Transcript Chapter 7 Chemical Quantities
1 Section 3.3
The Mole: A Measurement of Matter OBJECTIVES: –
Describe how Avogadro’s number is related to a mole of any substance.
2 Section 3.3
The Mole: A Measurement of Matter OBJECTIVES: –
Calculate the mass of a mole of any substance.
3 What is a Mole?
You can measure mass ,
or volume ,
or you can count pieces .
We measure mass in grams.
We measure volume in liters.
We count pieces in MOLES.
4 Moles (abbreviated: mol)
Defined as the number of carbon atoms in exactly 12 grams of carbon-12.
1 mole is 6.02 x 10 23 particles.
Treat it like a very large dozen
6.02 x 10 23 number.
is called Avogadro’s
5 Representative particles
The smallest pieces of a substance.
–
For a molecular compound: it is the molecule.
–
For an ionic compound: it is the formula unit.
–
For an element: it is the atom.
Types of questions
How many molecules of CO 2 there in 4.56 moles of CO 2 ?
are
How many moles of water is 5.87 x 10 22 molecules?
6
How many atoms of carbon are there in 1.23 moles of C 6 H 12 O 6 ?
How many moles is 7.78 x 10 24 formula units of MgCl 2 ?
7 Measuring Moles
Remember relative atomic mass?
The amu was one twelfth the mass of a carbon-12 atom.
Since the mole is the number of atoms in 12 grams of carbon-12,
the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.
Gram Atomic Mass (gam)
Equals the mass of 1 mole of an element in grams
12 grams of C has the same number of pieces as 1 gram of H and 56 grams of iron.
We can write this as 12 g C = 1 mole C
8
We can count things by weighing them.
9 Examples
How much would 2.34 moles of carbon weigh?
How many moles of magnesium is 24 g of Mg?
How many atoms of lithium is 1.00 g of Li?
How much would 3.45 x 10 22 of U weigh?
atoms
What about compounds?
in 1 mole of H 2 O molecules there are two moles of H atoms and 1 mole of O atoms
To find the mass of one mole of a compound
–
determine the moles of the elements they have
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Find out how much they would weigh
–
add them up
10
What about compounds?
11
What is the mass of one mole of CH 4 ?
1 mole of C = 12 g 4 mole of H x 1 g = 4 g 1 mole CH 4 = 12 + 4 = 16 g
The Gram Molecular Mass (gmm) of CH 4 is 16 g
–
this is the mass of one mole of a molecular compound.
12 Gram Formula Mass (gfm)
The mass of one mole of an ionic compound.
Calculated the same way as gmm.
What is the GFM of Fe 2 O 3 ?
2 moles of Fe x 56 g = 112 g 3 moles of O x 16 g = 48 g The GFM = 112 g + 48 g = 160 g
13 Section 3.3
Mole-Mass and Mole-Volume Relationships OBJECTIVES: –
Use the molar mass to convert between mass and moles of a substance.
14 Section 3.3
Mole-Mass and Mole-Volume Relationships OBJECTIVES: –
Use the mole to convert among measurements of mass, volume, and number of particles.
15 Molar Mass
Molar mass is the generic term for the mass of one mole of any substance (in grams)
The same as: 1) gram molecular mass, 2) gram formula mass, and 3) gram atomic mass- just a much broader term.
Examples 16
Calculate the molar mass of the following and tell what type it is:
Na 2 S
N 2 O 4
C
Ca(NO 3 ) 2
C 6 H 12 O 6
(NH 4 ) 3 PO 4
17 Molar Mass
The number of grams of 1 mole of atoms, ions, or molecules.
We can make conversion factors from these.
–
To change grams of a compound to moles of a compound.
18 For example
How many moles is 5.69 g of NaOH?
19 For example
How many moles is 5.69 g of NaOH?
g
20 For example
How many moles is 5.69 g of NaOH?
g mole
g
need to change grams to moles
21 For example
How many moles is 5.69 g of NaOH?
g mole
g
need to change grams to moles
for NaOH
For example 22
How many moles is 5.69 g of NaOH?
g mole
g
need to change grams to moles
for NaOH
1mole Na = 23 g 1 mol O = 16 g
1 mole of H = 1 g
For example
How many moles is 5.69 g of NaOH?
g mole
g
need to change grams to moles
for NaOH
1mole Na = 23 g 1 mol O = 16 g
1 mole of H = 1 g
23
1 mole NaOH = 40 g
For example
How many moles is 5.69 g of NaOH?
g 1 mole 40.00
g
need to change grams to moles
for NaOH
1mole Na = 23 g 1 mol O = 16 g
1 mole of H = 1 g
24
1 mole NaOH = 40 g
For example
How many moles is 5.69 g of NaOH?
g 1 mole 40.00
g
= 0.142 mol NaOH
need to change grams to moles
for NaOH
1mole Na = 23 g 1 mol O = 16 g
1 mole of H = 1 g
25
1 mole NaOH = 40 g
26 Examples
How many moles is 4.56 g of CO 2 ?
How many grams is 9.87 moles of H 2 O?
How many molecules is 6.8 g of CH 4 ?
49 molecules of C 6 H 12 O 6 how much?
weighs
Gases 27
Many of the chemicals we deal with are gases.
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They are difficult to weigh.
Need to know how many moles of gas we have.
Two things effect the volume of a gas
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Temperature and pressure
We need to compare them at the same temperature and pressure.
28 Standard Temperature and Pressure
0ºC and 1 atm pressure
abbreviated STP
At STP 1 mole of gas occupies 22.4 L
Called the molar volume
1 mole = 22.4 L of any gas at STP
29 Examples
What is the volume of 4.59 mole of CO 2 gas at STP?
How many moles is 5.67 L of O 2 at STP?
What is the volume of 8.8 g of CH 4 gas at STP?
Density of a gas
D = m / V
–
for a gas the units will be g / L
We can determine the density of any gas at STP if we know its formula.
To find the density we need the mass and the volume.
If you assume you have 1 mole, then the mass is the molar mass (from PT)
30
At STP the volume is 22.4 L.
31 Examples
Find the density of CO 2 at STP.
Find the density of CH 4 at STP.
The other way
Given the density, we can find the molar mass of the gas.
Again, pretend you have 1 mole at STP, so V = 22.4 L.
m = D x V
m is the mass of 1 mole, since you have 22.4 L of the stuff.
What is the molar mass of a gas with a density of 1.964 g/L?
32
2.86 g/L?
Summary 33
These four items are all equal: a) 1 mole b) molar mass (in grams) c) 6.02 x 10 23 particles representative d) 22.4 L at STP Thus, we can make conversion factors from them.