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Mole_Calculations_Presentation Yoos.notebook

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December 04, 2012

Note Book 6Mole Stoichiometry

Calculations

Moles

A single atom has a very small mass. One carbon has a mass of about 2.0 x 1023 grams.

Another unit we can use is an amu (atomic mass unit).One amu is equal to 1/12 the mass of carbon12 or approximately the mass or a proton or neutron

It takes a lot of atoms to give us enough material to directly measure in a lab.

The "mole" is the number of atoms you'd need for the masses in amu on the periodic table be masses in grams.

A single average carbon atom has a mass of 12.01 amu.A mole of carbon has a mass of 12.01 grams.

Moles

How many atoms does it take to convert from a single atomic mass in amu to the same mass in grams?

6.02 x 1023

This is called "Avogadro's Number".

It's just a number...like dozen, ream, etc.

Other Common Quantities1 dozen = 12

1 gross =144

1 ream = 500

1 mole = 6.02 x 1023

Measuring Matter with Moles

The mole 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 x 1023 representative particles.

• The term representative particle refers to the species or types of particles in the substance

For Example: atoms, molecules, formula units, ions

Measuring Matter with Moles How big is a mole?One mole of marbles would cover the entire Earth (oceans included) for a depth of two miles.

If you were able to count at the rate of 1 million numbers a second, it would take about 20 billion years to count out one mole.

1 mole of pennies could be distributed to all the currentlyliving people of the world so that they could spend a million dollars per hour every hour (day and night) for the rest of their lives.


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Avogadro’s Number

• Avogadro's Number is 6.02 x 1023

• In 1 mole of carbon there will be 6.02 x 1023 carbon atoms.

• In 1 mole of water, there will be 6.02 x 1023 water molecules.

• In 1 mole of NaCl, there will be 6.02 x 1023 formula units.

One mole (mol) of a substance is 6.02 x 1023 representative particles of that substance.

The number of representative particles in a mole, 6.02 x 1023, is called Avogadro’s number.

Measuring Matter with Moles

NA = 6.02 x1023 atoms

How many moles of Gold are there in a sample containing 3.01 x 1023 atoms of Gold?

Converting Moles to Number of Particles

FLM• How many apples are there in 3.75 dozen?

3.75 dozen X 12 apples = 45 apples 1 dozen

Unit you are trying to get rid of

Unit you want

1 How many eggs are in two dozen eggs?

A 12B 24C 0.0833

D 2

2 How many eggs are in half a dozen eggs?

A 12B 24C 6D 0.5

3 How many atoms of titanium are in a sample containing 0.5 mole of titanium?

A 1.5 x 1023

B 3.01 x 1023

C 6.02 x 1023

D 1.2 x 1024


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4 How many atoms of sodium are in a sample containing 2.0 moles of sodium?

A 1.5 x 1023

B 3.01 x 1023

C 6.02 x 1023

D 1.2 x 1024

5 How many dozen eggs are in a container of 6 eggs?

A 4

B 0.5

C 1

D 2

6 How many dozen eggs are in container of 18 eggs?

A 1.5B 3C 0.67D 2

7 How many moles of potassium are in a sample containing 3.01 x 1023 atoms of potassium?

A 1.0

B 2.0C 0.5

D 0.75

NA = 6.02 x 1023

8 How many moles of potassium are in a sample containing 1.2 x 1024 atoms of potassium?

B 0.50 mol

C 1.0 mol

D 2.0 mol

E 3.0 mol

A 0.25 mol

NA = 6.02 x 1023

9 How many moles of tungsten atoms are there in a sample containing 1.8 x 1024 atoms of tungsten?

A 0.33 mol

B 0.50 mol

C 1.0 mol

D 1.5 mol

E 3.0 mol

NA = 6.02 x 1023


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December 04, 2012

10 How many moles of silver are there in a pure sample containing 1.5 x 1023 atoms of silver?

A 0.10 mol

B 0.25 mol

C 0.50 mol

D 1.0 mol

NA = 6.02 x 1023

11 How many atoms are there in 5.00 mol of hafnium?

A 6.02 x1023 atoms

B 1.20 x 1023 atoms

C 1.20 x 1022 atoms

D 3.43 x 1023 atoms

E 3.01 x 1024 atoms

NA = 6.02 x 1023

12 How many molecules are there in 2.10 mol CO2?

A 3.79 x 1024

B 3.49 x 1024

C 1.05 x 1023

D 2.53 x 1024

E 1.26 x 1024

NA = 6.02 x 1023

13 How many moles of helium atoms are there in a pure sample containing 6.02 x 1024 atoms of helium?

A 2.0 mol

B 4.0 mol

C 6.0 mol

D 10.0 mol

E 2.4 x 1024 mol

NA = 6.02 x 1023

Converting Moles to Number of Particles

Remember your definitions for atoms, formula units and molecules:

If we have one mole of water molecules...then there are 2 moles of hydrogen atoms and 1 mole of oxygen atoms

molecule of H2O

18.0 amu

Avagadro's number of molecules(6.02 x1023) 1 mol H2O

(18.0 g)

laboratory sample size

H

O

H

14 How many hydrogen atoms are in six molecules of ethylene glycol, the major component in antifreeze?

The formula for ethylene glycol is: HOCH2CH2OH.

A 6 atoms of H

B 36 atoms of H

C 6 x 6.02 x 1023 atoms of H

D 36 x 6.02 x 1023 atoms of H

NA = 6.02 x 1023


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15 How many sulfide ions (S2) are there in 2.0 moles of ammonium sulfide,(NH4)2S?

A 2.0 ions

B 1.2 x 1024 ions

C 2.4 x 1024 ions

D 6.02 x 1023 ions

16 How many ammonium ions (NH4

+) are there in 2.0 moles of ammonium sulfide, (NH4)2S?

A 2.0 ions

B 1.2 x 1024 ions

C 2.4 x 1024 ions

D 6.02 x 10 23 ions

NA = 6.02 x 1023

Molar Mass

Molar mass, measured in grams, can refer to any one of these three things:

• Gram atomic mass used for elements only

• Gram formula mass used for ionic compounds only

• Gram molecular mass used for molecular compounds only

The term "molar mass" can be used in place of any of these three terms.

The symbol for molar mass is "M".

How is the atomic mass of an element related to the molar mass of an element?

The (average) atomic mass of krypton is 83.8 amu.The gram atomic mass of krypton is 83.8 grams.

The atomic mass of an element expressed in grams is the mass of one mole of the element.

Molar Mass

The mass of one mole of an element is its molar mass (M).One mole of carbon, sulfur and silver are shown.

Molar Mass

1 mol of Carbon atoms12.0 g C=1 molar mass C

1 mol of sulfur atoms32.0 g of S=1molar mass S

1 mol of silver107.9 g of Ag= 1 molar mass Ag

17 What is the mass, in grams, of 2 moles of carbon?


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December 04, 2012

18 What is the mass, in grams, of 5 moles of iron?

19 How many grams is 2.0 mol neon atoms?

20 How many moles are in a 64gram sample of pure sulfur?

21 How many moles are in a 72gram sample of pure magnesium?

Diatomic Molecules

Recall the seven diatomic molecules: HONClBrIF.The molar mass of these molecules will be twice their atomic mass.

Examples:

M of hydrogen gas: H2 = (2 x 1)g

M of bromine gas: Br2 = (2 x79.9)g

22 How many grams is 1.0 mole of hydrogen molecules?


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23 How many grams is 0.50 mol of oxygen molecules?

• The molar mass of a compound is the sum of the molar masses of all the elements in the compound.

• Recall that there are two terms which also mean "molar mass" for a compound:

• Gram formula weight used for ionic compounds • Gram molecular weight used for molecular compounds

Molar Mass 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.

Substitute the unit grams instead of atomic mass units. Thus 1 mol of SO3 has a mass of 80.1 g.

Molar Mass of a Compound

SO3

= +

3 O atoms1 S atom

32.1 amu + 16.0 amu + 16.0 amu + 16.0 amu = 80.1 amu

+

Molar Mass of a CompoundNote the different molar masses of these 2 compounds. What do all two samples have in common?

Are these molar masses considered gram atomic masses, gram formula masses, or gram molecular masses?

18 g of H2O = 1 mole H2O180 g of glucose =1 mole glucose

A formula weight is the sum of the atomic weights for the atoms in an ionic compound.

Gram formula mass is the formula weight expressed in grams.

So, the formula weight of calcium chloride, CaCl2, would be:Ca: 1(40.1 amu)

+ Cl: 2(35.5 amu) 111.1 amu

Properly stated:One formula unit of CaCl2 has a formula weight of 111.1 amu.

orOne mole of CaCl2 has a gram formula mass of 111.1 grams.

Formula Weight 24 What is the formula weight of K2O, potassium oxide?

A 94 amu

B 94 grams

C 71 amu

D 71 grams


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December 04, 2012

25 What is the gram formula mass of CaCO3, calcium carbonate found in eggshells?

A 50 amu

B 50 grams

C 100 amu

D 100 grams

A molecular weight is the sum of the atomic weights of the atoms in a molecule.

Gram molecular mass is the molecular weight expressed in grams.

For the molecule ethane, C2H6, the molecular weight would be:

C: 2(12.0 amu)

30.0 amu

+ H: 6(1.0 amu)

Molecular Weight

Properly stated:One molecule of C2H6 has a molecular weight of 30.0 amu.

orOne mole of C2H6 has a gram molecular mass of 30.0 grams.

26 What is the molecular weight of carbon dioxide?

A 28 amu

B 28 grams

C 44 amu

D 44 grams

27 What is the gram molecular mass of ammonia, NH3?

A 17 amu

B 17 grams

C 45 amu

D 45 grams

What is it? Atoms Ionic Compounds

Molecular Compounds

Just one piece has a(n)...

atomic mass(amu)

formula weight(amu)

molecular weight(amu)

One mole of it has a...

gram atomic mass (g)

gram formula mass (g)

gram molecular mass (g)

The short cut term is...

molar mass (g)

Summary of Molar Mass

Molar mass is the mass of 1 mole of a substance (measured in g/mol).

The weight will be the same number as the molar mass (measured in amu).

The difference is that the weight refers to only one representative particle and molar mass refers to one mole (6.02 x 1023) of representative particles.

Summary of Molar Mass


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December 04, 2012

28 The mass of one mole of NaCl is its:

A gram formula mass

B gram molecular mass

C gram atomic mass

D atomic mass

n = Mm

29 The chemical formula of aspirin is C9H8O4. What is the mass of 0.200 moles of aspirin?

n = Mm

30 How many moles of O are in 2.4 X 1024 molecules of SO3?

Mole Road Map

Mole

1mol6.02x10 23 particles

6.02x10 23 particles

1mol

1 mo

l

molar

mass

molar

mass

1 m

ol

1 mol

22.4 L

22.4 L

1 mol

Mass (g)

Volume at STP 22.4L

Representative particles6.02 x1023

31 How many atoms are there in 11.2 liters (at STP) of molecular oxygen ( oxygen gas)?

32 What is the mass of 44.8 liters (at STP) of molecular oxygen?


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33 What is the volume (at STP) of 3.0 x 1023 molecules of fluorine?

34 What is the volume (at STP) of 240 g of bromine gas?

35 How many atoms are present in 30 g of boron ?

36 What is the mass of a pure sample of lead which contains 3.0 x 1024 atoms?

37 How many molecules are in a 32g sample of SO2 ?

A 6 x1023

B 3.0x1023

C 3.0x1024

D 3.0x1024

38 What volume will 5.0x1024 atoms of Oxygen occupy at STP? A 150L

B 186L

C 224L

D 168L


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39 What is the mass of 224L of hexane (C6H12) at STP?

A 74g

B 840g

C 84g

D 420g

40 What is the volume occupied by 6.0x1023 atoms of Hydrogen gas at STP?

A 22.4L

B 11.2L

C 224L

D 112L

Chemical equations describe reactions. When they are balanced, the relationship between what you put in and what you get out can be seen. Here's one.

Vinegar + Baking Soda ⇒ Salt + Water + CO2 Gas

HC2H3O2 + NaHCO3 ⇒ NaC2H3O2 + H2O + CO2

This equation shows that the number of moles of CO2 gas produced will equal the number of moles of HC2H3O2 (baking soda) added (assuming enough vinegar).

The question is: if 10g of baking soda is added to vinegar, what volume of CO2 will be produced?

What would be the diameter of a balloon filled with that much gas?

A Practical Example

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%.

Percent Composition

Potassium chromate, K2CrO4 Potassium dichromate, K2Cr2O7

The percentage, by mass, of an element of a compound can be found by this equation:

% element =(number of atoms)(atomic weight)

(FW of the compound)x 100

Percent Composition

%C = 80.0%

So the percentage of carbon in ethane, (C2H6) is…

%C =(2)(12.0 amu)(30.0 amu)

24.0 amu30.0 amu

= x 100

%H = (6)2.0 30

= 20%

Percent Composition


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December 04, 2012

41 What is the mass percentage of oxygen in water?

A 98

B 78

C 89

D 16

42 What is the percent by mass of carbon in acetone, C3H6O?

A 1.60%

B 62%

C 30.0%

D 20.7%

43 What is the percent of Ba in Ba(NO3)2

A 48%

B 52%

C 55%

D 34%

Calculating Empirical Formulas

One can calculate the empirical formula from the percent composition.

The percent composition of elements in a compound can be determined by analytical instruments.

Empirical formula: The formula that indicates the molar ratio of elements present in a molecular compound reduced to the least common denominator.

For instance, the empirical formula for benzene (C6H6) is CH.

Mass %elements

Grams of each element

Moles ofeach element

Empiricalformula

Assume 100g sample

use molar mass

Calculatemole ratio


Empirical formula: There is only one empirical formula for a substance, but two different substances can have the same empirical formula.

That is because an empirical formula is always based on the ratio of the elements given in their lowest common denominator. For instance:

Substance Molecular EmpiricalFormula Formula

hydrogen peroxide H2O2 OH

hydroxide OH OH

Elemental Analysis by Combustion Analysis

• Compounds containing C, H and O are routinely analyzed through combustion using a combustion analyzer. The compound undergoes combustion reaction producing carbon dioxide and water. The products are traped and collected in different chambers of the instrument.

• C is determined from the mass of CO2 produced.

• H is determined from the mass of H2O produced.

• O is determined by difference after the C and H have been determined.


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December 04, 2012

Elemental Analyses

Compounds containing other elements are analyzed using methods analogous to those used for C, H and O.

44 The empirical formula for C6H4(NO3)2 is C3H2N2O3

True False

45 Which of the following has EF and MF is/are the same? (1) NH4Cl (2) (NH4)2CO3 (3) CH2Cl2 (4) CHCl2Br

A 1 and 3 only

B 1, 2 and 4 only

C 1 and 4 only

D all of them


The compound paraaminobenzoic acid (listed as PABA in bottles of sunscreen) is composed of the following elements (by mass):

carbon (61.31%),

hydrogen (5.14%), nitrogen (10.21%),

and oxygen (23.33%).

Find the empirical formula of PABA.

We first have to convert the mass percentages to mole amounts in a hypothetical 100 g sample. Assume a 100.00 g amount of paraaminobenzoic acid and calculate the moles of each element that would be present.

C: 61.31 g x = 5.105 mol

H: 5.14 g x = 5.09 mol

N: 10.21 g x = 0.7288 mol

O: 23.33 g x = 1.456 mol

1 mol12.01 g

1 mol14.01 g

1 mol1.01 g

1 mol16.00 g


C: 5.105 mol ÷ 0.7288 mol = 7.005 ≈ 7

H: 5.09 mol ÷ 0.7288 mol = 6.984 ≈ 7

N: 0.7288 mol ÷ 0.7288 mol = 1.00 = 1

O: 1.456 mol ÷ 0.7288 mol = 2.001 ≈ 2

Calculating Empirical FormulasCalculate the mole ratio by dividing by the smallest number of moles. In this case, divide all the numbers of moles by that of nitrogen, since in that way they may all be whole numbers...divide them all by 0.7288.


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C: 5.105 mol ÷ 0.7288 mol = 7.005 ≈ 7

H: 5.09 mol ÷ 0.7288 mol = 6.984 ≈ 7

N: 0.7288 mol ÷ 0.7288 mol = 1.00 = 1

O: 1.456 mol ÷ 0.7288 mol = 2.001 ≈ 2


The empirical formula for PABA is C7H7NO2

C: 62.1 g x = 5.17 mol

H: 13.8 g x = 13.7 mol

N: 24.1 g x = 1.72 mol

1,6 diaminohexane is used in making nylon.

It is 62.1% C, 13.8% H and 24.1% N. What is the empirical formula?


1 mol14.01 g

1 mol12 .0 g

1 mol1.0 g


C: 5.17 mol ÷ 1.72 mol = 3.005 ≈ 3

H: 13.7 mol ÷ 1.72 mol = 7.96 ≈ 8

N: 1.72 mol ÷ 1.72 mol = 1.00 = 1

The empirical formula is C3H8N

A molecular formula indicates the number of atoms of each element present in the molecule.

The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple wholenumber multiple of its empirical formula

Molecular Formulas

Formula ( name) Classification of formula

Molar mass

CH Empirical 13

C2H2 ethyne Molecular 26(2 x 13)

C6H6 benzene Molecular 78(6 x 13)

CH2O methanal Empirical and molecular

30

C2H4O2 ethanoic acid

Molecular 60(2 x 30)

C6H12O6 glucose Molecular 180(6 x 30)

To find the actual molecular formula you need one other piece of information...the molecular weight (mass) of the molecule.

If you know the ratio of the elements in a molecule

and you know the total mass of the molecule

then you can determine the molecular formula.

Molecular Formulas46 The molecular mass of

Benzene is 78. If the empirical formula of benzene is CH, what is it's molecular formula?

A C2H2

B CH

C C6H6

D C2H4


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December 04, 2012

Maleic acid is an organic compound composed of 41.39 % carbon, 3.47% hydrogen, and the rest is oxygen. It has a molecular mass of 116 g/mole.

Determine the empirical formula for Maleic acid.Determine the molecular formula for Maleic acid.

Molecular FormulasComplete as many chemical formulas as you can in 4 minutes

Ca2+ + S2 Na + Br Beryllium + Fluorine

magnesium + S

OH + Cadmium (II)

Na+ + SO42 Ba + P Aluminum +

Bromine Chlorine + potassium

potassium + phosphorus

Cl + Sr2+ Cl + Co (II) Manganese (II) + hydroxide

Cu+ + sulfate Calcium + cyanide

F + NH4+ O + K Calcium +

nitrate Ag+ + chlorine

Cesium + F

Ti+2 + P3 Mg + P Barium + sulfite

Chromium (II) + sulfur

Pd+2 + carbonate

Cu+ + NO3 Ni (II) + S Zinc +

phosphate acetate + sodium

NO3 + Zn2+

Mg2+ + I Li + OH Iodine + sodium

bromine + iron (III)

ammonium + chlorate

Complete as many chemical formulas as you can in 4 minutes

CaS NaBr BeF2 MgS Cd(OH)2

Na2SO4 Ba3P2 AlBr3 KCl K3P

SrCl2 CoCl2 Mn(OH)2 Cu2SO4 Ca(CN)2

NH4F K2O Ca(NO3)2 AgCl CsF

Ti3P2 Mg3P2 BaSO3 CrS PdCO3

CuNO3 NiS Zn3(PO4)2 NaC2H3O2 Zn(NO3)2

MgI2 LiOH NaI FeBr3 NH4ClO3

note book 6 - pbworksyooschem1314.pbworks.com/w/file/fetch/73754165/the mole notes… · 1 dozen =...

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