Mole ConceptMole Concept

Counting UnitsCounting Units A A pairpair refers to how many shoes? refers to how many shoes? A A dozendozen refers to how many doughnuts or refers to how many doughnuts or

eggs?eggs? How many pencils are in a How many pencils are in a grossgross?? How many pieces of paper are in a How many pieces of paper are in a reamream??

In chemistry, a counting unit called a In chemistry, a counting unit called a molemole is is used to keep track of the number of atoms, used to keep track of the number of atoms, molecules, or formula units that are in a molecules, or formula units that are in a sample of a substance.sample of a substance.

MoleMole Unit used to measure the amount of a pure Unit used to measure the amount of a pure

substance (abbreviated mol)substance (abbreviated mol) 1 mol = 6.022 x101 mol = 6.022 x102323 representative particles representative particles representative particles are the smallest piece of representative particles are the smallest piece of

any pure substance any pure substance Element – atomsElement – atoms Covalent compounds – moleculesCovalent compounds – molecules Ionic compounds - formulas unitsIonic compounds - formulas units

6.022 x106.022 x102323 is known as Avogadro’s number is known as Avogadro’s number 6.022 x106.022 x102323 can be used as a conversion factor can be used as a conversion factor

to determine the number of particles in a to determine the number of particles in a substancesubstance

Avogadro’s NumberAvogadro’s Number

How big is Avogadro’s Number?How big is Avogadro’s Number?

If you have a mole of pennies (i.e. If you have a mole of pennies (i.e. Avogadro’s number) and divide Avogadro’s number) and divide them equally among the 6 billion them equally among the 6 billion people on Earth, how many people on Earth, how many dollars would each person get?dollars would each person get?

Avogadro’s NumberAvogadro’s Number

6.022 X106.022 X102323 pennies pennies

$1x10$1x101212

6 x 106 x 1099 people people

x x 11 $ =$ = 100 100

Each person would get

~ $ 1 trillion!!!

Molar MassMolar Mass

mass (in grams) of one mole of any mass (in grams) of one mole of any substancesubstance

units are grams per mole (g/mol)units are grams per mole (g/mol) molar mass of any element = the AAM of molar mass of any element = the AAM of

the element from the periodic tablethe element from the periodic table

Examples: Examples:

the molar mass for the molar mass for lithium (Li) = lithium (Li) = manganese (Mn) = manganese (Mn) = silver (Ag) =silver (Ag) =

molar mass of a molecule or molar mass of a molecule or formula unit – number of atoms of formula unit – number of atoms of each element multiplied by the each element multiplied by the mass of each elementmass of each element

Examples: Examples:

HH22OO

Mg(OH)Mg(OH)22

Mole ConversionsMole Conversions

Examples: Examples:

1.1. Determine the mass of 0.0450 mol of chromium.Determine the mass of 0.0450 mol of chromium.

2.2. How many moles are in 3.25 g of water?How many moles are in 3.25 g of water?

3.3. How many particles are there in 2.6 moles of How many particles are there in 2.6 moles of potassium nitrate?potassium nitrate?

4.4. How many molecules of glucose, CHow many molecules of glucose, C66HH1212OO66, are , are

found in a 5.37 g sample?found in a 5.37 g sample?

mole

Percent CompositionPercent Composition is the percent by mass of any element in a is the percent by mass of any element in a

compoundcompound uses molar mass for elements and compoundsuses molar mass for elements and compounds is found by using the following formula:is found by using the following formula:

% of element = % of element = mass of element mass of element x 100 x 100

mass of compoundmass of compound

Example: Example: Determine the percent composition of the Determine the percent composition of the

elements in copper (II) nitrate.elements in copper (II) nitrate.

Empirical FormulasEmpirical Formulas

Empirical formulaEmpirical formula – smallest whole number – smallest whole number mole ratio of elements in a compoundmole ratio of elements in a compound

Solving Empirical Formula ProblemsSolving Empirical Formula Problems

1.1. Grams to molesGrams to moles – use the molar mass to – use the molar mass to convert the grams of each element to molesconvert the grams of each element to moles

2.2. Divide by smallDivide by small – divide the number of moles – divide the number of moles of each element by the smallest number of of each element by the smallest number of molesmoles

example…example…

What is the formula of a What is the formula of a compound that is comprised of compound that is comprised of 56.4g K, 8.7g C and 34.9g 56.4g K, 8.7g C and 34.9g O?O?

Empirical and Molecular FormulasEmpirical and Molecular Formulas

Molecular formulaMolecular formula – the actual number – the actual number of atoms in a molecular compoundof atoms in a molecular compound

Example: glucoseExample: glucose molecular formula: Cmolecular formula: C66HH1212OO66

empirical formula: Cempirical formula: C11HH22OO11

ratio of the elements is the same in both ratio of the elements is the same in both formulas, just reduced in the empirical formulas, just reduced in the empirical formulaformula

To solve molecular formula To solve molecular formula problems…problems…

Calculate the empirical formulaCalculate the empirical formula divide empirical molar mass into the divide empirical molar mass into the

given molecular molar mass, then given molecular molar mass, then distribute whole number answer through distribute whole number answer through empirical formulaempirical formula

example problem…example problem…

Find the molecular formula for a Find the molecular formula for a compound that is known to compound that is known to contain 26.7% phosphorus, contain 26.7% phosphorus, 12.1% nitrogen, and 61.2% 12.1% nitrogen, and 61.2% chlorine. Molecular mass of the chlorine. Molecular mass of the compound is known to be 695 compound is known to be 695 g/mol.g/mol.