Ch. 10: Chemical Quantities 10.1 The mole: a measurement of matter Avogadro’s number, mass of a...
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Transcript of Ch. 10: Chemical Quantities 10.1 The mole: a measurement of matter Avogadro’s number, mass of a...
Ch. 10: Chemical Quantities
10.1 The mole: a measurement of matterAvogadro’s number, mass of a mole|
10.2 Mole-mass and mole-volume relationshipsSTP
10.3 Percent composition(skip empirical formulas)
10.1 The Mole: A Measurement of Matter
You could measure the amount of sand in a sand sculpture by counting each grain of sand, but it would be much easier to weigh the sand. You’ll discover how chemists measure the amount of a substance using a unit called a mole, which relates the number of particles to the mass.
10.1
Measuring MatterWhat are three methods for measuring the amount
of something?• You often measure the amount of something by one
of three different methods—by count, by mass, and by volume.
10.1
Sample problem 10.1
Use dimensional analysis:
apples 0.15
1
0.2
12
1
1
90kg
dozen
kg
apples
dozenapples
for Sample Problem 10.1#1 on worksheet
kg5dozen 1
kg 0.2
bushel 2.0
dozen 1bushel 5.0
What is a Mole?– One mole (mol) of a substance is 6.02 1023
representative particles of that substance and is the SI unit for measuring the amount of a substance.
– A mole of any substance contains Avogadro’s number of representative particles, or 6.02 1023 representative particles.
– The term representative particle refers to the species present in a substance: usually atoms, molecules, or formula units.
10.1
What is a Mole?10.1
Sample problem 10.2
Sample Problem 10.2#4 on worksheet
moles 360.0particles10x02.6
mole
1
particles10x17.223
23
On your calculator be sure to put the denominator in parentheses or divide by both 6.02 and 1023
Sample problem 10.3
10.3
Sample Problem 10.3#5 on worksheet
atoms2410x75.2molecule
atoms4mol
molecules2310x02.61mol14.1
The Mass of a Mole of an Element
– The atomic mass of an element expressed in grams is the mass of a mole of the element.
– The mass of a mole of an element is its molar mass.
– Ex. On the periodic table, carbon has a mass of 12.011 amu. We say 12 grams per mole or just 12 grams.
10.1
The Mass of a Mole of an ElementOne molar mass of carbon, sulfur, mercury, and iron are
shown.
10.1
The Mass of a Mole of an Element10.1
The Mass of a Mole of a Compound– To calculate the molar mass of a compound, find
the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound.
10.1
Substitute the unit grams for atomic mass units. Thus 1 mol of SO3 has a mass of 80.1 g.
The Mass of a Mole of a CompoundMolar Masses of Glucose, Water, and Paradichlorobenzene
10.1
Sample problem 10.4
Sample Problem 10.4#7 on worksheet
phosphorus molar mass = 30.974 gchlorine molar mass = 35.453 g
1 mole of phosphorus = 30.974 g3 mole of chlorine = 3 x 35.453 = 106.359 g
molar mass of PCl3 = 30.974 + 106.359 = 137 g/mol
10.1 Section Quiz.
1. Three common ways of measuring the amount of something are by count, by mass, and
a. by temperature.b. by volume.c. by area.d. by density.
10.1 Section Quiz.
2. A mole of hydrogen gas, H2(g), contains 6.02 x 1023 a. molecules.b. atoms.c. amu.d. grams.
10.1 Section Quiz.3. The atomic mass of fluorine is 19.0 amu, so the
molar mass isa. 19.0 amu.b. 19.0 g.c. 6.02 x 1023 amu.d. 6.02 x 1023 g.
10.1 Section Quiz.
4. Calculate the molar mass of ammonium nitrate.a. 45.02 gb. 80.05 gc. 60.06 gd. 48.05 g
NH4NO3
14+4(1)+14+3(16) g
10.2 Mole–Mass and Mole–Volume Relationships
How can you guess the number of jelly beans in a jar? You estimate the size of a jelly bean and then estimate the dimensions of the container to obtain its volume. In a similar way, chemists use the relationships between the mole and quantities such as mass, volume, and number of particles to solve chemistry problems.
10.2
The Mole–Mass Relationship– How do you convert the mass of a substance to
the number of moles of the substance?• Use the molar mass of an element or compound to
convert between the mass of a substance and the moles of a substance.
10.2
Sample problem 10.5
Sample Problem 10.5#9 on worksheet
mass of carbon= 20 x 12.011 = 240.22 gmass of hydrogen = 42 x 1.008 = 42.336 gmass of C20H42 = 282.556 g/mol
g28.1mol
g556.2821
mol310x52.4
Sample problem 10.6
Sample Problem 10.6#11 on worksheet
mol210x42.30342.0g81.10
mol1
g110x70.3
The Mole–Volume Relationship– Avogadro’s hypothesis states that equal volumes
of gases at the same temperature and pressure contain equal numbers of particles.
10.2
The volume of a gas varies with temperature and pressure. Because of these variations, the volume of a gas is usually measured at a standard temperature and pressure.
Standard temperature and pressure (STP) means a temperature of 0°C or 273 K and a pressure of 101.3 kPa (kilopascals) or 1 atmosphere (atm).
The Mole–Volume Relationship
– At STP, 1 mol or, 6.02 1023 representative particles, of any gas occupies a volume of 22.4 L.
– The quantity 22.4 L is called the molar volume of a gas.
10.2
10.7
10.7
Sample Problem 10.7#13 on worksheet
L210x17.70717.0mol
L4.221
mol310x20.3
L9.82mol
L4.221mol70.3
The Mole–Volume Relationship
– Calculating Molar Mass from Density
10.2
Sample problem 10.8
Sample Problem 10.8#15 on worksheet
mol/g2.80mol
L4.22L
g58.3
The Mole Road Map10.2
The Mole Road Map10.2
The Mole Road Map10.2
The Mole Road Map10.2
p. 303 in textbook
10.2 Section Quiz.
1. Calculate the mass in grams of a sample containing 1.85 x 1034 molecules of water.
a. 3.07 x 1010 gb. 5.53 x 1011 gc. 188 gd. 8.46 x 103 g
10.2 Section Quiz.
2. Calculate the number of moles in a spoonful of table sugar (C12H22O11) having a mass of 10.5 g.
a. 32.6 molb. 3.59 103 molc. 3.07 10–3 mold. 1.85 1022 mol
10.2 Section Quiz.
3. What is the volume of 0.35 mol of oxygen gas at STP?
a. 32 Lb. 64 Lc. 7.8 Ld. 16 L
10.3 Percent Composition and Chemical Formulas
It helps to know the percents of the components in a shirt because they affect how warm it is, whether it will need to be ironed, and how it should be cleaned. You will learn how the percents of the elements in a compound are important in chemistry.
10.3
The Percent Composition of a Compound
– Percent Composition from Mass Data• The relative amounts of the elements in a compound
are expressed as the percent composition or the percent by mass of each element in the compound.
The Percent Composition of a Compound• How do you calculate the percent by mass of
an element in a compound?– The percent by mass of an element in a compound is the
number of grams of the element divided by the mass in grams of the compound, multiplied by 100%.
10.3
Sample problem 10.9
Sample Problem 10.9#18 on worksheet
Hg%0.93100xHgO g2.14
Hg g2.13
7.00%Ox100HgO 14.2g
O 1.0g
The Percent Composition of a Compound
Percent Composition from the Chemical Formula
10.3
Sample Problem 10.10#20 on worksheet
nitrogen mass is 14.007 g/molhydrogen mass is 1.008 g/molNH3 mass is 14.007+3(1.008)=17.031 g/mol
N%2.82100xNH g031.17
N g007.14
3
b. NH4NO3
nitrogen mass = 14.007 x 2 = 28.014 ghydrogen mass = 1.008 x 4 = 4.032 goxygen mass = 16.000 x 3 = 48.000 gmass of NH4NO3 = 80.046 g
N%0.35100xNONH g046.80
N g014.28
34
The Percent Composition of a Compound• You can use percent composition to calculate the number of
grams of any element in a specific mass of a compound.
– Propane (C3H8) is 81.8% carbon and 18% hydrogen. You can calculate the mass of carbon and the mass of hydrogen in an 82.0 g sample of C3H8.
10.3
Empirical Formulas
• The empirical formula gives the lowest whole-number ratio of the atoms of the elements in a compound.– The empirical formula of a compound shows the
smallest whole-number ratio of the atoms in the compound.
10.3
Empirical Formulas
• Ethyne (C2H2) is a gas used in welder’s torches. Styrene (C8H8) is used in making polystyrene.
• These two compounds of carbon have the same empirical formula (CH) but different molecular formulas.
10.3
Molecular Formulas10.3
Methanal, ethanoic acid, and glucose all have the same empirical formula—CH2O.
1. Calculate the percent by mass of carbon in cadaverine, C5H14N2, a compound present in rotting meat. a. 67.4% Cb. 58.8% Cc. 51.7% Cd. 68.2% C
10.3 Section Quiz.
10.3 Section Quiz.
3. Determine the molecular formula of a compound that contains 40.0 percent C, 6.71 percent H, and 53.29 percent O and has a molar mass of 60.05 g.
a. C2H4O2
b. CH2O
c. C2H3O
d. C2H4O
Ch. 10—What you need to know• Ch. 10 worksheet problems—Converting using Avogadro’s number, molar mass, and molar
volume• Who is Counting? Lab• % Composition of a Penny Lab• Measure by count, mass, volume• Avogadro’s number, mole, representative particles• Atomic mass, molar mass, molar volume• Mole-mass, mole-volume relationships• STP (standard temperature and pressure; 0º C or 273 K and 101.3 kPa or 1 atm)• Pa is a unit of pressure--pascals• Mole—SI unit of measure for amount of a substance• Percent composition
• The majority of the quiz is calculations. Be able to show work using dimensional analysis (“railroad tracks”) and include units.