Transcript THE MOLE - bYTEBoss

“THE MOLE”
Counting Quantities
1.) You can count how many of something you
have……
12 doughnuts in a dozen
10 pins knocked down for a strike
2.)
You can measure the mass of what you
have…….
buying candy by the pound
gold is priced by the gram
3.)
You can measure matter by volume…..
gasoline by the liter
medicine in mL
“THE MOLE”
(Molar Mass = 1 MOLE)
A convenient standard quantity of
a substance
For solids, liquids, gases…..you
can convert weight to moles, or
moles to weight
The amount of a substance = in
grams to the sum of the atomic
weights
1 mole =6.02 x 1023 particles
• What do I mean when I say particles?
–Can be atoms, molecules, formula units,
or ions.
ELEMENT
use atoms
COVALENT COMPOUND use molecules
IONIC COMPOUND
use formula units
ION
use ions
Examples
• Na
– I mole of Na = 6.02 x 1023 atoms of Na
• H 2O
– 1 mole of H2O = 6.02 x 1023 molecules of H2O
• NaCl
– 1 mole of NaCl = 6.02 x 1023 formula units of NaCl
• Cl– 1 mole of Cl- = 6.02 x 1023 ions of Cl-
MOLAR MASS AND NUMBER OF
PARTICLES
Substance
Carbon (C)
Sodium (Na)
Molar Mass Number of Particles
in One Mole
12.0 g
6.02 x 1023 C atoms
23.0 g
6.02 x 1023 Na atoms
CaCO3 (antacid)
formula
100.1 g
6.02 x 1023 CaCO3
units
C6H12O6 (glucose)
180.0 g
6.02 x 1023 glucose
molecules
C8H10N4O2 (caffeine) 194.0 g
6.02 x 1023
caffeine molecules
Example problems
• How many moles is 3.46 x
molecules of water?
26
10
• How many moles of hydrogen are
in 3.46 x 1026 molecules of water?
• How many atoms is 3.46 moles of
silver?
A dozen…
• Will a dozen trucks have the
same mass as a dozen
chocolates?
• Will 6.02 x
molecules
of water have the same
23
mass as 6.02 x 10
molecules of CO2?
23
10
Atomic Mass Unit (AMU)
• AMU = mass of a single
atom
• AMU are relative values
based on the mass of the
most common isotope of
carbon.
Molar Mass
• More convenient to use
UNITS:
g/mol
• MM= mass of one mole of
a substance
….remember???
Molar Mass
Use periodic table to find MM of a
compound:
1.
Multiply each element’s
mass (from the periodic
table) by number of atoms
present
2.
Add all the masses together
Practice Problem
• Find the molar mass of
(NH4)2O
Did you get 52 g/mol?
• How many grams is 2.35
moles of MgO?
Practice Problem
• How does the amount of
moles of 44 g of CO2
compare to 36.6 g of HCl?
–Same amount of moles;
therefore, same amount of
23
molecules (6.02 x 10 )
Example
• How many moles is 300 g CO2?
• 1. Determine the relationship between g
CO2 and moles of CO2 (find molar mass)
• 2. Cancel out units and solve.
Solution
44 g CO2 = 1 mole CO2
300 g CO2
1 mole CO2
44 g CO2
= 6.82 mole CO2
Example
• How many molecules is 6.82 moles CO2?
• Determine the relationship between
moles of CO2 and molecules CO2
(Avogadro’s number)
• 2. Cancel out units and solve.
Solution
23 molecules
6.02
x
10
6.82 mole CO2
1 mole CO2
= 4.11 x 1024
molecules CO2
• NOTICE: to get from grams to
molecules you have to go through
the MOLE
– Remember in chemistry all roads lead
to the mole!
MOLAR VOLUME
• PV=nRT
– What is the volume of 1 mole of gas
of oxygen at STP?
– What is the volume of 1 mole of gas
of hydrogen at STP?
MOLAR VOLUME
• Gases can change volume based on
temperature and pressure
• BUT at STP 6.02 x 1023 molecules (1
mole) = 22.4 L
– This is true of ANY gas!
– How many liters are in 12.3 moles of H2SO4
(gas) at STP?
12.3 moles H2SO4 22.4 Liters
1 mole H2SO4
= 276 liters H2SO4
Mole Road Map
Example
• What volume is occupied by 90 g CO2
at STP?
• 1. Determine conversion factors
• 2. Use factor label
1 mole CO2 = 44 g CO2
1 mole CO2 (at STP) = 22.4 L CO2
90 g CO2
1 mole CO2 22. 4 L CO2
44 g CO2
1 mole CO2
= 45.8 L CO2
HAPPY VALENTINE’S DAY
• Make a poem!!!
ROSES ARE RED
VIOLETS ARE BLUE
MOLAR MASS SURE IS SWEET
AND MOLAR VOLUME IS TOO
MOLE MOVIE
• http://www.learner.org/resources/series61.ht
ml#
BELLWORK
2-16
• Convert 3.49 x 1029 ions of PbCl2 to
moles.
• What is the mass of hydrogen in 50.0
grams of C3H8?
PERCENT COMPOSITION
• Relative amounts of elements in a
compound are expressed as PERCENT
COMPOSITION.
% composition steps
• Step 1: Find the total mass of the
compound
• Step 2: Divide the total mass of each
element by the total mass of the
compound
• Step 3: Multiply by 100
Example
• K2CrO4
• Total mass = 2 K (39.1 x 2)
+ Cr (52)
+ 4 O (16 x 4)
194.2 g
• K: 78.2 g/ 194.2 g =
.403 x 100 = 40.3% K
• Cr: 52 g/ 194.2 g =
.268 x 100 = 26.8 % Cr
• O: 64 g/ 194.2 g =
.329 x 100 = 32.9 % O
32.9 % + 26.8 % + 40.3% = 100%
CAFFEINE: C8H10N4O2
ELEMENT
Carbon 12(8)= 96
grams
96/194= .4948 x100
Hydrogen 1(10)= 10
grams 10/194= .052
x100
Nitrogen 14(4)= 56
grams 56/194= .289
x100
Oxygen
16(2)= 32
grams 32/194= .165
x100
PERCENT
COMPOSITION
49.5%
5.2%
28.9%
16.5%
EMPIRICAL FORMULAS
• The lowest whole-number ratio of the
atoms of the elements in a compound
• Is C2O4 an empirical formula?
•
CO2
1:2 ratio between Carbon and Oxygen
• Is H2SO4 an empirical formula?
– Yes, because you can’t reduce the subscripts
any further. (2:1: 4 ratio)
• A compound is analyzed and found to
contain 25.9% nitrogen and 74.1%
oxygen. What is the empirical formula of
the compound?
STEPS FOR EMPIRICAL
FORMULA PROBLEMS
• sTeP 1: change all percents of elements to
grams
• sTeP 2: divide grams of each element by
molar mass of each element- this will give
you moles of each element
• sTep 3: divide moles of each element by
the smallest amount of moles
• sTeP 4: if the ratios are not in whole
numbers multiply each by the smallest
whole number that will convert both
subscripts to whole numbers
Example Problem
• Step 1: 25.9 grams of Nitrogen
74.1 grams of Oxygen
• Step 2: 25.9 g x 1 mol = 1.85 mol N
14 g
74.1 g x 1mol = 4.63 mol O
16 g
• Step 3: 1.85 mol N/ 1.85 = 1 mol N
4.63 mol O/ 1.85 = 2.5 mol O
• Step 4: multiply mol N and mol O by 2 to get whole
numbers: 2 mol N and 5 mol O
• Empirical formula equals N2O5
Class work
• What is the empirical formula of a
compound that is 52.5% Phosphorus and
47.5% Oxygen?
• What is the empirical formula of a
compound that is 10.0% C, .80% H, and
89.1% Cl?
• What is the empirical formula of a
compound that is 7.8% C and 92.2% Cl?
Did you get these answers?
• P4O7
• CHCl3
• CCl4
Bellwork 2/20
• #1: Which of the following can be
classified as an empirical formula?
a) SCl2 b) C6H10O4
c) Na2SO3
• #2: What is the empirical formula of a
compound that is 60.0 % Magnesium and
40.0% oxygen?
SOLUTION
• #1: a and c are empirical formulas
• #2: Change % to grams
• 60.0% Magnesium= 60.0 g Magnesium
• 40.0 % Oxygen = 40.0 g Oxygen
• 2. Convert the grams of each element to
moles (using the molar mass)
60.0 g Magnesium
1 mole Magnesium
24.3 g Magnesium
= 2.46 moles Magnesium
Solution Continued
• Oxygen:
40.0 g Oxygen
1 mole Oxygen
16.0 g Oxygen
= 2.50 moles Oxygen
Solution Continued
• 3. Now divide the number of moles for
each element by the smallest number of
moles.
• 2.46 moles Magnesium
• 2.50 moles Oxygen
• Magnesium has the smallest number of
moles {2.46 moles}
• So divide the number of moles of
Magnesium and Oxygen by 2.46
Solution Continued
• Magnesium = 2.46 moles / 2.46 moles
= 1 Mg
• Oxygen = 2.50 moles / 2.46 moles
= 1.02 O
• Mg1O1
•MgO is the empirical formula
MOLECULAR FORMULAS
• Is a simple whole-number multiple of the
empirical formula
– Can be the same as its experimentally
determined empirical formula.
– EXAMPLE: C8H16 is the molecular formula
CH2 would be the empirical
formula
STEPS FOR FINDING
MOLECULAR FORMULA
• Step 1: First find the empirical formula
following the steps given previously
(sometimes it may be given to you)
• Step 2: Divide molar mass of compound
by empirical formula mass.
• Step 3: Multiply each subscript in the
empirical formula by the value you got in
step 2.
• The molar mass of a a compound is 90
g/mol. The empirical formula is CH2O.
What is the molecular formula?
• Solution: 90/30= 3
– Therefore, molecular formula = C3H6O3
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Slide 12 of 26
• What is the molecular formula of the
compound if the empirical formula is CO2
and the molecular mass is 132 g?
• Nicotine, a component of tobacco, has an
empirical formula of C5H7N. The molar
mass of nicotine is 162 g. What is its
molecular formula?
• A compound contain 64.9% C, 13.5% H,
and 21.6% O. Its molecular mass is 74 g.
Find the molecular formula.
• What is the molecular formula of a
compound with an empirical formula of
CH4N and molecular mass of 60?
• The molar mass of CH4N is 30 g.
• The molecular mass is 60 g.
• Thus, molecular mass of CH4N / empirical
gfm
• 60 g / 30 g
• =2
• You need to multiply each atom in the
empirical by a factor “2”
• Thus CH4N becomes C2H8N2
• C2H8N2 is the molecular formula
HYDRATES
• Hydrates are compounds that contain
weakly bound water molecules as part of
its crystal structure.
– Appear dry
• The water is not actually part of the
chemical substance and this is reflected in
the way the formula is written.
– BaCl2 . 2 H2O
The Nomeclature of Hydrates
• Example: CuSO4 . 5 H2O
– copper(II) sulfate pentahydrate
Try These
• Na2SO4 .10H2O
– Sodium sulfate decahydrate
• Calcium chloride dihydrate
– CaCl2 . 2H2O
Finding the Empirical Formula
Hydrate Style
• Example #1: A hydrate of magnesium
iodide has a formula MgI2. X H2O. A 1.055
g sample is heated to a constant value of
0.695 g. What is the value of X?
• Step 1: Determine from problem the grams
of H2O and grams of compound (MgI2)
– MgI2 = .695 g
– H2O = .36 g
SOLUTION
• Step 2: Calculate the number of moles of
MgI2 in the final sample:
– Moles MgI2 = .695 g/ (278.1 g/mol) = .0025
moles
• Calculate the number of moles of H2O in
the sample using the molar mass of H2O =
18.02, and the mass of the evaporated
H2O = 0.36 g.
– Moles H2O = .36 g/ (18.02 g/mol) = .020
moles
• Step 3: Divide by the lowest number of
moles (will always be moles of compound,
not water)
.02/.0025 = 8
.0025/.0025 = 1
And the molecular formula is:
MgI2 . 8 H2O
Hydrate Problems
• Practice Problems
Application of Hydrates?
• Methane Hydrate could potentially be a
new energy source. If only one percent of
the methane hydrate resource could be
made technically and economically
recoverable, the United States could more
than double its domestic natural gas
resource.
Global Climate Hazard
• If global warming
occurs, the
temperature will rise
and decompose some
of these methane
hydrates in the
earth. Methane is one
of the most harmful
greenhouse gases and
this effect could be
potentially threatening.
Electronic Equipment?
• Cameras made in Japan are often shipped
to America by ships
• A calcium chloride hydrate is often
packaged with the camera in the box to
absorb moisture so the camera won’t be
damaged.
Bellwork 2/22
• You have a 35.64 g sample of hydrated
barium bromide. The sample is heated to
drive off the water. The dry sample has a
mass of 30.42 g of barium bromide. What
is the formula for the hydrate?
ANSWER TO BELLWORK 2/22
• BaBr2 * 3H2O
Warm-Up 10-23
• Propane is a gas used for cooking and
heating. How many atoms are in 2.12
moles of propane? (Propane = C3H8)
• What is the percent composition of C and
H in propane?
– 1.40 x 1025 atoms
Warm-Up 10-24
• Calculate the mass of 7.89 x 1020 atoms of iron
(Fe).
Warm-Up 10-25-06
• What is the molar mass of NaHCO3?
• How many moles is .346 grams of H2SO4?
• 12.89 moles of Potassium Chloride equals
how many formula units of Potassium
Chloride?