Empirical Formula Example 2
Find the empirical formula of a sample having 37.49 % C, 12.58 % H, 49.93 %
O.
37.49 g C
12.58 g H
49.93 g O
12.011 g/mol
1.0079 g/mol
15.999 g/mol
= 3.121 mol C
12.481 mol H
3.121 mol O
C3.121H12.481O3.121
3.121
3.121
3.121
=
Your Turn Again:
Calculate the percentage composition for aluminum carbonate. (This means
find the percentage by mass of each element in the compound.)
% Composition for aluminum carbonate
aluminum carbonate is Al2(CO3)3
atomic mass / molar mass
x100
%
2
Empirical Formulas
An empirical formula is the mathematically reduced form of a chemical
formula. Several examples.
Empirical Formulas from Percentages
C4.1b Calculate the empirical formula of a compound based on the weight of
each element in a compound.
Molar Mass of Hydrates
The mass of the water is ADDED to the mass of the salt.
Example
MnBr24 H2O
manganese II bromide tetrahydrate
Mn
2 Br
54.9
2 x 79.9
4 H2O + 4 x
18.0
286.7 g/mol
Remember to ADD the mass of water.
Nomenclature and Formula Mass
Formula
The Percentage Composition Calculation allows us to calculate the
percentage of mass for each element in a compound.
Sodium hydroxide is NaOH.
Na 23.0 g/mol
16.0 g/mol
H
+ 1.0 g/mol
40.0 g/mol
Find The Percentage of Each Element
% Na = 23 x 100 = 57.5 % N
Most Common Isotope
C4.10d Predict which isotope will have the greatest abundance given the
possible isotopes for an element and the average atomic mass in the periodic
table.
For the most precise data, this is an item one would normally look up.
Butif no
30 grams hydrogen sulfate (answer)
Hydrogen sulfate is H2SO4
The molar mass is 98.1 g/mol
30 grams x 1mol
= 0.31 mol H2SO4
98.1 grams
30 grams x 1mol
x 6.022 x 1023 formula units
98.1 grams
1 mol
= 1.84 x 1023 formula units hydrogen sulfate
Your Turn
You
Warm-Downsnot in packet
What is the mass of 6.78x1024 formula units of barium hydroxide?
Plan
Formula units moles grams
6.78x1024 f.u.
1 mol
171.3 g Ba(OH)2
6.022x1023 f.u.
1
1 mol
Warm Downs-not in packet
How many molecules in 1 teaspoon of water?
1 tsp
Simple Sample #2
If 33.3 % of our class weighs 100 lbs, 33.3 % weighs 120 lbs and 33.3 %
weighs 140 lbs what is the average weight?
Simple Sample #3
If 20 % of the textbooks in our school weigh 500 grams each and 80 % weigh
600 grams each, what is the ave
Simple Solution #4
Drenthonium
0.20 x 75 g/mol
Borculonium
0.30 x 100 g/mol
Beaverdamium
+
0.50 x 106 g/mol
Zeelandium
98 g/mol
This is called the weighted average mass of the three isotopes of Zeelandium.
The atomic masses on the periodic table are weigh
Molar mass allows us to convert from molar heat capacity to specific heat
capacity.:
Water has a molar heat capacity of 75.3 J/(molC). Find its specific heat
capacity in cal/(g C).
75.3 J
mol C
1 mol H2O
18 g
1 cal
=
4.184 J
0.9998 cal
gC
Suppose you eat
Which will have the greatest reaction rate and why?
Catalyst
A Catalyst generally speeds up a reaction.
The Catalytic converter in your car speeds up the decomposition of Harmful
NO,NO2, N2O4 into N2 and O2. In general a catalyst holds a molecule in the
c
Hess Law Example 2 (optional)
Calculate the enthalpy of formation of carbon dioxide from its elements:
C(g) + 2O CO2 (g)
Use the following equations:
2O O2
H = -250 kJ
C(s) C(g)
H = +720 kJ
CO2 (g) C(s) + O2
H = +390 kJ
Answer-Give it some think time
W
Activation Energy
The Activation Energy represents an Energy Barrier to formation of the
products. Some form of energy must be present to supply this energy in order
for a reaction to occur. It can be a small or a large amount, depending on the
size of th
Hess' law
Germain Henri Hess (1802 - 1850) is important primarily for his
thermochemical studies, which began in 1839; his other work was of less
importance. The key paper was published in 1840. The contributions of Hess
to heat can be summed up in what i
For Exothermic reactions:
A + 2B D + 250 J
Or
A + 2B D
H = -250J
For Endothermic Reactions
D + 250 J A + 2B
Or
D
A + 2B
H = 250J
Heat in a Reaction
C3.1d Calculate the amount of heat produced for a given mass of reactant
from a balanced reaction.
Recall
Thermodynamics
AshortUnit
Chapter10Holt
Terminology
Thermodynamics
is the study of heat transfer from 1 object to another.
Heat Transfer happens during phase changes and chemical reactions.
Review
Kinetic Energy
This is energy due to motion
Individual mol
Heat Units
BTU
British Thermal Units
(A non-metric unit of heat
used in USA)
calories heat needed to raise
1 gram of water by 1
degree C
Calories 1 Food Calorie = 1000 calories, 1 Calorie will raise 1000 g of water
by 1 C
Joules
Metric unit of heat.
4.184
GoodLordItsMoreTerminology
C3.1d Calculate dH for a chemical reaction using a simple coffee calorimeter.
Specific Heat Capacity Cp describes how much heat is needed to change
the temperature of 1 gram something
Water is 4.184 J/(gC) or 1.000 cal /(g C)
Mo
13-2 Practice
Calculating pH
1. Determine the pH of a 0.033 M solution of HNOa, a strong acid. (Hint: see Sample Prob-
lem 13B.)
Use the problem-
solving strategies
below to solve items
110.
List what you know
0 List all
1.,
is.
Name Class Date
Skills Worksheet
Concept Review
Section: Solubility and the DissolVing Process
Complete each statement below by underlining the correct word or phrase in
brackets.
1. TWO liquids that are soluble in each other in al
W"
I Solutions Manual continued
46. Given: 12.5 kg shark meat (22 mg CH3Hg+)(i> = 0.022 g CHaI-Igr
22 mg CHaHg+ 1000 mg
legal limit = 1000 g
1.00 ppm 1 kg
Unknown: is this within 0.022 g CHgHg+ _ x
the legal limit 12500 g meat ' 1 000 000 g
___ (0.022
- Boyles Law
Boyles Law sTaTes ThaT The volume of a gas varies inversely wiTh
iTs pressure if TemperaTure is held consTanT. (if one goes up, The .
oTher goes down.) We use The formula: -
Ple1=P2xV2
Solve The following problems (assuming consTanT Temper