Chapter 10Chapter 10“Chemical Quantities”“Chemical Quantities”

You will need a calculator for this

chapter!

Section 10.1 p. 287Section 10.1 p. 287The Mole: A Measurement The Mole: A Measurement

of Matterof Matter

How do we measure items?How do we measure items?You can measure mass, volume,or count pieces

We measure mass in gramsWe measure volume in litersWe count pieces in MOLES

Other Ways to Measure Other Ways to Measure AmountAmount

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 paperGuided Practice Problem p. 289

Practice Problem #2 Practice Problem #2 pg. 289pg. 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)

What is the mole?

Not this kind of mole!

Moles (abbreviated Moles (abbreviated molmol))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 Avogadro’s numberAvogadro’s number

What are Representative Particles?What are Representative Particles?

(Table 10.1 p. 290)(Table 10.1 p. 290) The smallest pieces of a

substance:1) molecular cmpd - molecule2) ionic cmpd - formula unit (made

of ions)3) element: is the

• Remember the 7 diatomic elements? (made of molecules) BrINClHOFH2

N2 O2 F2Cl2

I2Br2

atoatomm

Guided Practice Problem #3 p. 291

Mole Video 3:49

Quick QuizQuick Quiz• 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?

6.02 x 6.02 x 10102323

1 trillion bucks1 trillion bucks$1,000,000,000,000$1,000,000,000,000

80 billion 80 billion timestimes80,000,000,00080,000,000,000

40,000,000 years w/o 40,000,000 years w/o a bathroom break!a bathroom break!

Consider these questions:Consider these questions:• How many oxygen atoms in

the following?CaCO3

Al2(SO4)3

• How many ions in the following?CaCl2NaOHAl2(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)

Practice problemsPractice problems

The Mass of a Mole of an The Mass of a Mole of an ElementElement

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

Molar Mass…. Molar Mass…. = mass of 1 mol of element in in

gramsgrams (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 All contain contain 6.02 x 6.02 x 10102323 atomsatoms

Molar Mass Practice Molar Mass Practice ProblemsProblems

What about compounds?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: odetermine # moles of elements presentoMultiply # times their mass (from periodic table)oadd up for total mass

Calculating Molar MassCalculating Molar Mass

Calculate molar mass of magnesium carbonate, MgCO3.

24.3 g + 12.0 g + 3 x (16.00 g) = 84.3 g

So, 84.3 g = molar mass for MgCO3

Section 10.2 Section 10.2 p. 297p. 297

Mole-Mass and Mole-Mole-Mass and Mole-Volume RelationshipsVolume Relationships

Molar MassMolar MassMolar 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)

o molar mass is more broad term than these other specific masses

ExamplesExamples 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

Molar Mass is…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

Using the Mole RoadmapUsing the Mole RoadmapHow many moles is 5.69 g of NaOH?0.142 mol NaOH

The Mole-Volume RelationshipThe Mole-Volume Relationshipgases

- hard to determine masshow many moles of gas?2 things affect gas V:

a) Temp & b) Pressurecompare all gases at = temp & pressure

Standard Temperature and PressureStandard Temperature and Pressure 0ºC & 1 atm pressure

- abbreviated “STP” At STP, 1 mol of anyany gas has V of 22.4 L- Called molar volume

1 mol of any gas at STP = 22.4 L

Practice ExamplesPractice Examples

Mole DayCelebrated on October 23rd from 6:02 am until 6:02 pm(6:02 on 10-23)

Density of a gasDensity 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

Practice Examples Practice Examples (D=m/V)(D=m/V)

Another way:Another way: If given densityIf 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?

= 44.0 g/mol

64.0 g/mol

m = D x V

SummarySummary• all equal:all equal:

a) 1 moleb) molar mass (in grams/mol)c) 6.02 x 1023 representative particles (atoms, molecules, or formula units)

d) 22.4 L of gas at STPmake conversion factors from these 4 values (p.303)

Notice all conversions Notice all conversions must go through the must go through the

MOLE!MOLE!Copy this conversion Copy this conversion map into your notes!map into your notes!

Section 10.3Section 10.3p. 305p. 305

Percent Composition Percent Composition and Chemical and Chemical

FormulasFormulas

All percent problems: part whole

1)1) Find mass of each element,Find mass of each element,

2)2) Divide by total mass of cmpd; & x Divide by total mass of cmpd; & x 100100

x 100 % = percent

%mass of element = mass of element

x 100% mass of cmpd

% composition from mass% 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 Ag33.3 g total

X 100 = 87.1 % Ag

4.30 g S33.3 g total

X 100 = 12.9 % S

Total = 100 %

% comp from the chemical formula% 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

% Composition Examples% Composition Examples

% composition as % composition as conversion factorconversion factor

We can also use % as conversion factor conversion factor to calculate # grams of element in cmpd

Calculate % C in Calculate % C in C3H8

What is mass of C in 82.0 g sample of propane (C3H8)

67.1 g C

% Composition% Composition4:15

What is an Empirical Formula?What is an Empirical Formula?• Like ingredients for recipe –

double recipe, you double each ingredient, but ratioratio of ingredients stays same

• Empirical formula: lowest whole number ratio of atoms in cmpd

Calculating EmpiricalCalculating EmpiricalFind lowest whole number ratio

C6H12O6

CH4NA formula is not just ratio of

atomsatoms, it is also ratio of moles1 moleculemolecule of CO2 = 1 atom of C atom of C and 2 atoms of O 2 atoms of O

1 mol of CO2 = 1 mol C and 2 mol O

= CH2O

= this is already the lowest ratio.

Calculating EmpiricalCalculating Empirical get a ratio from % composition1)Assume you have a 100 g

sample- the percentagepercentage become gramsgrams (75.1%75.1% = 75.1 75.1

gramsgrams)

2) Convert gramsgrams to molesmoles. 3) Find lowest whole number ratio

by dividing each # of molesmoles by smallest value

ExampleExampleCalculate 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

Now divide each value by the smallest value

CH5N

ExampleExample 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

Practice Problem 36 p. 310Practice Problem 36 p. 310

What is a Molecular Formula?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)

FormulasFormulas (continued)(continued)

ionic compoundsionic compounds ALWAYS empirical (cannot be reduced).

Examples:

NaCl MgCl2 Al2(SO4)3 K2CO3

FormulasFormulas (continued)(continued)

Formulas for molecular compoundsmolecular compounds

MIGHT be empirical (lowest whole number ratio).

Molecular:

H2O

C6H12O6 C12H22O11

Empirical:

H2O

CH2O C12H22O11

(Correct formula)

(Lowest whole number ratio)

Empirical to molecularEmpirical to molecularSince empirical formula is lowest ratio, the actual molecule weighs more

Molar mass

Empirical formula masswhole # to increase each coefficient in empirical formula

=

Empirical to molecular Empirical to molecular practice problempractice problem

Empirical and Empirical and Molecular FormulasMolecular Formulas

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