 = 27.29 % C 44.01 g CO 2 32.00 g O x 100 = 72.71 % O 44.01 g CO 2 100.00 %

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Learning Check The chemical isoamyl acetate C 7 H 14 O 2 gives the odor of pears. What is the percent carbon in isoamyl acetate? 1) 7.102% C 2) 35.51% C 3) 64.58% C

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The molecular formula Is the true or actual number of the atoms in a molecule The empirical formula Is the simplest whole number ratio of the atoms Is calculated by dividing the subscripts in the molecular formula by a whole number to give the lowest ratio C 5 H 10 O 5 5 = C 1 H 2 O 1 = CH 2 O molecular empirical formula formula Types of Formulas

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Some Molecular and Empirical Formulas The molecular formula is the same or a multiple of the empirical.

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A. What is the empirical formula for C 4 H 8 ? 1) C 2 H 4 2) CH 2 3) CH B. What is the empirical formula for C 8 H 14 ? 1) C 4 H 7 2) C 6 H 12 3) C 8 H 14 C. Which is a possible molecular formula for CH 2 O? 1) C 4 H 4 O 4 2) C 2 H 4 O 2 3) C 3 H 6 O 3 Learning Check

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A compound contains 7.31 g Ni and 20.0 g Br. Calculate its empirical (simplest) formula. If the compound has a molar mass of 437 g/mol, calculate the molecular formula. Learning Check

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Aspirin is 60.0% C, 4.5% H and 35.5% O. Calculate its empirical (simplest) formula. Learning Check

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