simplest (empirical) formula simplest integer ratio of the atoms in a compound assume 100 g of...
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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
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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
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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
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Molecular Formula from Simplest Formula
empirical formula mass FM
sum of the atomic weights represented by the empirical formula
molar mass = MM = X FM
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Molecular Formula from Simplest Formula
first, knowing MM and FM
X = MM/FM
then
MF = X EF
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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
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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
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Biological Periodic Table
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Glucose C6H12O6
Carbohydrates Cx(H2O)y
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Sucrose
Glucose + Fructose Sucrose + Water
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Tristearin - Glycerol - Stearic Acid
3H2O++3
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Chapter 4
Quantities of Reactants
and Products
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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
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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
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Reaction of H2 and Cl2
H2 (g) + Cl2 (g) 2 HCl (g)
one to one gives two
four to four gives eight
or
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Types of Reactions• synthesis or combination reactions
• decomposition reactions
• displacement reactions
• exchange reactions
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Types of Chemical Reactions
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Synthesis or Combination Reactions
Formation of a compound from simpler compounds or elements.
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Combination Reaction
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Decomposition Reactions
Separation into constituents by chemical reaction.
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Dynamite
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Electrolysis
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Displacement Reactions
Reaction of a compound with a more reactive element to produce a new compound and release a less reactive element
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Displacement Reactions
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Exchange Reactions
Reaction where ion partners are exchanged
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Pb(NO3)2 (aq) + K2CrO4 (aq) PbCrO4 (s) + 2 KNO3 (aq)
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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
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ent (
singl
e ...
Exchan
ge (d
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.
0% 0% 0%0%0%
1. Combination
2. Combustion
3. Decomposition
4. Displacement (single displacement)
5. Exchange (double displacement)
100
0
130
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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.
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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
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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