+
The Mole
Chapter 10
+
Previous Skills required for this
chapter

Writing formulas from names for:

Ionic compounds

Covalent compounds

Acids

Balancing equations

Predicting Products

Minor emphasis, but still needed
+
Skills to be learned

Determining molar mass

Elements

Compounds

Determining number of moles within a compound

Molar conversions

Mole to mole; gram to mole; mole to gram; gram to mole; mole to
atoms; atoms to mole

Empirical Formula and Molecular formula

Formulas and naming hydrates
+
The mole, what is it?
+
Mole

6.02x1023 atoms

For a given molecule, one mole is a mass (in grams)
whose number is equal to the atomic mass of the
molecule.

In general, one mole of any substance contains
Avogadro's Number of molecules or atoms of that
substance.

This relationship was first discovered by Amadeo
Avogadro (1776-1858) and he received credit for this after
his death.
+
Molar mass

Unit: g/mol

The amount of mass (in grams) for every one mole of the
element or molecule.

For elements:
+
Molar Mass

For compounds
+
Conversion factors of molar mass
+
Empirical and molecular formulas

Percent composition from experimental data
massofelement
%bymass(element) =
´100
massofcompound
+
Empirical and molecular formulas

Percent composition from the chemical formula
massofelementin1molofcompound
%bymass =
´100
molarmassofcompound
+
Problems

What is the percent composition of phosphoric acid?

Which has the larger percent by mass of sulfur: H2SO3 or
H2S2O8?

Calcium chloride is sometimes used as a de-icer. Calculate
the percent by mass of each element in CaCl2.

Challenge: Sodium sulfate is used in the manufacture of
detergents.



Identify each of the component elements of sodium sulfate, and
write the compound’s chemical formula.
Identify the compound as ionic or covalent.
Calculate the percent by mass of each element in sodium sulfate.
+
Empirical Formula
is the formula with the smallest wholenumber mole ratio of the elements.

Steps to finding empirical formula.

Given Percent by mass.

Convert to moles.

Determine the smallest value.

Divide all numbers by smallest value.

If whole numbers, they are the subscripts. If they are not, multiply
in order to reach a whole number.
+
Step One: Given Percent by mass

If given percentage, turn % into g.

If given grams, continue on.
+
Step Two: Convert to moles.
+
Step Three: Determine the smallest
value.
+
Step Four: Divide by smallest
number.
+
Step Five: Answer?
+
Problems

Determine the empirical formula for a compound that
contains 35.98% aluminum and 64.02% sulfur.

Propane is a hydrocarbon, a compound composed only of
carbon and hydrogen. It is 81.82% carbon and 18.18%
hydrogen. What is the empirical formula?

Aspirin is the world’s most-often used medication. The
chemical analysis of aspirin indicates that the molecule is
60.00% carbon, 4.44% hydrogen, and 35.56% oxygen.
Determine the empirical formula for aspirin.
+
Molecular Formula
specifies the actual number of atoms of
each element in one molecule or formula unit of the substance.

Steps to determine Molecular formula








Given Percent by mass.
Convert to moles.
Determine the smallest value.
Divide all numbers by smallest value.
If whole numbers, they are the subscripts. If they are not, multiply in
order to reach a whole number.
Determine the molar mass of the EF (answer from previous step)
Divide molar mass of EF by molar mass of MF (given)
Multiply EF by answer in previous step.
+
Step One: Given Percent by mass

If given percentage, turn % into g.

If given grams, continue on.
+
Step Two: Convert to moles.
+
Step Three: Determine the smallest
value.
+
Step Four: Divide by smallest
number.
+
Step Five: Answer?
+
Step Five: Empirical Formula
+
Last o’ the steps:
+
Problems

A compound was found to contain 49.98g of carbon and
10.47g of hydrogen. The molar mass of the compound is
58.12g/mol. Determine the molecular formula.

A colorless liquid composed of 46.68% nitrogen and 53.32%
oxygen has a molar mass of 60.01g/mol. What is the
molecular formula?

When an oxide of potassium is decomposed, 19.55g of K and
4.00g of O are obtained. What is the empirical formula?
+
Formulas of Hydrates
is a compound that has a specific number of water
molecules bound to its atoms.

Naming Hydrates on next slide

Anhydrous – without water
+ Prefix
Molecules
of 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(III) chloride
hexahydride
Hepta-
7
MgSO47H2O
Magnesium sulfate
heptahydrate
Octa
8
Ba(OH)28H2O
Barium hydroxide
octahydrate
Deca
10
Na2CO310H2O
Sodium carbonate
pentahydrate
+
Steps for determining hydrate
formulas
1.
Determine given
2.
Determine mass of water lost
3.
Convert masses to moles
4.
Solve for ratio of moles of water to moles of solid
5.
Write formula
+
Step One
A
20g sample of a hydrate of nickel
sulfate (NiSO4) lost 9.63g of water
when heated. Determine the
hydrate’s formula.

Hydrate is 20g

Water lost 9.63g
+
Steps continued. . .
+
Problems

An 11.75g 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?
+
Uses of hydrates

Hydrates absorb water


Desiccants prevent moisture from intergering with the sensitive
electronic circuitry
Some store solar energy

When the Sun’s energy heats the hydrate to a temperature greater
than 32 degrees Celsius, the single formula unit of Na2SO4 in the
hydrate dissolves in the 10mol of water of hydration. In the
process, energy is absorbed by the hydrate. This energy is
released when the temperature decreases and the hydrate
crystallizes again.
+
The End