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

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

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

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

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

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

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

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

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 amu = amu Formula mass 1 Na 2 SO 4 1 S x amu = amu amu 1 S 4 O x amu = amu 1 O

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

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

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

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

Samples of One-Mole Quantities

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

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 x Cu atoms 1 mol Cu = 3.0 x Cu atoms Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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 CO 2 molecules? 2.50 x CO 2 x 1 mol CO x CO 2 = 4.15 mol CO 2

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

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

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

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

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

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

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 Ca g/mol g Cl g/mol g CaCl g

Some One-Mole Quantities g g g g g

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) g/mol 2) g/mol 3) g/mol Learning Check

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 = g Conversion factors: g CH 4 and 1 mol CH 4 1 mol CH g CH 4 Molar Mass Factors

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

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

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 = g Al Setup with molar mass as a factor: 3.00 mol Al x g Al = 80.9 g Al 1 mol Al molar mass factor for Al Moles to Grams

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?

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)

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

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) = g/mol) g C x 100 = % C g CO g O x 100 = % O g CO %

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

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

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

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

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

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