CH 11: The Mole

Section 1 Counting Matter

Counting Matter

What are some everyday ways we count matter?

1.

2.

3.What about molecules? Or atoms?

DOZEN = 12 things

BUSHEL of corn = 21.772 kg

1 GROSS = 144 things

1 MOLE = ???

The Mole It represents a

counted number of things.

IN Chemistry the term MOLE represents the number of particles in a substance.

In Chemistry is NOT this furry little animal or the spot on your face…

Just how many is a mole? One mole represents 6.02 x 1023 of things

(units, molecules, compounds, formula units). This is called Avogadro’s number.

One mole of most elements contains 6.02 x 1023 atoms.

1 mole O2 = 6.02x1023 molecules of O2

602 000 000 000 000 000 000 000

Just how big is a mole? Listen to The Mole Song! An Avogadro's number of standard soft drink

cans would cover the surface of the earth to a depth of over 200 miles

If you had Avogadro's number of un-popped 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.

Solving the Problems Samples Required: dimensional analysis/factor label

How many molecules are in 3.00 moles of N2?

How many moles of Na are in 1.10 x 1023 atoms?

molecules 1081.1N mole 1

N molecules 10 x 6.02N moles 3 24

2

223

2

Na moles 182.0Na atoms 10 x 6.02

Na mole 1atoms 1010.1

2323

Practice moles to particles

Determine the number of atoms in 2.50 mol Zn.

Given 3.25 mol AgNO3, determine the number of formula units.

Calculate the number of molecules in 11.5 mol H2O.

Practice Particles to Moles

How many moles contain each of the following?5.75 x 1024 atoms Al3.75 x 1024 molecules CO2

3.58 x 1023 formula units ZnCl22.50 x 1020 atoms Fe

11-2 Mass & the Mole 11-3 Moles of Compounds

Molar Mass Defn: is the mass (think grams) of one

mole of a substance Atomic masses (from periodic table)

represent molar mass. Units g/mol 1 mole of Carbon has 6.02 x 1023 atoms of C

and they have a mass of 12.01 grams. To calculate the molar mass of a

compound, you add up the molar masses of all the elements in that compound

Molar Mass Practice

What is the mass of 1.00 mole of Oxygen? Of Nitrogen?

Find the molar mass for: SO3

Na2SO4

Molar Mass Calculator for homework helpTutorial Site

1 mole O = 16.0 grams

1 mole N = 14.0 grams

SO3= 80 g/mole

1 Mole = 142.043g

Molar Mass Practice

When you see 1.00 mole = _?_ g, think “g means GO to the PERIODIC TABLE” to find the molar mass.

http://www.webelements.com/

Practice Problems

Determine the molar mass of each of the following ionic compounds: NaOHCaCl2KC2H3O2

HCNCCl4H2O

Grams-Mole Conversions

How many moles are in 56.8 g of HCl?

How many grams are in .05 moles Na2SO4?

HCl moles 58.1HCl g 36

HCl mole 1 HCl g 8.56

4242

4242 SONa g 5.4

SONa mole 1

SONa g 90SONa mole 05.

Practice Mole to Grams

Determine the mass in grams of each of the following.3.57 mol Al42.6 mol Si3.45 mol Co2.45 mol Zn

Practice Gram to Mole

How many atoms are in each of the following samples?55.2 g Li0.230 g Pb11.5 g Hg45.6 g Si0.120 kg Ti

Ex: Mass to Particle Conversion Gold is one of a group of metals called the coinage

metals (copper, silver and gold). How many atoms of gold (Au) are in a pure gold nugget having a mass of 25.0 g?

Known: Unknown:

Mass = 25.0 g Au

Molar mass Au = 196.97 g/mol Au

25.0 g Au x 1 mole Au x 6.02 x 1023 atoms Au = 7.65 x 1022 atoms Au

196.97 g Au 1 mol Au

Number of atoms = ? Atoms Au

Practice Problems

How many atoms are in each of the following samples?55.2 g Li0.230 g Pb11.5 g Hg45.6 g Si0.120 kg Ti

Ex: Particle to Mass Conversion A party balloon contains 5.50 x 1022 atoms of helium

(He) gas. What is the mass in grams of the helium?

Known: Unknown:

Number of atoms = 5.50 x 1022 atoms He

Molar mass He = 4.00 g/mol He

5.50 x 1022 atoms He x 1 mol He x 4.00 g He = 0.366 g He

6.02 x 1023 atoms He 1 mol He

Mass = ? G He

Practice Problems

What is the mass in grams of each of the following?6.02 x 1024 atoms Bi1.00 x 1024 atoms Mn3.40 x 1022 atoms He1.50 x 1015 atoms N1.50 x 1015 atoms U

Molar Volume

The volume of a gas is usually measured at standard temperature and pressure (_STP_)

Standard temp = ___0°_ C Standard pressure = ___1___ atmosphere

(atm) 1 mole of any gas occupies __22.4__ L of

space at STP

Molar Volume Practice

How many moles would 45.0 L of He gas be?

How many liters of O2 would 3.8 moles occupy?

Putting it all together

1.0 mole = _6.02 x 1023___atoms or molecules 1.0 mole = _?__ g(PT)

1.0 mole = _22.4 L (at STP)

Helpful Chart!

Volume in Liters

Grams

MOLES

Atoms or Molecules

Chemical Formulas and the Mole

Chemical formula for a compound indicates the types of atoms and the number of each contained in one unit.Ex. CCl2F2 - Freon

Ratio of carbon to chlorine to fluorine is 1:2:2 Ratios can be written: or

In one mole of freon you would have 1 mole of carbon, 2 moles of chlorine and 2 moles of fluorine.

Ex: Mole Relationship from Chemical Formulas

Determine the moles of aluminum ions (Al3+) in 1.25 moles of aluminum oxide

1.25 molAl2O3 x 2 mol Al3+ ions = 2.50 mol Al3+ ions

1 mole Al2O3

Practice Problems Determine the number of moles of chloride ions

in 2.53 mol ZnCl2. Calculate the number of moles of each element

in 1.25 mol glucose (C6H12O6). Determine the number of moles of sulfate ions

present in 3.00 mol iron (III) sulfate (Fe(SO4)3). How many moles of oxygen atoms are present

in 5.00 mol diphosphorus pentoxide? Calculate the number of moles of hydrogen

atoms in 11.5 mol water.

11-4 Empirical & Molecular Formulas

Percent Composition

the percentage by mass of each element in a compound

The percent comp. is found by using the following formula:

100compound of massmolar

element 1 of mass Mass %

Percent Composition Example

Ex. Compound XY is 55g element X and 45g element Y

55 g of element X x 100 = 55 % element X

100 g of compound

45 g of element Y x 100 = 45 % element Y

100 g of compound

Percent Composition from Chemical Formula

First find the molar mass of each element and the molar mass of the compound

Ex: what is the % composition of H in 1 mole of H2O? Multiply the molar mass of the element by its

subscript in the formula. 1.01 g/mol H x 2 mol = 2.02 g H

% by mass H = 2.02 g x 100 = 11.2% H

18.02 g H2O

Percent Composition from Chemical FormulaExample continued – Molar mass of O for each mole of H2O? 16.00 g/mol O x 1mol O = 16.00 g O

16.00 g x 100 = 88.8 % O

18.02 g

% Composition Practice

What is the percent of C & H in C2H6?

What is the percent of each element in Na2SO3?

Empirical Formulas This is the LOWEST whole number ratio of

the elements in a compound. For example, the empirical formula for

Molecular Formula C6H6 Empirical Formula CH

What is the empirical formula for each? C2H6

C6H12O6

11-3: Calculating Empirical Formula

Steps for caluculating Empirical Formula give mass or percent composition:

1. If given a percent sign (%), remove the sign & change to GRAMS.

You are assuming you have 100 g of the compound.2. Convert grams ---> moles.3. Select lowest number of moles4. Divide each number of moles by this number.5. If the number divides out evenly, these are the

subscripts of the elements in the compound.6. If any of the numbers have a .5, MULTIPLY them

ALL by TWO & then place these numbers as the subscripts.

Example Using Percent Composition The percent composition of an oxide of

sulfur is 40.05% S and 59.95% O. Assuming you have a 100g sample, it contains 40.05g S and 59.95g O.

Convert to moles using molar mass:40.05g S x 1 mol = 1.249 mol S

32.07g59.95g O x 1 mol = 3.747 mol O

16.00g

Example Using Percent CompositionThe mole ratio of S atoms to O atoms in the oxide

is 1.249 : 3.747.Recognize that S has the smallest possible

number of moles at ~1. Make the mole value of S equal to 1 by dividing both mole values by 1.249.

1.249 mol S = 1 mol S 1.249

3.747 mol O = 3 mol O1.249

The simplest whole number mole ratio of S atoms to O atoms is 1 : 3. The empirical formula for the oxide of sulfur is SO3.

Sample Problems

What is the empirical formula for a compound which is 75 % C and 25 % H?

What is the empirical formula for a compound which has 48.64 % C, 8.16 % H 43.20 % O

Sample Problems #2

What is the empirical formula of 40.68 % C5.08 % H54.24 % O

Practice Problems

A blue solid is found to contain 36.894% N and 63.16% O. What is the empirical formula for this solid?

Determine the empirical formula for a compound that contains 35.98% Al and 64.02% S.

Propane is a hydrocarbon, a compound composed only of carbon and hydrogen. It is 81.82% C and 18.18% H. What is the empirical formula?

The chemical analysis of aspirin indicates that the molecule is 60.00% C, 4.44% H and 35.56% O. Determine the empirical formula.

What is the empirical formula for a compound that contains 10.89% Mg, 31.77% Cl, and 57.34% O?

Molecular Formula

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

n= ratio between experimentally determined mass of compound and the molar mass of the empirical formula.

Calculating Molecular Formula Molar mass of acetylene – 26.04 g/mol

Mass of empirical formula (CH) – 13.02 g/mol n – Obtained by dividing the molar mass by the mass of the

empirical formula indicates that the molar mass of acetylene is two times the mass of the empirical formula.

Experimentally determined molar mass of acetylene = 26.04 g/mol = 2.000 mass of empirical formula CH 13.02 g/mol

Molecular Formula = (CH)2

Acetylene = C2H2

Determining a Molecular Formula Succinic acid is a substance produced by lichens.

Chemical analysis indicates it is composed of 40.68% C, 5.08% H, and 54.24% O and has a molar mass of 118.1 g/mol. Determine the empirical and molecular formulas for succinic acid.

Known: Unknown:

Percent by mass = 40.68% C empirical formula = ?

Percent by mass = 5.08% H molecular formula = ?

Percent by mass = 54.24% O

Practice Problems

Analysis of a chemical used in photographic developing fluid indicates a chemical composition of 65.45% C, 5.45% H, and 29.09% O. The molar mass is found to be 110.0 g/mol. Determine the molecular formula.

A compound was found to contain 49.98 g C, and 10.47 g H. The molar mass of the compound is 58.12 g/mol. Determine the molecular formula.

A colorless liquid composed of 46.68% N and 53.32% O has a molar mass of 60.01 g/mol. What is the molecular formula?

11-4 The Formula for a Hydrate

Naming Hydrates

Hydrate: a compound that has a specific number of water molecules bound to its atoms.

In the formula for a hydrate, the number of water molecules associated with each formula unit of the compound is written following a dot.

ex. Na2CO3·10H2Ocalled sodium carbonate decahydratedeca- means 10 and hydrate means water

Therefore there are 10 water molecules are associated with one formula unit of the compound.

Formulas for Hydrates and Examples

Prefix Molecules H2O Formula Name

Mono- 1 (NH4)2C2O4·H2O Ammonium oxalate monohydrate

Di- 2 CaCl2·2H2O Calcium chloride dihydrate

Tri- 3 NaC2H3O2·3H2O Sodium acetate trihydrate

Tetra- 4 FePO4·4H2O Iron(III) phosphate tetrahydrate

Penta- 5 CuSO4·5H2O Copper(II) sulfate pentahydrate

Hexa- 6 CoCl2·6H2O Cobalt(II) chloride hexahydrate

Hepta- 7 MgSO4·7H2O Magnesium sulfate heptahydrate

Octa- 8 Ba(OH)2·8H2O Barium hydroxide octahydrate

Deca- 10 Na2CO3·10H2O Sodium carbonate decahydrate

Analyzing a Hydrate

Must drive off the water by heating the compound

Substance remaining after heating is anhydrous (without water)

Example: hydrated cobalt(II) chloride is a pink solid that turns a deep blue when the water of hydration is driven off and anhydrous cobalt(II) chloride is produced

Formula for a Hydrate

To determine the formula for a hydrate, you must determine the number of moles of water associated with one mole of the hydrate.

Example Problem – Determining the Formula for a Hydrate

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 white anhydrous copper sulfate (CuSO4) remains. What is the formula for the hydrate? Name the hydrate.

Example Problem – (cont.)

Known:

Mass of hydrated compound = 2.50 g CuSO4·xH2O

Mass of anhydrous compound = 1.59 g CuSO4

Molar mass = 18.02 g/mol H2O

Molar mass = 159.6 g/mol CuSO4

Unknown:

Formula for hydrate = ?

Name of hydrate = ?

Example Problem – (cont.)

Subtract the mass of the anhydrous copper sulfate from the mass of the hydrated copper sulfate to determine the mass of water lost:mass of hydrates copper sulfate 2.50 gmass of anhydrous copper sulfate - 1.59 gmass of water lost 0.91 g

Calculate the number of moles of H2O and anhydrous CuSO4

1.59 g CuSO4 x 1 mol CuSO4 = 0.00996 mol CuSO4

159.6 g CuSO4

0.91 g H2O x 1 mol H2O = 0.050 mol H2O

18.02 g H2O

Example Problem – (cont.)

Determine the value of x.

x = moles H2O = 0.050 mol H2O = 5.0 mol H2O = 5

moles CuSO4 0.00996 mol CuSO4 1.0 mol CuSO4 1

The ratio of H2O to CuSO4 is 5 : 1, so the formula for the hydrate is CuSO4·5H2O, copper(II) sulfate pentahydrate.

Practice Problems

A hydrate is found to have the following percent composition: 48.18% MgSO4 and 51.2% H2O. What is the formula and name for this hydrate?

If 11.75 g of the common hydrate cobalt(II) chloride is heated, 9.25 g of anhydrous cobalt chloride remains. What is the formula and name for this hydrate?

Uses of Hydrates

Drying agents: CaCl2, CaSO4

Storage of solar energy: Na2SO4·10H2O