11

The MoleThe Mole

6.02 X 6.02 X 10102323

22

Average atomic Masses

• Atomic masses on the Periodic Table are not whole numbers since they are weighted averages of Mass Numbers (P+N)

• Average atomic mass depends on two factors- mass and relative abundance of each isotope.

• Example- Cu-63 (69.17% and 62.94amu) and Cu-65(30.83% and 64.93amu)

- Average atomic mass= (69.17x62.94)+(30.83x64.93) divided by 100=63.55amu

- Do Practice Q1-2, p133.

33

STOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRY

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

44

Launch lab p 319- How much is a mole?

• Decades or dozens are counting units. The Mole is also a counting unit.

• Measure a small item (paperclip, eraser, penny) in cm using a ruler.

• If a mole is 6.02 X1023 items, how far will a mole of your items, placed end-to-end lengthwise, extend into space? Express your answer in meters.

• Convert this answer into light years (ly).

• (1 ly=9.46 X1015 m).

55

How much is a mole?

• Compare the distance you calculated with these astronomical distances:

• Distance to the nearest star (other than the sun)=4.3 ly

• Distance to the center of the galaxy= 30,000 ly

• Distance to the nearest galaxy=2X106 ly

66

The MoleThe Mole

• A counting unit• Similar to a dozen or gross, 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 (termed Avogadro’s

number) is named in honor of Amedeo Amedeo Avogadro (1776 – 1856)Avogadro (1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present

77

Just How Big is a Mole?Just How Big is a Mole?

• Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.

• If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

88

The MoleThe Mole

･ Atoms and molecules are extremely small making it very difficult to measure their masses individually. ﾐIt is easier to weigh a large collection of these. ･ A mole (abbreviated as mol) is defined as the number of C atoms in exactly 12 grams of pure C-12.

･ This number is called Avogadro’s number.

99

= 6.02 x 1023 C atoms

= 6.02 x 1023 H2O molecules

= 6.02 x 1023 NaCl “molecules”(technically, ionics are compounds not

molecules so they are called formula units)

6.02 x 1023 Na+ ions and

6.02 x 1023 Cl– ions

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

1 mole C

1 mole H2O

1 mole NaCl

1010

6.02 x 1023 particles

1 mole

or

1 mole

6.02 x 1023 particles

Note that a particle could be an atom OR a molecule!

Avogadro’s Number as Avogadro’s Number as Conversion FactorConversion Factor

1111

1. Number of atoms in 0.500 mole of Ala) 500 Al atoms

b) 6.02 x 1023 Al atomsc) 3.01 x 1023 Al atoms

2.Number of moles of S in 1.8 x 1024 S atomsa) 1.0 mole S atomsb) 3.0 mole S atomsc) 1.1 x 1048 mole S atoms

Learning CheckLearning Check

1212

･ The mass in grams of one mole of atoms of any pure substance is known as its molar mass. The unit used is g/mol (gmol-1).

･ Molar mass of sodium (Na) = mass of exactly one mole of Na atoms = 22.99 g/mol = mass of 6.022 x 1023atoms of Na.

･ Molar mass of Uranium (U) = 238.03 g/mol. ･ The atomic mass number of an element in a periodic table = molar mass for the element

Molar MassMolar Mass

1313

Practice p 322

• Determine the number of Zn atoms in 2.5 mol of Zn.

• Calculate the number of molecules in 11.5 mol of water (H2O).

• How many molecules of AgNO3 are there in 3.25 mol of it?

• Calculate the number of oxygen atoms in 5 mol of oxygen molecules.

1414

Practice p 324

• How many moles contain each of the following?

• 5.75 X 1024 atoms Al• 2.50 X 1020 atoms Fe• How many moles contain each of the following molecules?

• 3.75 X 1024 CO2

• 3.58 X 1023 ZnCl2

1515

Practice p 328• Determine the mass in grams of each of the following

• 3.57 mol Al• 42.6 mol Si• Convert each given quantity in scientific notation to mass in grams expressed in scientific notation

• 3.45 X 102 mol Co• 2.45 X 10-2 mol Zn

1616

Practice p 329• Determine the number of moles in each of the following

• 25.5 g Ag• 300 g S• Convert each mass to moles. Express the answer in scientific notation.

• 1.25 X 103 g Zn • 1 kg Fe

1717

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

1818

･ 1 mole of any compound = 6.022 x 1023units of the compound. ･ Molar masses of compounds are calculated by adding the molar masses of the atoms present in the compound.

･ Calculate the molar mass of Ca3(PO4)2

--Need to look the molar masses of each of the element present and multiply by the number of the atoms present.

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

1919

A. Molar Mass of K2O = ? Grams/mole

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

Learning Check!Learning Check!

2020Practice p 335 (bottom)•Determine the molar mass

of each ionic compound-

•NaOH, CaCl2, KC2H3O2

•Calculate the molar mass of each molecular compound- C2H5OH, HCN, CCl4

•Sr(NO3)2, (NH4)3PO4, C12H22O11

2121

Practice p 335 (top)• Determine the moles of Cl- ions in 2.5 moles of ZnCl2.

• Calculate the number of moles of each element in 1.25 mol C6H12O6.

• Determine the number of moles of sulfate ions present in 3 mol of Fe2(SO4)3.

• How many moles of oxygen atoms are present in 5 mol of P2O5?

• Calculate the number of moles of hydrogen atoms in 1.15 X101 mol of water. Express the answer in scientific notation.

2222

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake

of serotonin by the brain. Find its molar

mass.

Learning CheckLearning Check

2323

molar mass

Grams Moles

Calculations with Molar MassCalculations with Molar Mass

2424

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

2525

1. Molar mass of Al 1 mole Al = 27.0 g Al

2. Conversion factors for Al

27.0g Al or 1 mol Al

1 mol Al 27.0 g Al

3. Setup 3.00 moles Al x 27.0 g Al

1 mole Al

Answer = 81.0 g Al

2626

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?

Learning Check!Learning Check!

2727

Practice p 336

• What is the mass of 3.25 mol of H2SO4?

• What is the mass of 4.35 X 101 mol of ZnCl2?

• Write the chemical formula for potassium permanganate, and then calculate the mass in grams of 2.55 mol of the compound.

2828

Practice p 337

• Determine the number of moles present in each compound-22.6 g AgNO3, 6.5 g ZnSO4, 35.0 g HCl.

• Identify each as an ionic and molecular compound and convert the given mass to moles. Express your answers in scientific notation- 2.5 kg Fe2O3, 25.4 mg PbCl4.

2929

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!

3030

molar mass Avogadro’s number Grams Moles particles

Everything must go through Moles!!!

CalculationsCalculations

3131

Atoms/Molecules and GramsAtoms/Molecules and Grams

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

35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu

= 3.4 X 1023 atoms Cu

3232

Learning Check!Learning Check!

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

3333

Learning Check!Learning Check!

What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?

3434

Learning Check!Learning Check!

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

78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2

3535

Practice p 339• A sample of ethanol C2H5OH has a mass of 45.6 g.- How many C atoms does the sample contain? How many H atoms are present? How many O atoms are present?

• A sample of Na2SO3 has a mass of 2.25 g.- How many Na+ ions are present? How many SO3

2-ions are present?What is the mass in grams of one molecule of Na2SO3?

3636

Contd-• A sample of CO2 has a mass of 52 g.- How many C atoms are present? How many O atoms are present? What is the mass in grams of 1 molecule of CO2?

• A sample of silver chromate has a mass of 25.8 g.- Write the formula for silver chromate. How many cations are present? How many anions are present? What is the mass in grams of 1 molecule of silver chromate?

3737

Percent Composition of Compounds

• Composition of compounds can be described in 2 ways: By the number of its constituent atoms. By the mass (%) of each element present.

• ･ The mass percents of elements are obtained by comparing the mass of each element present in 1 mole of the compound to the total mass of the compound.

• ･ Useful today with unknown compounds.

3838

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

3939

Practice p 344• What is the percent composition of H3PO4?

• Which has the larger percent by mass of sulfur H2SO3 or H2S2O8?

• Calculate the percent by mass of each element in CaCl2.

• Sodium sulfate is used in the manufacture of detergents- Identify each of the elements of sodium sulfate, and write the formula. - identify the compound as ionic or covalent- calculate the percent by mass of each element in sodium sulfate.

4040

Chemical Formulas of Chemical Formulas of CompoundsCompounds

• 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.

4141Types of FormulasTypes of Formulas

• Empirical FormulaEmpirical FormulaThe formula of a compound that The formula of a compound that

expresses the expresses the smallest whole number ratiosmallest whole number ratio of the atoms present.of the atoms present.

((Ionic formulae are always empirical formulae)Ionic formulae are always empirical formulae)

• Molecular FormulaMolecular FormulaThe 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. Example- CH is of the compound. Example- CH is the empirical formula for benzene, C6H6).the empirical formula for benzene, C6H6).

4242To obtain an To obtain an Empirical Empirical Formula Formula

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

4343A 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=

4444

Calculation of the Molecular Calculation of the Molecular FormulaFormula

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?

4545

Empirical Formula from % Empirical Formula from % CompositionComposition

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?

4646

Practice p 346• A compound has 63.16% O and 36.84%N. What is the empirical formula of this compound?

• Determine the empirical formula of a compound containing 35.98% Al and 64.02%S.

• Propane contains 81.82% C and 18.18% H. What is the empirical formula ?

• Aspirin has 60% C, 4.44% H, and 35.56% O. Determine the empirical formula of this compound.

4747

Practice p 350• A compound has 49.98 g C and 10.47g H. It’s Molar mass is 58.12g. Determine it’s molecular formula.

• A liquid has 46.68% N and 53.32% O, molar mass is 60.01g. What is the molecular formula?

• An oxide of potassium has 19.55g K and 4 g of O. What is it’s empirical formula?

• A compound has 65.45 % C, 5.45%H and 29.09% O. If the molar mass is 110g, what is its molecular formula?

• Morphine has 17.9g C, 1.68g H, 4.225g O and 1.228 g N. Determine the empirical formula of morphine.

4848

Formulas of hydrates

• Hydrate is a compound with a fixed number of water molecules bound to it.

• Na2CO3.10H2O- sodium carbonate decahydrate

• Hydrate+ heat= anhydrous compound (without water)

4949

How to find out the formula of a hydrate

• Need to know how many moles of H20 attached to the molecule- BaCl2.xH2O

• Mass sample• Heat it, mass again. • The difference in mass= mass of water• Divide it by molar mass of H20 (18g)= moles of water

• Determine moles of compound as well.• Determine ratio of water molecules to compound molecules.

5050

Try it!

• A mass of 2.5 g of blue, hydrated copper sulfate (CuSO4.xH2O) is placed in a crucible and heated. After heating, 1.59 g of white anhydrous copper sulfate (CuSO4) remains. What is the formula for the hydrate?

5151

Practice p 353• A hydrate has 48.8% MgSO4 and 51.2% H2O. What is its formula and name?

• An 11.75 g sample of a common hydrate of cobalt (II) chloride is heated. After heating, 0.0712 mol of anhydrous cobalt chloride remains. What is the formula and name of this hydrate?

• P354 q81- Arrange these hydrates in order of increasing percent water content- MgSO4.7H2O, Ba(OH)2.8H2O, CoCl2.6H2O