1 The Mole 6.02 X 10 23 Everybody knows Avogadro’s Number

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The MoleThe Mole

6.02 X 6.02 X 10102323

• Everybody knows Avogadro’s Number

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STOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRY

- the study of the - the study of the quantitative quantitative aspects of aspects of chemical chemical reactions.reactions.

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The MoleThe Mole• A counting unit

• Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000

• 6.02 X 1023 (in scientific notation)

• This number is named in honor of Amedeo Avogadro (1776 – 1856)Amedeo Avogadro (1776 – 1856),

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The MoleThe Mole• 1 dozen cookies = 12 cookies• 1 mole of cookies = 6.02 X 1023 cookies

• 1 dozen cars = 12 cars• 1 mole of cars = 6.02 X 1023 cars

• 1 dozen Al atoms = 12 Al atoms• 1 mole of Al atoms = 6.02 X 1023 atoms

Note that the NUMBER is always the same, but the MASS is very different!

Mole is abbreviated mol: n = m/MM gmol-1

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= 6.02 x 1023 C atoms

= 6.02 x 1023 H2O molecules

= 6.02 x 1023 NaCl “molecules”

2 x 6.02 x 1023 ions

A Mole of ParticlesA Mole of Particles Contains 6.02 x 1023 particles

1 mole C

1 mole H2O

1 mole NaCl

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• Mole Ratio:

• http://www.files.chem.vt.edu/RVGS/ACT/notes/The_Mole.html

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n= m/MM the unit for MM isgmol-1

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Learning CheckLearning Check

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• The Mass of 1 mole (in grams)

• Equal to the numerical value of the average

atomic mass (get from periodic table)

1 mole of C atoms = 12.0 g

1 mole of Mg atoms = 24.3 g

1 mole of Cu atoms = 63.5 g

Molar MassMolar Mass

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Other Names Related to Molar MassOther Names Related to Molar Mass

• Molecular Mass/Molecular Weight: If you have a single

molecule, mass is measured in amu’s instead of grams. But,

the molecular mass/weight is the same numerical value as 1

mole of molecules. Only the units are different. (This is the

beauty of Avogadro’s Number!)

• Formula Mass/Formula Weight: Same goes for

compounds. But again, the numerical value is the same.

Only the units are different.

• THE POINT: You may hear all of these terms which mean the SAME NUMBER… just different units

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Find the molar mass

(usually we round to the tenths place)

Learning Check!Learning Check!

A.1 mole of Br atomsB.1 mole of Sn atoms

= 79.9 g/mole

= 118.7 g/mole

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Mass in grams of 1 mole equal numerically to the sum of the atomic masses

1 mole of CaCl2 = 111.1 g/mol

1 mole Ca x 40.1 g/mol

+ 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2

1 mole of N2O4 = 92.0 g/mol

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

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A. Molar Mass of K2O = ? Grams/mole

B. Molar Mass of antacid Al(OH)3 = ? Grams/mole


1515

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake

of serotonin by the brain. Find its molar

mass.

Learning CheckLearning Check

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molar mass

Grams Moles

Calculations with Molar MassCalculations with Molar Mass

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Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?

3.00 moles Al ? g Al

Converting Moles and GramsConverting Moles and Grams

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Answer = 81.0 g Al

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The artificial sweetener aspartame

(Nutra-Sweet) formula C14H18N2O5 is

used to sweeten diet foods, coffee and

soft drinks. How many moles of

aspartame are present in 225 g of

aspartame?


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Atoms/Molecules and GramsAtoms/Molecules and Grams

• Since 6.02 X 1023 particles = 1 mole AND

1 mole = molar mass (grams)• You can convert atoms/molecules to

moles and then moles to grams! (Two step process)

• You can’t go directly from atoms to grams!!!! You MUST go thru MOLES.

• That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

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molar mass Avogadro’s number Grams Moles particles

Everything must go through Moles!!!

CalculationsCalculations

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Atoms/Molecules and GramsAtoms/Molecules and Grams

How many atoms of Cu are present in 35.4 g of Cu?

= 3.4 X 1023 atoms Cu

2323


How many atoms of K are present in 78.4 g of K?

2424


What is the mass (in grams) of 1 molecule of glucose (C6H12O6)?

2525


How many atoms of O are present in 78.1 g of oxygen?

2626

Volume of GasesAvogadro’s Law

• http://www.chemistry.co.nz/avogadro.htm

27272 liters of CO gas react with 1 liter of O2 gas to

yield 2 liters of CO2 gas.

2 CO(g) + 1 O2(g) 2 CO2(g)

HOW CAN THIS BE POSSIBLE?

Avogadro's Law :

EQUAL VOLUMES OF DIFFERENT GASES CONTAIN EQUAL NUMBERS OF MOLECULES WHEN MEASURED AT THE SAME TERMPERATURE AND PRESSURE.

2828One mole of any gas occupies 22.41L at 0oC and 1 atm(stp) and contains the same number of particles - atoms - molecules.

22.41L is know as molar volume.

Molar Volume = 22.4 dm3 mol at s.t.p.

And

24.0 dm3 mol at r.t.p.

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1. What volume of carbon dioxide, measured at s.t.p. will be liberated from 5 g of

calcium carbonate, by the action of an excess of dilute hydrochloric acid?

2. 120 cm3 of hydrogen gas is released at S.T.P. when a small amount of Magnesium is

placed in excess dilute hydrochloric acid. What mass of Magnesium was added.

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Problems

• 1. Calculate the molar volume of each of the following:

a. 46.00 grams of nitrogen gas

b. 200.0 grams of carbon monoxide

c. 3.01 x 1023 molecules of ethane (C2H6)

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• If the amount of gas in a container is increased, the volume increases.

• If the amount of gas in a container is decreased, the volume decreases.

• V1/n1 = V2/n2

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• 5.00 L of a gas is known to contain 0.965 mol. If the amount of gas is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)?

Answer:

V1n2 = V2n1

(5.00 L) (1.80 mol) = (x) (0.965 mol)

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What is the percent carbon in C5H8NO4 (the

glutamic acid used to make MSG

(monosodium glutamate), a compound

used to flavor foods and tenderize meats?

a) 8.22 %C

b) 24.3 %C

c) 41.1 %C

Percent CompositionPercent Composition

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Chemical Formulas of Chemical Formulas of CompoundsCompounds

(HONORS only)(HONORS only)

• Formulas give the relative numbers of atoms or Formulas give the relative numbers of atoms or moles of each element in a formula unit - always moles of each element in a formula unit - always a whole number ratio (the law of definite a whole number ratio (the law of definite proportions).proportions).

NONO22 2 atoms of O for every 1 atom of N 2 atoms of O for every 1 atom of N

1 mole of NO1 mole of NO22 : 2 moles of O atoms to : 2 moles of O atoms to

every 1 mole of N atomsevery 1 mole of N atoms

• If we know or can determine the relative number If we know or can determine the relative number of moles of each element in a compound, we can of moles of each element in a compound, we can determine a formula for the compound.determine a formula for the compound.

3636Types of FormulasTypes of Formulas(HONORS only)(HONORS only)

• Empirical FormulaEmpirical Formula

The formula of a compound that The formula of a compound that expresses the expresses the smallest whole number smallest whole number ratioratio of the atoms present. of the atoms present.

Ionic formula are always empirical formulaIonic formula are always empirical formula

• Molecular FormulaMolecular Formula

The formula that states the The formula that states the actualactual number of each kind of atom found in number of each kind of atom found in one one moleculemolecule of the compound. of the compound.

3737To obtain an To obtain an Empirical Empirical Formula Formula (HONORS only)(HONORS only)

1.1. Determine the mass in grams of each Determine the mass in grams of each element present, if necessary.element present, if necessary.

2.2. Calculate the number of Calculate the number of molesmoles of of each each element.element.

3.3. Divide each by the smallest number of moles Divide each by the smallest number of moles to obtain the to obtain the simplest whole number ratio.simplest whole number ratio.

4.4. If whole numbers are not obtainedIf whole numbers are not obtained** in step in step 3), multiply through by the smallest number 3), multiply through by the smallest number that will give all whole numbersthat will give all whole numbers

** Be careful! Do not round off numbers prematurelyBe careful! Do not round off numbers prematurely

3838A sample of a brown gas, a major air pollutant, is A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a found to contain 2.34 g N and 5.34g O. Determine a formula for this substance.formula for this substance.

require require molemole ratios so convert grams to moles ratios so convert grams to moles

moles of N = moles of N = 2.34g of N 2.34g of N = 0.167 moles of N= 0.167 moles of N

14.01 g/mole14.01 g/mole

moles of O = moles of O = 5.34 g5.34 g = 0.334 moles of O = 0.334 moles of O

16.00 g/mole16.00 g/mole

Formula:Formula:

0.334 0.167ON 0.167 0.334 2

0.167 0.167

N O NO

(HONORS only)(HONORS only)

3939Calculation of the Molecular FormulaCalculation of the Molecular Formula(HONORS only)(HONORS only)

A compound has an empirical formula A compound has an empirical formula of NOof NO22. The colourless liquid, used in . The colourless liquid, used in

rocket engines has a molar mass of rocket engines has a molar mass of 92.0 g/mole. What is the 92.0 g/mole. What is the molecular molecular formula formula of this substance?of this substance?

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Empirical Formula from % Empirical Formula from % CompositionComposition (HONORS only)(HONORS only)

A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance?

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IB Problems

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Percent Composition Experiment• http://classes.mhcc.edu/enh/ch151_mr/pdf151/PercentKClO3.pdf

A student heated 100g of HgO according to

2 HgO => 2Hg + O2

and the remaining residue weighed 91.5g.

Find the percent error in the residue determination.

Given: mass of crucible=15g

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http://www.savitapall.com/matter/labs/Lab-Percentage%20Composition-MgO.pdfhttp://www2.ucdsb.on.ca/tiss/stretton/chem3/Lab_1_Percent_COmposition.html

http://www.chemistry.ucsc.edu/teaching/roland/Chem1M/procedures/1M_02_Empiricalproc.pdf

Documents

1 The Mole 6.02 X 10 23 Everybody knows Avogadro’s Number