The MoleThe MoleChapter 11Chapter 11

Measuring MatterMeasuring MatterSection 11.1Section 11.1

Chemists need a convenient method Chemists need a convenient method for counting the number of atoms, for counting the number of atoms, molecules or formula units in a molecules or formula units in a sample of a substance. sample of a substance.

Atoms and molecules are so small Atoms and molecules are so small that chemists created their own that chemists created their own counting unit called the counting unit called the molemole

What is a mole? What is a mole?

MoleMole- abbreviated mol is the SI base - abbreviated mol is the SI base unit used to unit used to measure the amount of a measure the amount of a substance substance

A mole of A mole of anythinganything contains contains 6.02 x106.02 x102323 representative particlesrepresentative particles

602 000 000 000 000 000 000 000602 000 000 000 000 000 000 000 This number is known as This number is known as Avogadro’s Avogadro’s

numbernumber

Conversion FactorsConversion Factors Recall from chapter Recall from chapter

2:2: A method of problem solving that focuses A method of problem solving that focuses on the units to describe matteron the units to describe matter Conversion factor-Conversion factor- a a ratioratio of equivalent of equivalent

values used to express the same quantity in values used to express the same quantity in different unitsdifferent units

Example: 4800g to kgExample: 4800g to kgConversion factor: 1000g= Conversion factor: 1000g= 1kg1kg kg 48

1000g

kg 1 x g 4800

One mole = 6.02 x10One mole = 6.02 x102323 representative representative particles particles

Conversion factor: Conversion factor:

# particles# particles = # of moles x = # of moles x

mole

particles tiverepresenta

1

1002.6 23x

mole

particles tiverepresenta

1

1002.6 23x

PracticePractice Determine the number of atoms in Determine the number of atoms in

2.50 mol of Zn. 2.50 mol of Zn.

Calculate the number of molecules in Calculate the number of molecules in 11.5 mol H11.5 mol H22O. O.

How many molesHow many moles contain each of the contain each of the following:following: 5.75 x105.75 x102424 atoms Al atoms Al

3.58 x103.58 x102323 formula units of ZnCl formula units of ZnCl22

Mass and the MoleMass and the MoleSection 11.2Section 11.2

Molar Mass-Molar Mass- The mass The mass in gramsin grams of of one moleone mole of any pure substance of any pure substance Units: grams/mol Units: grams/mol Example: Manganese has an atomic Example: Manganese has an atomic

mass of 54.94 amu there fore it has a mass of 54.94 amu there fore it has a molar mass of 54.94 g/molmolar mass of 54.94 g/mol

Suppose you are in a chemistry lab Suppose you are in a chemistry lab and you need 3.00 moles of and you need 3.00 moles of manganese. What amount would you manganese. What amount would you weigh out on the scale? weigh out on the scale? What information do I need to know? What information do I need to know? What information is given in the What information is given in the

problem? problem?

Determine the mass in Determine the mass in grams:grams:

3.57 mol Al3.57 mol Al

2.45 mol Zn2.45 mol Zn

42.6 mol Si42.6 mol Si

Atoms or Molecules MOLES Grams

Convert using 6.02 x1023 Convert using

molar mass

How many atoms are in each How many atoms are in each of the following samples?of the following samples?

55.2 g Li55.2 g Li

0.120 kg Ti0.120 kg Ti

Moles to CompoundsMoles to CompoundsSection 11.3Section 11.3

Recall that the chemical formula of a Recall that the chemical formula of a compound indicates the types of compound indicates the types of atoms and the number of each atoms and the number of each contained in one formula unit of the contained in one formula unit of the compoundcompound Example: CClExample: CCl22FF2 2 (Freon) (Freon)

1 carbon1 carbon 2 chlorine2 chlorine 2 fluorine 2 fluorine

Determine the number of moles of Determine the number of moles of chloride ions in 2.50 mol ZnClchloride ions in 2.50 mol ZnCl22

What information is given in the What information is given in the problem? problem?

2.50 mol ZnCl2.50 mol ZnCl22

2 mol Cl2 mol Cl-- ions : 1 mol ZnCl ions : 1 mol ZnCl22

Practice ProblemPractice Problem How many moles of oxygen atoms How many moles of oxygen atoms

are present in 5.00 mol diphosphorus are present in 5.00 mol diphosphorus pentoxide? pentoxide?

The Molar Mass of The Molar Mass of CompoundsCompounds

Molar mass of a compound is determined by Molar mass of a compound is determined by addingadding the masses of all elements present. the masses of all elements present.

# of moles x molar mass = number of grams# of moles x molar mass = number of grams Example: KExample: K22CrOCrO44

2 mol K x 2 mol K x 39.10 g K 39.10 g K = 78.20 g = 78.20 g

1 mol K 1 mol K

1 mol Cr x 1 mol Cr x 52.00 g Cr52.00 g Cr = 52.00 g = 52.00 g

1 mol Cr1 mol Cr

4 mol O x 4 mol O x 16.00 g O16.00 g O = 64.00 g = 64.00 g

1 mol O1 mol O

78.20 g

52.00 g

+ 64.00 g

194.20 g K2CrO4

Practice ProblemsPractice Problems

Determine the molar mass of each of Determine the molar mass of each of the following compounds:the following compounds: NaOHNaOH Sr(NOSr(NO33))22

(NH(NH44)PO)PO44

CC1212HH2222OO1111

CC22HH55OHOH

Answers Answers

Determine the molar mass of each of Determine the molar mass of each of the following compounds:the following compounds: NaOHNaOH 40.00 g/mol NaOH40.00 g/mol NaOH Sr(NOSr(NO33))2 2 211.64 g/mol Sr(NO211.64 g/mol Sr(NO33))22

(NH(NH44)PO)PO4 4 149.10 g/mol (NH149.10 g/mol (NH44)PO)PO44

CC1212HH2222OO1111 342.30 g/mol C342.30 g/mol C1212HH2222OO1111

CC22HH55OH OH 46.07 g/mol C46.07 g/mol C22HH55OHOH

Mole- to- Mass ConversionMole- to- Mass Conversion

Atoms or Molecules MOLES Grams

Convert using 6.02 x1023 Convert using

molar mass

ExampleExample What is the mass of 3.25 moles of What is the mass of 3.25 moles of

sulfuric acid (Hsulfuric acid (H22SOSO44)? )? What am I given in the problem? What am I given in the problem? What do I need to know?What do I need to know?

Atoms or Molecules MOLES Grams

Convert using 6.02 x1023 Convert using

molar mass

3.25 mol3.25 mol HH22SOSO44

3.25 mol3.25 mol HH22SOSO4 4

Determine the number of moles present in Determine the number of moles present in 22.6 g AgNO22.6 g AgNO33

Converting the mass of a Converting the mass of a compound to number of compound to number of

particlesparticlesAtoms or Molecules MOLES Grams

Convert using 6.02 x1023 Convert using

molar mass

Practice ProblemPractice Problem

A sample of silver chromate (AgCrOA sample of silver chromate (AgCrO44) ) has a mass of 25.8g.has a mass of 25.8g. How many AgHow many Ag++ ions are present? ions are present? How many CrOHow many CrO44 2-2- ions are present? ions are present? What is the mass in grams of one What is the mass in grams of one

formula unit of silver chromate? formula unit of silver chromate?

How many AgHow many Ag++ ions are present? ions are present?

How many CrOHow many CrO44 2-2- ions are present? ions are present?

What is the mass in grams of one formula unit What is the mass in grams of one formula unit of silver chromate? of silver chromate?

Empirical and Molecular Empirical and Molecular FormulasFormulas

Section 11.4Section 11.4 The percent by mass of each element The percent by mass of each element

in a compound is called the in a compound is called the percent percent compositioncomposition of a compound of a compound

mass of elementmass of element x 100 = x 100 = percent bypercent by mass of compoundmass of compound mass mass

Practice ProblemPractice Problem Calculate the percent composition of Calculate the percent composition of

baking soda (NaHCObaking soda (NaHCO33) ) (Molar Mass= 84 (Molar Mass= 84

g/mol)g/mol) NaNa

HH

CC

OO

Which has the larger percent of Which has the larger percent of sulfur, Hsulfur, H22SOSO33 or H or H22SS22OO88? ?

Empirical FormulaEmpirical Formula Empirical Formula-Empirical Formula- formula with the formula with the

smallest whole number mole ratio of smallest whole number mole ratio of the elements the elements

1.1. Starting with the percent composition- drop the Starting with the percent composition- drop the percentage sign and replace it with gramspercentage sign and replace it with grams

2.2. Multiply the mass of each element by the Multiply the mass of each element by the conversion factor that relates moles to grams conversion factor that relates moles to grams (molar mass)(molar mass)

3.3. Calculate the simplest whole number ratio of Calculate the simplest whole number ratio of moles of the elements by dividing each number moles of the elements by dividing each number of moles by the smallest value in the mole ratio. of moles by the smallest value in the mole ratio. If a fraction is present- multiply by 2 to If a fraction is present- multiply by 2 to

produce a whole numberproduce a whole number

Practice ProblemPractice Problem Determine the empirical formula for a compound Determine the empirical formula for a compound

that contains 35.98% aluminum and 64.02% that contains 35.98% aluminum and 64.02% sulfur. sulfur.

Molecular FormulaMolecular Formula Molecular Formula-Molecular Formula- specifies the actual specifies the actual

number of atoms of each element in one number of atoms of each element in one molecule or formula unit of the substancemolecule or formula unit of the substance

experimentally determined molar mass experimentally determined molar mass = = nnmass of empirical formula mass of empirical formula

Molecular formula = (empirical formula) Molecular formula = (empirical formula) nn

Practice ProblemPractice Problem

A colorless liquid composed of 46.68% nitrogen A colorless liquid composed of 46.68% nitrogen

and 53.32% oxygen has a molar mass of 60.01 and 53.32% oxygen has a molar mass of 60.01

g/mol. What is the molecular formula?g/mol. What is the molecular formula?

The Formula of a HydrateThe Formula of a HydrateSection 11.5Section 11.5

A A hydratehydrate is a is a compound that has compound that has a specific number of a specific number of water molecules water molecules bound to its atoms. bound to its atoms.

The number of The number of water molecules water molecules bound to its atoms bound to its atoms is indicated with a is indicated with a prefixprefix

Prefixes in Prefixes in HydratesHydrates

NumbeNumber of r of

AtomsAtoms

PrefixPrefix NumbeNumber of r of

AtomsAtoms

PrefixPrefix

11 Mono- 6 Hexa-

22 Di- 7 Hepta-

33 Tri- 8 Octa-

44 Tetra- 9 Nona-

55 Penta- 10 Deca-

Determining the formula of a Determining the formula of a hydratehydrate

A mass of 2.50 g of blue, hydrated copper sulfate (CuSOA mass of 2.50 g of blue, hydrated copper sulfate (CuSO44

··x x HH22O) is placed in a crucible and heated. After O) is placed in a crucible and heated. After

heating, 1.59g white anhydrous copper sulfate heating, 1.59g white anhydrous copper sulfate (CuSO(CuSO44) remains. ) remains.

What is the formula for the hydrate? Name the hydrate.What is the formula for the hydrate? Name the hydrate.

Known: Known: Mass of hydrated compound: 2.50 g CuSOMass of hydrated compound: 2.50 g CuSO44 ··x x HH22O O Mass of anhydrous compound: 1.59 g CuSOMass of anhydrous compound: 1.59 g CuSO44

Molar mass of CuSOMolar mass of CuSO44: 159.6 g/mol CuSO: 159.6 g/mol CuSO44

Molar mass of HMolar mass of H22O: 18.02 g/mol HO: 18.02 g/mol H22OO

Unknown:Unknown: Formula of hydrate: Formula of hydrate: Name of hydrate: Name of hydrate:

1.1. Determine the mass of water lost.Determine the mass of water lost.

2.2. Calculate the number of moles of HCalculate the number of moles of H22O and anhydrous O and anhydrous CuSOCuSO4 4 using the molar mass.using the molar mass.

3.3. Determine the value of x= moles HDetermine the value of x= moles H22O O ÷ moles ÷ moles CuSOCuSO4 4

4.4. The ratio indicates the number of water molecules The ratio indicates the number of water molecules bonded to CuSObonded to CuSO4 4

5.5. Name the hydrate using the correct prefixName the hydrate using the correct prefix

Practice ProblemPractice Problem A hydrate is found to have the A hydrate is found to have the

following percent composition: 48.8 following percent composition: 48.8 % MgSO% MgSO44 and 51.2% H and 51.2% H22O. What is the O. What is the formula and name for this hydrate? formula and name for this hydrate?