simplest (empirical) formula
DESCRIPTION
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 CHCl 3 10.061 g C x 1 mol C = 0.83765 mol C 12.011 g C - PowerPoint PPT PresentationTRANSCRIPT
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