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Chemical QuantitiesChemical Quantitiesoror

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How you measure how much?How you measure how 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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Representative particlesRepresentative particles The smallest pieces of a substance.The smallest pieces of a substance. For an element it is an For an element it is an atomatom..

– Unless it is diatomicUnless it is diatomic For a molecular compound it is a For a molecular compound it is a

moleculemolecule.. For an ionic compound it is a For an ionic compound it is a

formula unitformula unit..

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Conversion factorsConversion factors Used to change units.Used to change units. Three questionsThree questions

– What unit do you want to get rid of?What unit do you want to get rid of?

– Where does it go to cancel out?Where does it go to cancel out?

– What can you change it into?What can you change it into?

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Calculation questionCalculation question How many molecules of COHow many molecules of CO22 are the in are the in

4.56 moles of CO4.56 moles of CO22 ? ?

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Calculation questionCalculation question How many moles of water is 5.87 x 10How many moles of water is 5.87 x 102222

molecules?molecules?

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Calculation questionCalculation question How many atoms of carbon are there in How many atoms of carbon are there in

1.23 moles of C1.23 moles of C66HH1212OO66 ? ?

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Measuring MolesMeasuring Moles The amu was one twelfth the mass of a The amu was one twelfth the mass of a

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

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

table istable is– The mass of the average atom in The mass of the average atom in

amuamu– the mass of 1 mole of those atoms in the mass of 1 mole of those atoms in

grams.grams.

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Gram Atomic MassGram Atomic 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 atoms as 1.01 grams of number of atoms as 1.01 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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ExamplesExamples How much would 2.34 moles of How much would 2.34 moles of

carbon weigh?carbon weigh?

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ExamplesExamples How many moles of magnesium in How many moles of magnesium in

4.61 g of Mg?4.61 g of Mg?

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

two moles of H atoms and 1 mole of two moles of H atoms and 1 mole of O atomsO 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 determine the moles of the

elements they haveelements they have– Find out how much they would Find out how much they would

weighweigh– 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

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Molar MassMolar Mass The mass of 1 moleThe mass of 1 mole What is the molar mass of FeWhat is the molar mass of Fe22OO33??

2 moles of Fe x 55.85 g = 111.70 g2 moles of Fe x 55.85 g = 111.70 g 3 moles of O x 16.00 g = 48.00 g3 moles of O x 16.00 g = 48.00 g The GFM = 111.70 g + 48.00 g = 159.70gThe GFM = 111.70 g + 48.00 g = 159.70g

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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 in 1 mole of The number of grams in 1 mole of

atoms, formula units, or molecules.atoms, formula units, 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. Or moles to gramsOr moles to grams

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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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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, so we’ll They are difficult to weigh, so we’ll

measure volumemeasure volume Need to know how many moles of gas Need to know how many moles of gas

we have.we have. Two things affect the volume of a gasTwo things affect 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

Avogadro's HypothesisAvogadro's Hypothesis - at the same - 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.

0ºC and 1 atmosphere pressure 0ºC and 1 atmosphere pressure Abbreviated atmAbbreviated atm 273 K and 101.3 kPa273 K and 101.3 kPa kPa is kiloPascalkPa is kiloPascal

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AtAt S Standardtandard T Temperatureemperature andand PPressureressure

abbreviated STPabbreviated STP At STP 1 mole of gas occupies 22.4 LAt STP 1 mole of gas occupies 22.4 L Called the Called the molar volumemolar volume Used for conversion factorsUsed for conversion factors Moles to Liter and L to molMoles to Liter and L to mol

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ExamplesExamplesWhat is the volume of 4.59 What is the volume of 4.59

mole of COmole of CO22 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.

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Quizdom 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 Given the density, we can find the

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

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

have 22.4 L of the stuff.have 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?

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All the things we can changeAll the things we can change

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Volume

IonsAtoms

Representative Particles

MassPT

Moles

6.02 x 1023

22.4 L

Count

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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??

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ExamplesExamples What is the percent composition of What is the percent composition of

Aluminum carbonate.Aluminum carbonate.

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Percent to MassPercent to Mass Multiply % by the total mass to find Multiply % by the total mass to find

the mass of that component.the mass of that component. How much aluminum in 450 g of How much aluminum in 450 g of

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 ratio The molecular formula the actual ratio

of elements in a compound.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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Finding Empirical FormulasFinding Empirical Formulas Just find the lowest whole number ratioJust find the lowest whole number ratio CC66HH1212OO66

CHCH44NN22

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.

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Calculating Empirical FormulasCalculating Empirical Formulas 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. Turn grams to moles. Turn grams to moles. Find lowest whole number ratio by Find lowest whole number ratio by

dividing everything by the smallest dividing everything by the smallest moles.moles.

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

compound composed of 38.67 % C, compound composed of 38.67 % C, 16.22 % H, and 45.11 %N.16.22 % 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 = 16.1 mole H 16.22 g H x 1mol H = 16.1 mole H

1.01 gH1.01 gH 45.11 g N x 1mol N = 3.220 mole N 45.11 g N x 1mol N = 3.220 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

3.220 molN 1 3.220 molN 1 mol Nmol N

The ratio is 16.1 mol H = 5 mol HThe ratio is 16.1 mol H = 5 mol H 3.220 molN 1 3.220 molN 1

mol Nmol N

CC11HH55NN11

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

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Empirical to molecularEmpirical to molecular 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?

Since the empirical formula is the lowest Since the empirical formula is the lowest ratio the actual molecule would weigh the ratio the actual molecule would weigh the same or more.same or more.

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

mass of one mole of the empirical formula.mass of one mole of the empirical formula. You will get a whole number.You will get a whole number. Multiply the empirical formula by this.Multiply the empirical formula by this.

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ExampleExample A compound has an empirical

formula of ClCH2 and a molar mass of 98.96 g/mol. What is its molecular formula?

A compound has an empirical formula of CH2O and a molar mass of 180.0 g/mol. What is its molecular formula?

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Percent to molecularPercent to molecular Take the percent x the molar massTake the percent x the molar mass

–This gives you mass in one mole of This gives you mass in one mole of the compoundthe compound

Change this to molesChange this to moles

–You will get whole numbersYou will get whole numbers

–These are the subscriptsThese are the subscripts 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. It has a molar mass of and 16.49% O. It has a molar mass of 194 g. What is its molecular formula?194 g. What is its molecular formula?

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ExampleExample Ibuprofen is 75.69 % C, 8.80 % H, 15.51

% O, and has a molar mass of about 207 g/mol. What is its molecular formula?