Simplest (Empirical) Formula

• Simplest integer ratio of the atoms in a compound• Assume 100 g of compound, %element is then g

element in sample• g element x 1 mol element = mol element

g element

CHCl3 10.061 g C x 1 mol C = 0.83765 mol C 12.011 g C

Determine simplest integer mole ratio

EXAMPLE: Phosphorus burns in air to produce a white compound that is 43.7% P and 56.3% O by mass. What is the empirical formula of the compound?

mass

43.7g P

56.3g O

Relative Number of Atoms

(mass/atomic mass)

43.7/30.97 = 1.41 56.3/15.9994 = 3.52

Divide by Smaller

1.41/1.41 = 1.003.52/1.41 = 2.50

Multiplyby Integer

2 1.00 22 2.50 5

Empirical Formula P2O5

Assume 100 g of compound

.25, .33, .5, .67, .75 ¼, ⅓, ½, ⅔, ¾1:1.25 = 4:5

Molecular Formula

• The exact proportions of the elements that are contained in a molecule

• An integer multiple (X) of the empirical formula

MF = X EF

Molecular Formula from Simplest Formula

empirical formula mass FM

sum of the atomic weights represented by the empirical formula

molar mass = MM = X FM

Molecular Formula from Simplest Formula

first, knowing MM and FM

X = MM/FM

then

MF = X EF

EXAMPLE: Our phosphorus compound has a molar mass of ~285. What is the molecular formula?

FM = 2 x 30.97 + 5 x 16.00 = 141.94

MM 285X = = = 2 FM 141.94

thus MF = 2 EF

P4O10

The empirical formula of a substance is found to be CH3O and its molecular weight is found

to be roughly 61 g/mol. What is the true molecular weight of the substance?

30.

5 g/m

ol

31.

0 g/m

ol

61.

0 g/m

ol

62.

0 g/m

ol

124

.0 g

/mol

0% 0% 0%0%0%

1. 30.5 g/mol

2. 31.0 g/mol

3. 61.0 g/mol

4. 62.0 g/mol

5. 124.0 g/mol10

0

0

130

Biological Periodic Table

Glucose C6H12O6

Carbohydrates Cx(H2O)y

Sucrose

Glucose + Fructose Sucrose + Water

Tristearin - Glycerol - Stearic Acid

3H2O++3

Chapter 4

Quantities of Reactants

and Products

Balanced Chemical Equation

• Representation of a chemical reaction which uses stoichiometric coefficients (prefix numbers) to represent the relative amounts of reactants and products

• 2 H2 (g) + O2 (g) 2 H2O (l)

• Molecule to Moleculeor Mole to Mole

EXAMPLE How much H2O, in moles results from burning an excess of H2 in 3.3

moles of O2? 2 H2 + O2 2 H2O

(3.3 mol O2) (2 mol H2O)#mol H2O = = 6.6 mol H2O

(1 mol O2)

Mole ratio frombalanced chemical equation

Reaction of H2 and Cl2

H2 (g) + Cl2 (g) 2 HCl (g)

one to one gives two

four to four gives eight

or

Types of Reactions• synthesis or combination reactions

• decomposition reactions

• displacement reactions

• exchange reactions

Types of Chemical Reactions

Synthesis or Combination Reactions

Formation of a compound from simpler compounds or elements.

Combination Reaction

Decomposition Reactions

Separation into constituents by chemical reaction.

Dynamite

Electrolysis

Displacement Reactions

Reaction of a compound with a more reactive element to produce a new compound and release a less reactive element

Displacement Reactions

Exchange Reactions

Reaction where ion partners are exchanged

Pb(NO3)2 (aq) + K2CrO4 (aq) PbCrO4 (s) + 2 KNO3 (aq)

When Zn(s) is placed in aqueous HCl, hydrogen gas is evolved and zinc chloride solution is obtained. Predict the reaction type.

Combi

natio

n

Combu

stio

n

Decom

positio

n

Displa

cem

ent (

singl

e ...

Exchan

ge (d

ouble

di..

.

0% 0% 0%0%0%

1. Combination

2. Combustion

3. Decomposition

4. Displacement (single displacement)

5. Exchange (double displacement)

100

0

130

Writing and BalancingChemical Equations

• Determine the type of reaction and formulae of the products

• Write an unbalanced equation with the correct reactants and products

• Balance the equation by the use of prefixes (coefficients) to balance the number of each type of atom on the reactant and product sides of the equation.

Example

Iron is produced by the reduction of iron(III) oxide with CO which forms CO2

iron(III) oxide + carbon monoxide iron + carbon dioxide

Fe2O3 + CO Fe + CO2

Fe2O3 + CO 2 Fe + CO2

Fe2O3 + 3 CO 2 Fe + 3 CO2

When aluminum reacts with sulfuric acid to yield aluminum sulfate and hydrogen what is the SUM of the

coefficients in the balanced equation?

10

0% 0% 0%0%0%

1. 42. 63. 74. 85. 9

0

0

130