Chapter 10

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Chapter 10Chemical Quantities
You will need a calculator for this chapter!
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Section 10.1 p. 287The Mole A Measurement
of Matter
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How do we measure items?

• You can measure mass,
• volume,
• or count pieces
• We measure mass in grams
• We measure volume in liters
• We count pieces in MOLES

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Other Ways to Measure Amount

• Pair 1 pair of socks 2 socks
• Dozen 1 dozen donuts 12 donuts
• Gross 1 gross of pencils 144 pencils (12
  dozen)
• Ream 1 ream of paper 500 sheets of paper
• Guided Practice Problem p. 289

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Practice Problem 2 pg. 289

• Assume 2.0 kg of apples is 1 dozen and that each
  apple has 8 seeds. How many apple seeds are in
  14 kg of apples? (work INDEPENDENTLY to solve)

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What is the mole?
Not this kind of mole!
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Moles (abbreviated mol)

• Derived from German word molekül (molecule)
• SI measurement of an amount
• 1 mole 6.02 x 1023 of representative
  particles, or..
• of carbon atoms in exactly 12 g of Carbon-12
  isotope
• Called Avogadros number

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What are Representative Particles?(Table 10.1 p.
290)

• The smallest pieces of a substance
• molecular cmpd - molecule
• ionic cmpd - formula unit (made of ions)
• element is the
• Remember the 7 diatomic elements? (made of
  molecules) BrINClHOF

atom
N2
I2
Br2
H2
O2
F2
Cl2
Guided Practice Problem 3 p. 291
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Mole Video 349
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Quick Quiz
6.02 x 1023

• How big is a mole?
• If everyone in the world got a mole of pennies,
  how much would every person have?
• If you stacked a mole of paper how many times
  would it go from the Earth to the moon?
• How long would it take for every person in the
  world to eat through a mole of marshmellows?

1 trillion bucks 1,000,000,000,000
80 billion times 80,000,000,000
40,000,000 years w/o a bathroom break!
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Consider these questions

• How many oxygen atoms in the following?
• CaCO3
• Al2(SO4)3
• How many ions in the following?
• CaCl2
• NaOH
• Al2(SO4)3

3 atoms of oxygen
12 (3 x 4) atoms of oxygen
3 total ions (1 Ca2 ion and 2 Cl1- ions)
2 total ions (1 Na1 ion and 1 OH1- ion)
5 total ions (2 Al3 3 SO42- ions)
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Practice problems
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The Mass of a Mole of an Element

• Atomic mass of element (mass of 1 atom) expressed
  in amu
• atomic masses - relative masses based on mass of
  C-12 (12.0 amu)
• 1 amu is 1/12 mass of C-12 atom

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Molar Mass.

• mass of 1 mol of element in grams (periodic
  table)
• 12.01 grams C has same particles as 1.01 g H
  55.85 g Fe
• 12.01 g C 1 mol C
• 1.01 g H 1 mol H
• 55.85 g Fe 1 mol Fe

All contain 6.02 x 1023 atoms
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Molar Mass Practice Problems
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What about compounds?

• 1 mol of H2O molecules has 2 mol of H atoms 1
  mol of O atoms (think of a compound as a molar
  ratio)
• To find mass of 1 mol of a cmpd
• determine moles of elements present
• Multiply times their mass (from periodic table)
• add up for total mass

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Calculating Molar Mass
Calculate molar mass of magnesium carbonate,
MgCO3.
84.3 g
24.3 g 12.0 g 3 x (16.00 g)

So, 84.3 g molar mass for MgCO3
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Section 10.2 p. 297Mole-Mass and
Mole-Volume Relationships
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Molar Mass

• Molar mass - generic term for mass of 1 mol of
  any substance (expressed in grams/mol)
• Same as
• 1) Gram Molecular Mass (for molecules)
  2) Gram Formula Mass (ionic compounds) 3)
  Gram Atomic Mass (for elements)
• molar mass is more broad term than these other
  specific masses

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Examples

• Calculate the molar mass of
• Na2S
• N2O4
• C
• Ca(NO3)2
• C6H12O6
• (NH4)3PO4

78.05 g/mol
92.02 g/mol
12.01 g/mol
164.10 g/mol
180.12 g/mol
149.12 g/mol
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Molar Mass is

• of g in 1 mol of atoms, formula units, or
  molecules
• Make conversion factors from these
• - To change btwn g of cmpd and mol of cmpd

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Using the Mole Roadmap

• How many moles is 5.69 g of NaOH?

0.142 mol NaOH
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The Mole-Volume Relationship

• gases
• - hard to determine mass
• how many moles of gas?
• 2 things affect gas V
• a) Temp b) Pressure
• compare all gases at temp pressure

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Standard Temperature and Pressure

• 0ºC 1 atm pressure
• - abbreviated STP
• At STP, 1 mol of any gas has V of 22.4 L
• - Called molar volume
• 1 mol of any gas at STP 22.4 L

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Practice Examples
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• Mole Day
• Celebrated on October 23rd from 602 am until
  602 pm
• (602 on 10-23)

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Density of a gas

• D m / V (density mass/volume)
• - for gas units are g / L
• find density of a gas at STP if formula known
• You need 1) mass and 2) volume
• Assume 1 mol, so mass is molar mass (from
  periodic table)
• At STP, V 22.4 L

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Practice Examples (Dm/V)
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Another way

• If given density, find molar mass of gas
• Assume 1 mol at STP, so V 22.4 L
• modify D m/V to show
• m will be mass of 1 mol, given 22.4 L
• What is molar mass of a gas with density of
  1.964 g/L?
• How about a density of 2.86 g/L?

m D x V
44.0 g/mol
64.0 g/mol
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Summary

• all equal
• a) 1 mole
• b) molar mass (in grams/mol)
• c) 6.02 x 1023 representative particles (atoms,
  molecules, or formula units)
• d) 22.4 L of gas at STP
• make conversion factors from these 4 values
  (p.303)

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Notice all conversions must go through the MOLE!
Copy this conversion map into your notes!
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Section 10.3p. 305Percent Composition and
Chemical Formulas
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• All percent problems
• part
• whole
• Find mass of each element,
• Divide by total mass of cmpd x 100

x 100 percent
mass of element
mass of element
x 100
mass of cmpd
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composition from mass

• Calculate the percent composition of a compound
  that is made of 29.0 grams of Ag with 4.30 grams
  of S.

29.0 g Ag
X 100 87.1 Ag
33.3 g total
Total 100
4.30 g S
X 100 12.9 S
33.3 g total
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comp from the chemical formula

• If we know formula, assume you have 1 mole,
• Subscripts used to calculate mass of each element
  in 1 mole of cmpd
• sum of masses is molar mass

Mass of element in 1 mol cmpd
x 100
mass
Molar mass of cmpd
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Composition Examples
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composition as conversion factor

• We can also use as conversion factor to
  calculate grams of element in cmpd
• Calculate C in C3H8
• What is mass of C in 82.0 g sample of propane
  (C3H8)

67.1 g C
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Composition

• 415

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What is an Empirical Formula?

• Like ingredients for recipe double recipe, you
  double each ingredient, but ratio of ingredients
  stays same
• Empirical formula lowest whole number ratio of
  atoms in cmpd

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Calculating Empirical

• Find lowest whole number ratio
• C6H12O6
• CH4N
• A formula is not just ratio of atoms, it is also
  ratio of moles
• 1 molecule of CO2 1 atom of C and 2 atoms of O
• 1 mol of CO2 1 mol C and 2 mol O

CH2O
this is already the lowest ratio.
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Calculating Empirical

• get a ratio from composition
• Assume you have a 100 g sample
• - the percentage become grams (75.1 75.1
  grams)
• Convert grams to moles.
• Find lowest whole number ratio by dividing each
  of moles by smallest value

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Example

• Calculate empirical formula of cmpd composed of
  38.67 C, 16.22 H, and 45.11 N.
• Assume 100 g sample, so
• 38.67 g C x 1mol C 3.22 mole C
  12.0 g C
• 16.22 g H x 1mol H 16.22 mole H
  1.0 g H
• 45.11 g N x 1mol N 3.22 mole N
  14.0 g N

CH5N
Now divide each value by the smallest value
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Example

• The ratio is 3.22 mol C 1 mol C
  3.22 mol N 1 mol N
• The ratio is 16.22 mol H 5 mol H
  3.22 mol N 1 mol N
• C1H5N1 which is CH5N

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Practice Problem 36 p. 310
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What is a Molecular Formula?

• Molecular formula true of atoms of each
  element in formula of cmpd
• molecular cmpds only
• Example molecular formula for benzene is C6H6
  (note that everything is divisible by 6)
• Therefore, empirical formula CH (the lowest
  whole number ratio)

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Formulas (continued)
ionic compounds ALWAYS empirical (cannot be
reduced).
Examples
NaCl
MgCl2
Al2(SO4)3
K2CO3
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Formulas (continued)
Formulas for molecular compounds MIGHT be
empirical (lowest whole number ratio).
Molecular
C6H12O6
C12H22O11
H2O
(Correct formula)
Empirical
H2O
CH2O
C12H22O11
(Lowest whole number ratio)
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Empirical to molecular

• Since empirical formula is lowest ratio, the
  actual molecule weighs more

Molar mass
whole to increase each coefficient in empirical
formula

Empirical formula mass
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Empirical to molecular practice problem
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Empirical and Molecular Formulas

• 329