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
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 ca
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 compo
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 t
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 Th
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 dat
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.
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 p
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 gr
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 Zeelan
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
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
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)
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
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 c
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 g
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
Kin
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 1
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
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.
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
bracket
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
- 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