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Chapter 11Chapter 11

Chemical QuantitiesChemical QuantitiesChemistryChemistry

Tracy BonzaTracy BonzaSequoyah High SchoolSequoyah High School

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How do you measure how How do you measure how much?much?

You can measure mass, You can measure mass, or volume,or volume, or you can count pieces.or you can count pieces. We measure mass in grams.We measure mass in grams. We measure volume in liters.We measure volume in liters.

We count pieces in We count pieces in MOLES.MOLES.

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MolesMoles Defined as the number of carbon Defined as the number of carbon

atoms in exactly 12 grams of carbon-atoms in exactly 12 grams of carbon-12.12.

1 mole is 6.02 x 101 mole is 6.02 x 102323 particles. particles. Treat it like a very large dozenTreat it like a very large dozen 6.02 x 106.02 x 102323 is called Avogadro's is called Avogadro's

number.number.

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Measuring MolesMeasuring Moles Remember relative atomic mass?Remember relative atomic mass? The amu was one twelfth the mass The amu was one twelfth the mass

of a carbon 12 atom.of a carbon 12 atom. Since the mole is the number of Since the mole is the number of

atoms in 12 grams of carbon-12,atoms in 12 grams of carbon-12, the decimal number on the periodic the decimal number on the periodic

table is also the mass of 1 mole of table is also the mass of 1 mole of those atoms in grams.those atoms in grams.

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Representative particlesRepresentative particles How many oxygen atoms in the How many oxygen atoms in the

following?following?

– CaCOCaCO33

– AlAl22(SO(SO44))33 How many ions in the following?How many ions in the following?

– CaClCaCl22– NaOHNaOH

– AlAl22(SO(SO44))33

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Molar MassMolar Mass The mass of 1 mole of an element in The mass of 1 mole of an element in

grams.grams. 12.01 grams of carbon has the same 12.01 grams of carbon has the same

number of pieces as 1.008 grams of number of pieces as 1.008 grams of hydrogen and 55.85 grams of iron.hydrogen and 55.85 grams of iron.

We can write this as We can write this as 12.01 g C = 1 mole 12.01 g C = 1 mole

We can count things by weighing We can count things by weighing them.them.

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What is the molar mass of:What is the molar mass of: PotassiumPotassium ZincZinc NeonNeon

39g39g 65.4g65.4g 20.2g20.2g

What does that mean?It means that 39g of K is 1 mole of potassium

How many particles of potassium is that?

See…….we can count particles without counting them

……….we weighed them!!!

6.02 x 10 23

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What about compounds?What about compounds? in 1 mole of Hin 1 mole of H22O molecules there are two O molecules there are two

moles of H atoms and 1 mole of O atomsmoles of H atoms and 1 mole of O atoms To find the mass of one mole of a To find the mass of one mole of a

compound compound – determine the moles of the elements determine the moles of the elements

they havethey have– Find out how much they would weighFind out how much they would weigh– add them upadd them up

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What about compounds?What about compounds? What is the mass of one mole of CHWhat is the mass of one mole of CH44??

1 mole of C = 12.01 g1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g4 mole of H x 1.01 g = 4.04g 1 mole CH1 mole CH44 = 12.01 + 4.04 = 16.05g = 12.01 + 4.04 = 16.05g

TheThe Molar mass Molar mass of CHof CH44 is 16.05g is 16.05g The mass of one mole of a molecular The mass of one mole of a molecular

compound.compound.

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Molar MassMolar Mass The generic term for the mass of one The generic term for the mass of one

mole. mole. The same as gram molecular mass (for The same as gram molecular mass (for

molecules/covalent compounds), gram molecules/covalent compounds), gram formula mass (for formula units/ionic formula mass (for formula units/ionic compounds), and gram atomic mass compounds), and gram atomic mass (for atoms).(for atoms).

I will use the generic molar mass I will use the generic molar mass (sometimes I slip up and call it gram (sometimes I slip up and call it gram formula mass so work with me formula mass so work with me here!!!!!)here!!!!!)

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ExamplesExamples Calculate the molar mass of the Calculate the molar mass of the

following and tell me what type it is.following and tell me what type it is. NaNa22SS

NN22OO44

CC

Ca(NOCa(NO33))22

CC66HH1212OO66

(NH(NH44))33POPO44

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Using Molar MassUsing Molar Mass

Finding moles of compoundsFinding moles of compounds

Counting pieces by weighingCounting pieces by weighing

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Molar MassMolar Mass The number of grams of 1 mole of The number of grams of 1 mole of

atoms, ions, or molecules.atoms, ions, or molecules. We can make conversion factors We can make conversion factors

from these.from these. To change grams of a compound to To change grams of a compound to

moles of a compound.moles of a compound.

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g 1 mole

40.00 g

need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g 1 mole

40.00 = 0.142 mol NaOH

g

need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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ExamplesExamples How much would 2.34 moles of How much would 2.34 moles of

carbon weigh, in grams?carbon weigh, in grams? How many moles of magnesium in How many moles of magnesium in

24.31 g of Mg?24.31 g of Mg? How many moles is 4.56 g of COHow many moles is 4.56 g of CO22 ? ?

How many grams is 9.87 moles of How many grams is 9.87 moles of HH22O?O?

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Moles and MoleculesMoles and Molecules 6.02 x 106.02 x 1023 23 =1 mole too!=1 mole too! So we can convert from moles to So we can convert from moles to

molecules too!molecules too!

Try it:Try it: How many molecules are there in 3.6 How many molecules are there in 3.6

moles of sodium hydroxide?moles of sodium hydroxide? How many moles is 3.6x 10How many moles is 3.6x 103434

molecules of gold?molecules of gold?

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3 Step Problems3 Step Problems Converting from grams to Converting from grams to

molecules/atoms and molecules/atoms and molecules/atoms to gramsmolecules/atoms to grams

How many atoms of silver are in How many atoms of silver are in 2.3g of silver?2.3g of silver?

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ExamplesExamples How many molecules in 6.8 g of How many molecules in 6.8 g of

CHCH44??

49 molecules of C49 molecules of C66HH1212OO66 weighs how weighs how

much?much? How many atoms of lithium in 1.00 g How many atoms of lithium in 1.00 g

of Li?of Li? How much would 3.45 x 10How much would 3.45 x 102222 atoms atoms

of U weigh?of U weigh?

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1 Mole

Molar Mass? g

6.02 x 1023

Particles

Molecules

Atoms

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Gases and the MoleGases and the Mole

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GasesGases Many of the chemicals we deal with Many of the chemicals we deal with

are gases.are gases. They are difficult to weigh.They are difficult to weigh. Need to know how many moles of Need to know how many moles of

gas we have.gas we have. Two things effect the volume of a gasTwo things effect the volume of a gas Temperature and pressureTemperature and pressure Compare at the same temp. and Compare at the same temp. and

pressure.pressure.

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Standard Temperature and Standard Temperature and PressurePressure

0ºC and 1 atm pressure0ºC and 1 atm pressure abbreviated STPabbreviated STP At STP 1 mole of gas occupies 22.4 LAt STP 1 mole of gas occupies 22.4 L Called the molar volumeCalled the molar volume Avogadro’s Hypothesis - at the same Avogadro’s Hypothesis - at the same

temperature and pressure equal temperature and pressure equal volumes of gas have the same number volumes of gas have the same number of particles.of particles.

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ExamplesExamples What is the volume of 4.59 mole of What is the volume of 4.59 mole of

COCO22 gas at STP? gas at STP?

How many moles is 5.67 L of OHow many moles is 5.67 L of O2 2 at at

STP?STP? What is the volume of 8.8g of CHWhat is the volume of 8.8g of CH44

gas at STP? gas at STP?

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Density of a gasDensity of a gas D = m /VD = m /V for a gas the units will be g / Lfor a gas the units will be g / L We can determine the density of any We can determine the density of any

gas at STP if we know its formula.gas at STP if we know its formula. To find the density we need the mass To find the density we need the mass

and the volume.and the volume. If you assume you have 1 mole than If you assume you have 1 mole than

the mass is the molar mass (PT)the mass is the molar mass (PT) At STP the volume is 22.4 L.At STP the volume is 22.4 L.

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ExamplesExamples Find the density of COFind the density of CO22 at STP.at STP.

Find the density of CHFind the density of CH44 at STP. at STP.

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The other wayThe other way Given the density, we can find the molar Given the density, we can find the molar

mass of the gas.mass of the gas. Again, pretend you have a mole at STP, Again, pretend you have a mole at STP,

so V = 22.4 L.so V = 22.4 L. m = D x Vm = D x V m is the mass of 1 mole, since you have m is the mass of 1 mole, since you have

22.4 L of the stuff.22.4 L of the stuff. What is the molar mass of a gas with a What is the molar mass of a gas with a

density of 1.964 g/L?density of 1.964 g/L? 2.86 g/L?2.86 g/L?

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All the things we can changeAll the things we can change

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We have learned how toWe have learned how to change moles to gramschange moles to grams moles to atomsmoles to atoms moles to formula unitsmoles to formula units moles to moleculesmoles to molecules moles to litersmoles to liters molecules to atomsmolecules to atoms formula units to atomsformula units to atoms formula units to ionsformula units to ions

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Moles

Mass

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Moles

Mass?g

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Moles

MassVolume ?g

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Moles

MassVolume ?g22.4 L

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Moles

MassVolume

Representative Particles

?g22.4 L

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6.02 x 1023

Moles

MassVolume

Representative Particles

?g22.4 L

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Moles

MassVolume

Representative Particles

6.02 x 1023

?g

Atoms

22.4 L

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Moles

MassVolume

Representative Particles

6.02 x 1023

?g

Atoms molecules

22.4 L

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Percent CompositionPercent Composition Like all percentsLike all percents Part x 100 %Part x 100 %

whole whole Find the mass of each component,Find the mass of each component, divide by the total mass.divide by the total mass.

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ExampleExample Calculate the percent composition of Calculate the percent composition of

a compound that is 29.0 g of Ag with a compound that is 29.0 g of Ag with 4.30 g of S.4.30 g of S.

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Getting it from the formulaGetting it from the formula If we know the formula, assume you If we know the formula, assume you

have 1 mole.have 1 mole. Then you know the pieces and the Then you know the pieces and the

whole.whole.

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ExamplesExamples Calculate the percent composition of Calculate the percent composition of

CC22HH44??

Aluminum carbonate.Aluminum carbonate.

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Empirical FormulaEmpirical Formula

From percentage to formulaFrom percentage to formula

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The Empirical FormulaThe Empirical Formula The lowest whole number ratio of The lowest whole number ratio of

elements in a compound.elements in a compound. The molecular formula the actual The molecular formula the actual

ration of elements in a compound.ration of elements in a compound. The two can be the same. The two can be the same. CHCH22 empirical formula empirical formula CC22HH44 molecular formula molecular formula CC33HH66 molecular formula molecular formula HH22O bothO both

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Calculating EmpiricalCalculating Empirical Just find the lowest whole number ratioJust find the lowest whole number ratio CC66HH1212OO66 CHCH44NN It is not just the ratio of atoms, it is also It is not just the ratio of atoms, it is also

the ratio of moles of atoms.the ratio of moles of atoms. In 1 mole of COIn 1 mole of CO22 there is 1 mole of there is 1 mole of

carbon and 2 moles of oxygen.carbon and 2 moles of oxygen. In one molecule of COIn one molecule of CO22 there is 1 atom there is 1 atom

of C and 2 atoms of O. of C and 2 atoms of O.

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Calculating EmpiricalCalculating Empirical Means we can get ratio from percent Means we can get ratio from percent

composition.composition. Assume you have a 100 g.Assume you have a 100 g. The percentages become grams.The percentages become grams. Can turn grams to moles. Can turn grams to moles. Find lowest whole number ratio by Find lowest whole number ratio by

dividing by the smallest.dividing by the smallest.

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ExampleExample Calculate the empirical formula of a Calculate the empirical formula of a

compound composed of 38.67 % C, 16.22 compound composed of 38.67 % C, 16.22 % H, and 45.11 %N.% H, and 45.11 %N.

Assume 100 g soAssume 100 g so 38.67 g C x 1mol C = 3.220 mole C 38.67 g C x 1mol C = 3.220 mole C

12.01 gC 12.01 gC 16.22 g H x 1mol H = 16.09 mole H 16.22 g H x 1mol H = 16.09 mole H

1.01 gH1.01 gH 45.11 g N x 1mol N = 3.219 mole N 45.11 g N x 1mol N = 3.219 mole N

14.01 gN14.01 gN

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ExampleExample The ratio is 3.220 mol C = 1 mol CThe ratio is 3.220 mol C = 1 mol C

3.219 molN 1 mol N 3.219 molN 1 mol N The ratio is 16.09 mol H = 5 mol HThe ratio is 16.09 mol H = 5 mol H

3.219 molN 1 mol N 3.219 molN 1 mol N

CC11HH55NN11

A compound is 43.64 % P and 56.36 % O. A compound is 43.64 % P and 56.36 % O. What is the empirical formula?What is the empirical formula?

Caffeine is 49.48% C, 5.15% H, 28.87% N Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical and 16.49% O. What is its empirical formula?formula?

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Empirical to molecularEmpirical to molecular Since the empirical formula is the Since the empirical formula is the

lowest ratio the actual molecule lowest ratio the actual molecule would weigh more.would weigh more.

By a whole number multiple.By a whole number multiple. Divide the actual molar mass by the Divide the actual molar mass by the

the mass of one mole of the empirical the mass of one mole of the empirical formula.formula.

Caffeine has a molar mass of 194 g. Caffeine has a molar mass of 194 g. what is its molecular mass?what is its molecular mass?

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ExampleExample A compound is known to be A compound is known to be

composed of 71.65 % Cl, 24.27% C composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar mas is known and 4.07% H. Its molar mas is known (from gas density) is known to be (from gas density) is known to be 98.96 g. What is its molecular 98.96 g. What is its molecular formula?formula?