Transcript Moles,_Particles,_Mass,_Formulas

The Mole
Q: how long would it take to spend a mole of $1 coins if
they were being spent at a rate of 1 billion per second?
Measuring the Amount of “Stuff”
• Suppose you needed to measure the amount
of sand in a child’s sandbox…
– You could count each grain of sand (the
number of particles)
– You could weigh the sand (mass)
– You could measure how many bucket-fulls
of sand there are (volume)
– You could use moles to convert the
number of particles to mass or to volume
and vice versa
1 Mole = 6.02 x
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23
10
particles
Defining particles…
Elements have particles called Atoms
Compounds have particles called Molecules
Moles are like measuring cups
Mollionaire
Q: how long would it take to spend a mole of
$1 coins if they were being spent at a rate of
1 billion per second?
A: $ 6.02 x 1023 / $1 000 000 000
= 6.02 x 1014 payments = 6.02 x 1014 seconds
6.02 x 1014 seconds / 60 = 1.003 x 1013 minutes
1.003 x 1013 minutes / 60 = 1.672 x 1011 hours
1.672 x 1011 hours / 24 = 6.968 x 109 days
6.968 x 109 days / 365.25 = 1.908 x 107 years
A: It would take 19 million years
Comparing sugar (C12H22O11) & H2O
Same
1 gram each
1 mol each
No, they have dif. No, molecules
volume?
densities.
have dif. sizes.
Yes, that’s what
No, molecules
mass?
grams are.
have dif. masses
No, they have dif.
Yes.
# of moles? molar masses
No, they have dif. Yes (6.02x1023
# of
in each)
molecules? molar masses
No, sugar has
# of atoms?
No
more (45:3 ratio)
Example: How many moles of
23
magnesium is 1.25 x 10 atoms
of magnesium?
• 1 mole Mg = 6.02 x 1023 atoms Mg
• Use as a conversion factor in a t-table
= 2.08 x 10-1 mol Mg
Round Table Practice
1. What is Avogadro’s Number?
2. How many moles of sodium is 6.482 x 1023 atoms of
sodium?
3. If there are 1.03 x 105 mol cesium, then how many
atoms are there?
4. If there are 8.925 x 10-3 mol of sulfur, then how many
atoms are there?
5. How many atoms are in 2.12 mol of propane (C3H8)?
6. You have 1.14 mol SO3. a)What is the name of this
compound. b) How many atoms are there?
7. a) How many moles are there in 4.65 x 1024 molecules
of NO2 b)What is the name of this compound?
Answers to Round Table Practice
6.02 x 1023 particles of a substance
1.08 x 1010 mol Na
6.20 x 1028 atoms Cs
5.37 x 1021 atoms S
1.40 x 1025 atoms in this sample of
propane
6. a) sulfur trioxide, b) 2.75 x 1024 atoms
7. a) 7.72 mol NO2 b) nitrogen dioxide
1.
2.
3.
4.
5.
Homework Assignment
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Section 10.1 wksht,
9-14 pg. 296
3-4 pg. 291
5-6 pg. 292
Finish Naming Compounds Review
Molar Mass – Use the Periodic Table
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The mass of one mole is called “molar mass”
Example: 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S 32.06 g/mol SO2 64.06 g/mol
Cu3(BO3)2 308.27 g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
Cu x 3 = 63.55 x 3 = 190.65
(NH4)2CO3 B x 2 = 10.81 x 2 = 21.62
O2
O x 6 = 16.00 x 6 = 96.00
308.27
Pb3(PO4)2
C6H12O6
Molar mass
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The mass of one mole is called “molar mass”
E.g. 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S 32.06 g/mol SO2 64.06 g/mol
Cu3(BO3)2 308.27 g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
110.98 g/mol (Cax1, Clx2)
(NH4)2CO3 96.11 g/mol (Nx2, Hx8, Cx1, Ox3)
O2
32.00 g/mol (Ox2)
Pb3(PO4)2 811.54 g/mol (Pbx3, Px2, Ox8)
C6H12O6 180.18 g/mol (Cx6, Hx12, Ox6)
Molar Mass – Don’t be fooled by
other names!
• Gram Atomic Mass (GAM) – molar mass
of an element (all atoms are identical)
• Gram Molecular Mass (GMM) – molar
mass of a compound (atoms that are
covalently bonded)
• Gram Formula Mass (GFM) molar mass of
an ionic compound (ions bound in specific
simple mole ratios)
Converting between grams and moles
• If we are given the # of grams of a compound
we can determine the # of moles, & vise-versa
• In order to convert from one to the other you
must first calculate molar mass
• Use a t-table to decide which conversion factor to
use.
Formula
HCl
H2SO4
NaCl
Cu
g/mol
36.46
98.08
58.44
63.55
g
mol (n)
9.1
0.25
53.15 0.5419
207
3.55
1.27 0.0200
Homework Assignment
• 10.2 wksht (mole mass problems – we’ll
finish the rest tomorrow)
• 7,8,15 pg. 296
• 18-19 pg. 299
• 24, 26, 27 pg. 303
Mole Mass Practice Problems
1. How many moles are represented by 16.0 g of
ethanol, C2H5OH?
2. How many grams of glucose are in 6.63 x 1023
molecules of glucose, C6H12O6?
3. How many moles of methanol, CH3OH, are in
6.53 x 1023 molecules of methanol?
4. How many moles of sodium chloride are in 16.0 g of
sodium chloride?
5. How many molecules, of potassium hydroxide are in
40.6 g?
6. How many grams of chromic chloride are in 7.14
moles of chromic chloride?
Volume of a Mole of Gas
• Volume varies with a change in temperature of
pressure
• The volume of a gas is usually measured at
Standard Temperature and Pressure, STP
• Standard Temperature: 0 C
• Standard Pressure: 101.3 kPa or 1 atm
• At STP, 1 mole of any gas fills 22.4 L (molar
volume of a gas)
• 22.4 L of a gas at STP has 6.02 x 1023 particles
Molar Density
• Density =
Mass . = grams .
Volume
milliliters
• Molar Density will always have the same t-table
except for the first square
Example Problems
• Humans take in oxygen to burn glucose and
gain energy. The water and carbon dioxide
produced in this reaction, called cellular
respiration, are exhaled.
– If 28 g of water is produced in this reaction,
what volume of water vapor could be exhaled?
– How many atoms are exhaled if 44.8 L of CO2
is released?
– How many grams of oxygen is consumed in the
reaction if the volume of oxygen inhaled was
250.0 mL?
Homework Assignment
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Finish 10.2 wksht
20-21 pg. 301
22-23 pg. 302
25, 28-31 pg. 303
Percent Composition: The relative
amounts of each element in a compound
expressed as a percent
• Also called “percent by mass”
• % means “part over whole”
• Example: 8.2 g of Magnesium reacts
completely with 5.40 g of Oxygen to form a
compound. What is the percent composition of
each element in the compound?
Solution
• Mass of MgO = 8.2 g + 5.40 g = 13.60 g
• (because the law of conservation of mass is
ALWAYS true)
If all you are given is the formula or name
of a compound, then you must use Molar
Mass from the Periodic Table
• Example: Calculate the % composition of
propane, C3H8.
• Molar mass of C3H8 = 44.0 g/mol
• Mass of carbon = 3 x 12 = 36 g/mol
• Mass of hydrogen = 8 x 1 = 8 g/mol
Percent Composition can also be used
as a conversion to solve for mass.
• Calculate the mass of carbon in 82.0 g of propane
C3H8
• Molar mass of C3H8 = 44 g/mol
• Mass of carbon = 3 x 12 = 36 g/mol
• %C in propane = 81.8%... So if there were 100 g
of propane, 81.8g would be C
= 67.1 g of C
Empirical and Molecular Formulas
Consider NaCl (ionic) vs. H2O2 (covalent)
Na Cl Na Cl
Cl Na Cl Na
• Chemical formulas are either “simplest”
(a.k.a. “empirical”) or “molecular”. Ionic
compounds are always expressed as
simplest whole number ratios, or formula
units.
• Covalent compounds can either be
molecular formulas (H2O2) or empirical
formulas (HO)
Steps to Calculate the Empirical Formula
• What is the empirical formula of a compound that is
25.9% nitrogen and 74.1% oxygen?
1. Assume that the % given is equal to the number of
grams.
N = 25.9 g
O = 74.1 g
2. Convert the number of grams to moles using GAM.
3. Divide by the lowest number of moles to
obtain the simplest whole number ratio
4. If necessary, multiply by a whole number to
obtain a whole-number ratio
1 mol N x 2 = 2 mol N
2.5 mol O x = 5 mol O
5. Write the chemical formula using these whole
number ratios
N2O5
• Q - Write empirical formulas for propene
(C3H6), ethene (C2H2), glucose (C6H12O6),
octane (C8H14)
• Q - Identify these as empirical formula,
molecular formula, or both H2O, C4H10, CH,
NaCl
Answers
Q - Write simplest formulas for propene (C3H6),
C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecular
formula, or both H2O, C4H10, CH, NaCl
A - CH2 CH CH2O
C 4H 7
A - H2O is both simplest and molecular
C4H10 is molecular (C2H5 would be simplest)
CH is simplest (not molecular since CH can’t
form a molecule - recall Lewis diagrams)
NaCl is simplest (it’s ionic, thus it doesn’t
form molecules; it has no molecular formula)
Determine the Molecular Formula
• You must know the empirical formula.
• You must also know the molar mass of the compound.
• Divide the molar mass of the compound by the
empirical formula mass
• Example: Calculate the molecular formula of a
compound whose molar mass is 60.0 g and empirical
formula is CH4N.
• CH4N = 30 g/mol (using periodic table)
• ? = 60 g/mol
• Need twice as much… multiply subscripts in chemical
formula by two
• CHN
Homework Assignment
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10.3 wksht
32-33 pg. 306
34-35 pg. 307
36-37 pg. 310
38-39 pg. 312
Pre-Lab Digenite Lab
Digenite Lab – Choose Your Role
• Alchemist – measures out materials,
combines them, and heats them up
• Mathematician – guides team through the
calculations and provides calculatorsupport
• Troubadour – tells the story of the lab
through careful and detailed observations
• Scribe – records team data on the class data
table and ensures accurate information is
recorded by each team member