Chapter Chapter 1010

Chemical Chemical QuantitiesQuantities

Molar MassMolar Mass MOLAR MASS—# of grams of an element in MOLAR MASS—# of grams of an element in

one mole of that element. one mole of that element.

= atomic mass of an element with the units = atomic mass of an element with the units of g/molof g/mol

Get it from the periodic table Get it from the periodic table

Elements

Compounds ADD the molar

mass of every atom present in the compound

Find the molar mass on the periodic table round to

0.1 g/mol

Molar Mass

MOLAR MASS MOLAR MASS PRACTICEPRACTICE

If you know the If you know the MOLAR MASS MOLAR MASS …… You can convert between You can convert between grams and molesgrams and moles! !

1 Mole

Mass

Volumeof gas at STP

Representative Particles

Molar mass (g/mol)

Mole ↔ Mass ExamplesMole ↔ Mass Examples How many moles in 51.0 g of How many moles in 51.0 g of Na3PO4??

Find Molar Mass: (23.0 x 3) + 31.0 + (16.0 x 4)

= 164 g/mol 51.0 g Na3PO4 x 1 mole Na3PO4= 0.311 mol Na3PO4

164 g Na3PO4

What is the mass of 0.70 mol of What is the mass of 0.70 mol of NH4Cl?? Find Molar Mass: 14.0 + (1.0 x 4) + 35.5

= 53.5g/mol 0.70 mol NH4Cl x 53.5 g NH4Cl = 37.45 g NH4Cl

1 mol NH4Cl

If you know If you know Avogadro’s numberAvogadro’s number …… You can convert between You can convert between particles and particles and

molesmoles! !

1 Mole

Mass

Volumeof gas at STP

Representative Particles

Avogadro’s Number

6.02 x 10 23 Molar mass (g/mol)

Atoms – elementsFormula Units - ionic Molecules - covalent

A mole = Avogadro’s # = 6.02x1023 representative particles

By COUNT:By COUNT:

By COUNT: Avogadro's NumberBy COUNT: Avogadro's NumberHow big is 6.02x10How big is 6.02x102323??

602 000 000 000 000 000 000 000602 000 000 000 000 000 000 000

If you had Avogadro's number of If you had Avogadro's number of un-popped popcorn kernels, and un-popped popcorn kernels, and spread them across the United spread them across the United States of America, the country States of America, the country would be covered in popcorn to a would be covered in popcorn to a depth of over 9 miles. depth of over 9 miles.

If we were able to count atoms at If we were able to count atoms at the rate of 10 million per second, it the rate of 10 million per second, it would take about 2 billion years to would take about 2 billion years to count the atoms in one mole. count the atoms in one mole.

A mole of coke cans would cover A mole of coke cans would cover the surface of the earth to a depth the surface of the earth to a depth of over 200 miles. of over 200 miles.

Measuring Measuring MatterMatter Some units of measurement indicate specific Some units of measurement indicate specific

numbers.numbers. A pair means 2A pair means 2 A dozen means 12A dozen means 12

Knowing how count, mass, & volume relate Knowing how count, mass, & volume relate allows you to convert between them.allows you to convert between them.

If 1 dozen apples = 12 apples, and 1 dozen If 1 dozen apples = 12 apples, and 1 dozen apples has a mass of 2.0 kg, What is the mass apples has a mass of 2.0 kg, What is the mass of 90 apples?of 90 apples?

90/12 = 7.5 dozen 7.5 dozen x 2.0 kg 90/12 = 7.5 dozen 7.5 dozen x 2.0 kg = 15 kg= 15 kg

What is a Mole?What is a Mole? When dealing with tiny particles (atoms, When dealing with tiny particles (atoms,

ions, compounds), the sample size is ions, compounds), the sample size is usually very large.usually very large.

Counting is not practical.Counting is not practical. Just as a dozen eggs represents 12 Just as a dozen eggs represents 12

eggs, a eggs, a molemole (mol) of a substance (mol) of a substance represents 6.02 x 10represents 6.02 x 102323 representative representative particles of that substance.particles of that substance.

The number 6.02 x 10The number 6.02 x 102323 is known as is known as Avogadro’s numberAvogadro’s number

The MoleThe Mole A A representative particlerepresentative particle tells the type of tells the type of

particle: atoms, molecules, or formula unitsparticle: atoms, molecules, or formula units 1 mole of nitrogen gas (N1 mole of nitrogen gas (N22) contains ) contains

6.02 x 106.02 x 102323 molecules. molecules. Because NBecause N2 2 is a moleculeis a molecule

1 mole of calcium fluoride (CaF1 mole of calcium fluoride (CaF22) )

contains 6.02 x 10contains 6.02 x 102323 formula units formula units Because CaFBecause CaF22 is an ionic compound, and the is an ionic compound, and the

representative particle is the formula unit.representative particle is the formula unit. How many atoms of He are in 1 mole?How many atoms of He are in 1 mole?

MolesMoles Determining the number of atoms in a Determining the number of atoms in a

mole of a compound:mole of a compound: How many moles are in a representative How many moles are in a representative

particle (formula unit or molecule) of the particle (formula unit or molecule) of the substance?substance? This can be determined from the formula.This can be determined from the formula.

Example:Example: each molecule of CO each molecule of CO22 contains 3 contains 3

atoms: 1 carbon atom and 2 oxygen atoms.atoms: 1 carbon atom and 2 oxygen atoms. A mole of COA mole of CO22 contains 1 mole of carbon contains 1 mole of carbon

atoms and 2 moles of oxygen atoms.atoms and 2 moles of oxygen atoms.

The Mass of a The Mass of a MoleMole When dealing with atoms, it is often When dealing with atoms, it is often

easier to work with mass.easier to work with mass. Gram atomic mass (gam)Gram atomic mass (gam)—the —the

atomic mass of an element expressed atomic mass of an element expressed in grams.in grams. The atomic mass of carbon is 12 amuThe atomic mass of carbon is 12 amu The The gamgam of carbon is 12 g. of carbon is 12 g.

The The gamgam is the mass of 1 mole of is the mass of 1 mole of atoms of any element.atoms of any element.

The Mass of a Mole of a The Mass of a Mole of a CompoundCompound

To determine the mass of a mole of a To determine the mass of a mole of a compound you need to know the formula and compound you need to know the formula and the the gamgam of each atom in the compound. of each atom in the compound. Add the masses of each atom to get the mass of Add the masses of each atom to get the mass of

the compoundthe compound Sulfur trioxide (SOSulfur trioxide (SO33))

1 mole of S (32.1g) & 3 moles of O (16.0 g each)1 mole of S (32.1g) & 3 moles of O (16.0 g each) 32.1g + 16.0g + 16.0g + 16.0g = 80.1 g32.1g + 16.0g + 16.0g + 16.0g = 80.1 g

Gram molecular mass (gmm)Gram molecular mass (gmm)—the mass of —the mass of 1 mole of a molecular compound1 mole of a molecular compound

Gram formula mass (gfm)Gram formula mass (gfm)—the mass of 1 —the mass of 1 mole of an ionic compoundmole of an ionic compound

Sec. 2 Mole-Mass-Sec. 2 Mole-Mass-VolumeVolume We learned about We learned about gamgam, , gmmgmm, & , & gfmgfm last last

time. We can use 1 broad term to tell the time. We can use 1 broad term to tell the mass of a substance.mass of a substance.

Molar MassMolar Mass—the mass (in grams) of 1 mole —the mass (in grams) of 1 mole of a substance.of a substance. Why do we have the 3 terms then?Why do we have the 3 terms then? Sometimes Sometimes

the term the term molar massmolar mass in unclear. in unclear. What is the What is the molar mass of oxygen?molar mass of oxygen? Do you mean oxygen Do you mean oxygen gas (Ogas (O22)? Then the molar mass is 32.0g (2 x )? Then the molar mass is 32.0g (2 x

16.0g). Or do you mean oxygen atoms (O)? 16.0g). Or do you mean oxygen atoms (O)? Then the molar mass is 16.0 g.Then the molar mass is 16.0 g.

The Volume of a The Volume of a Mole of GasMole of Gas The volumes of 1 mole of different solid and The volumes of 1 mole of different solid and

liquid substances are not the same.liquid substances are not the same. The volumes of 1 mole of different The volumes of 1 mole of different gasesgases are are

the same under the same conditions.the same under the same conditions. To keep things under the same conditions, To keep things under the same conditions,

gases are measured at standard temperature gases are measured at standard temperature and pressure (STP)and pressure (STP)

Standard temp is 0Standard temp is 0°C°C Standard pressure is 101.3kPa (or 1 atm)Standard pressure is 101.3kPa (or 1 atm) At STP, 1 mole of any gas has a volume of At STP, 1 mole of any gas has a volume of

22.4 L22.4 L

Converting Between Converting Between moles, particles, mass, moles, particles, mass,

and volumeand volume

Mole

Mass

Volumeof gas at STP

Representative Particles

Molar mass1 mol

1 mol . molar mass

1 mol 22.4 L

22.4 L1 mol

6.02 x 1023 particles1 mol

1 mol .6.02 x 1023 particles

Note: to convert between particles, mass, and volume, you have to go through moles.

Sec. 3: Percent Sec. 3: Percent Composition & Chemical Composition & Chemical

FormulasFormulas Percent CompositionPercent Composition—The relative amount —The relative amount of each element in a compoundof each element in a compound The % of all elements in the compound must The % of all elements in the compound must

equal 100%equal 100% % mass of element =% mass of element = grams of element grams of element x 100 x 100

grams of compoundgrams of compound OrOr

% mass of element =% mass of element = molar mass of element molar mass of element x 100 x 100molar mass of compoundmolar mass of compound

ExampleExample An 8.20 g piece of magnesium combines An 8.20 g piece of magnesium combines

completely with 5.40 g of oxygen to form a completely with 5.40 g of oxygen to form a compound. What is the % composition?compound. What is the % composition?

First—add 8.20 g & 5.40 g to get the mass of First—add 8.20 g & 5.40 g to get the mass of the compound. 8.20 + 5.40 = 13.60 gthe compound. 8.20 + 5.40 = 13.60 g

% Mg = (mass of Mg/mass of compound) % Mg = (mass of Mg/mass of compound) x 100x 100 % Mg = 8.20g/13.60g x 100 = 60.3%% Mg = 8.20g/13.60g x 100 = 60.3%

% O = (mass of O / mass of compound) x 100% O = (mass of O / mass of compound) x 100 % O = 5.40/13.60 x 100 = 39.7%% O = 5.40/13.60 x 100 = 39.7%

Does this make sense? Does this make sense? 60.3 + 39.7 = 10060.3 + 39.7 = 100

Empirical FormulasEmpirical Formulas Empirical formulaEmpirical formula—gives the lowest whole-—gives the lowest whole-

number ratio of the elements in a compoundnumber ratio of the elements in a compound An empirical formula may or may not be the An empirical formula may or may not be the

same as a molecular formula.same as a molecular formula. If the formulas are different, the molecular formula If the formulas are different, the molecular formula

is a simple multiple of the empirical formula.is a simple multiple of the empirical formula. Examples:Examples:

The empirical formula for HThe empirical formula for H22OO22 is HO is HO For COFor CO22, the empirical & molecular formula are , the empirical & molecular formula are

the same.the same. CC66HH66 and C and C22HH22 have the same empirical formula: have the same empirical formula:

CHCH

Molecular Molecular FormulasFormulas You can determine the molecular You can determine the molecular

formula if you know empirical formula formula if you know empirical formula and molar mass.and molar mass.

Divide the molar mass by the empirical Divide the molar mass by the empirical formula mass.formula mass.

Multiply this number by all subscripts in Multiply this number by all subscripts in the empirical formula to get the the empirical formula to get the molecular formula.molecular formula.

Example:Example: Find molecular formula with a molar mass of Find molecular formula with a molar mass of

60.0g and empirical formula of CH60.0g and empirical formula of CH44NN

11stst find the empirical formula mass find the empirical formula mass 1 C, 4 H, 1 N1 C, 4 H, 1 N 12 + (4 x 1) + 14 = 30 g12 + (4 x 1) + 14 = 30 g

Then, divide molar mass by empirical massThen, divide molar mass by empirical mass 60.0g / 30 g = 260.0g / 30 g = 2

Multiply each element subscript by the this.Multiply each element subscript by the this. CC22HH88NN22

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