2.c – conserving matter. 2c.1- keeping track of atoms

2.C – Conserving Matter

2C.1- Keeping Track of Atoms

When a car’s gas empties, where do the atoms in the gasoline go?

Keeping Track of Atoms Law of Conservation of Matter: Matter is

neither created nor destroyed.

Since chemical reactions cannot create or destroy atoms, chemical equations representing the reactions must always be BALANCED.

Atomic Perspective:

C O2 CO2

1 Carbon atom 1 oxygen molecule 1 carbon dioxide molecule

1. What are the reactants in this chemical equation?

2. What are the products in this chemical equation?

3. Are there the same number of atoms on both sides of the equation?

a. Where any atoms destroyed or created?

b. Was the Law of Conservation of Matter maintained?

2 Cu (s) + O2 (g) 2 CuO (s)

COEFFICIENTS - indicates the number of units of each substance involved.

1. Does the oxygen molecule have a coefficient?

2. What do the subscripts represent?

3. Can subscripts be removed from chemical equations?

How do we Balance Equations?

2 H2 + O2 2 H2O

Subscripts

Coefficients

# of atoms in a compound

Number of compounds in the reaction

Subscripts balance charges within a compound.

Coefficients balance atoms in an equation

What do Coefficients Really Mean?

CH4 + 2 O2 CO2 + 2 H2O

Total:1 C4 H4 O

Total:1 C4 H4 O

The equation is balanced.

H

C

H

HH

O O

O O

CO O HO

H

HO

H

H

CC

H

HH

O O

O O

CCO O HO

H

HO

H

2 C.2-C.3

- Accounting for atoms- Nature’s conservation: Balanced chemical

equations

How to Balance By Inspection:

Taken from Kelly Deters

Make a table of elements

_____ __________

1

Reactants Products

H

O

C

CH4 + O2 H2 O CO2+_____



2 Count the number of each element or ion on the reactants and products side.

_____ __________

Reactants Products

H

O

4

2 3

2

C 1 1

CH4 + O2 H2 O CO2+_____

Don’t forget to add all the atoms of the same element together—even if it appears in more than one compound!



3Each time you add a coefficient, update your table with the new quantities of each atom.

Add coefficients to balance the numbers

_____ __________2

Reactants Products

H

O

4

2 3

2

C 1 1

2

4

44

CH4 + O2 _____ H2 O CO2+



4

Filling each coefficient location lets you and the grader know that you finished the problem rather than you left some blank because you weren’t done!

Place a “1” in any empty coefficient location

_____ __________2

Reactants Products

H

O

4

2 3

2

C 1 1

2

4

44

1 1CH4 + O2 _____ H2 O CO2+

Choosing the Order of Balancing


Save for laterElements that are uncombined

Save for laterElements that appear more than 1 time per side

StartElements that appear

only 1 time per side

StartElements in most

complicated molecules

How do you know what order to balance in?

Pb + PbO2 + H+ Pb2+ + H2O

To balance this equation, use the order: O, H, Pb

How is Balancing Affected by Order?


_____

What happens if we balance in the order determined in the last slide?

Reactants Products

H

Pb

1

2 1

2

O 2 1

4

2

_____ __________1 21 2Pb Pb+ O2 H2 O Pb2++H+_____4+

2

4

O, H, Pb

What about a different order?


2

_____

How is it different if we balance in a different order?

Reactants Products

O

Pb

2

2 1

1

H 1

2

2

_____ __________1 21 2Pb Pb+ O2 H2 O Pb2++H+_____2+

2 4

4

4

You’ll still get to the correct answer, but it will take longer and be more complicated!

H, O, Pb

Let’s Practice #1


Example:Balance the

following equation

__ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O

Let’s Practice #1


Example:Balance the

following equation

__ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O2 1 1 2

HOH

Did you see the “OH” polyatomic ion & change H2O to HOH?

Let’s Practice #2


Example:Balance the

following equation

__ H2 + __ O2 __ H2O

Let’s Practice #2


Example:Balance the

following equation

__ H2 + __ O2 __ H2O2 1 2

Let’s Practice #3


Example:Balance the

following equation

__ Fe + __ O2 ___ Fe2O3

Let’s Practice #3


Example:Balance the

following equation

__ Fe + __ O2 ___ Fe2O34 3 2

C.5 The Mole ConceptDefinition:

Mole – SI unit for counting

Adopted from "Chemistry You Need to Know" by Kelly

Deters

What is a counting unit?


Deters

You’re already familiar with one counting unit…a “dozen”

“Dozen” 12

A dozen doughnuts 12 doughnuts

A dozen books

A dozen cars

A dozen people

12 books

12 cars

12 people

A dozen = 12

How big is a mole? Enough soft drink cans to cover

the surface of the earth to a depth of over 200 miles.

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

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

Adopted from "Chemistry You Need to Know" by

Kelly Deters

A Mole of ParticlesA Mole of Particles Contains 6.02 x 1023

particles1 mole C = 6.02 x 1023 C atoms

1 mole H2O = 6.02 x 1023 H2O molecules

1 mole NaCl= 6.02 x 1023 NaCl “molecules”

Adopted from "Chemistry You Need to Know" by

Kelly Deters

What does a “mole” count in?


Deters

A mole = 6.02 1023 (called Avogadro’s number)

“mole” 6.02 1023

1 mole of doughnuts 6.02 1023 doughnuts

1 mole of atoms

1 mole of molecules

6.02 1023 atoms

6.02 1023 molecules

6.02 1023 = 602,000,000,000,000,000,000,000

C. 6Molar Mass

Adopted from "Chemistry You Need to Know" by Kelly Deters

Definition


Deters

Molar Mass – The mass for one mole of an atom or molecule.

Other terms commonly used for the same meaning:Molecular WeightMolecular MassFormula WeightFormula Mass

Mass for 1 mole of atoms


Deters

The average atomic mass = grams for 1 mole

Element Mass

1 mole of carbon atoms 12.01 g

1 mole of oxygen atoms

1 mole of hydrogen atoms

16.00 g

1.01 g

Unit for molar mass: g/mole or g/mol

Average atomic mass is found on the periodic table

Molar mass for molecules


Deters

The molar mass for a molecule = the sum of the molar masses of all the atoms

Calculating a Molecule’s Mass


Deters

Count the number of each type of atom

Find the molar mass of each atom on the periodic table

Multiple the # of atoms molar mass for each atom

Find the sum of all the masses

1

2

3

4

To find the molar mass of a molecule:

Example: Molar Mass


Deters

Example:Find the

molar mass for

CaBr2

Example: Molar Mass


Deters

Count the number of each type of atom1

Ca

Br

1

2

Example:Find the

molar mass for

CaBr2

Example: Molar Mass


Deters

Find the molar mass of each atom on the periodic table2

Ca

Br

1

2

40.08 g/mole

79.91 g/mole

Example:Find the

molar mass for

CaBr2

Example: Molar Mass


Deters

Multiple the # of atoms molar mass for each atom3

Ca

Br

1

2

40.08 g/mole

79.91 g/mole

Example:Find the

molar mass for

CaBr2

= 40.08 g/mole

= 159.82 g/mole

Example: Molar Mass


Deters

Find the sum of all the masses4

Ca

Br

1

2

40.08 g/mole

79.91 g/mole

= 40.08 g/mole

= 159.82 g/mole+

199.90 g/mole

1 mole of CaBr2 molecules would have a mass of 199.90 g

Example:Find the

molar mass for

CaBr2

Example: Molar Mass & Parenthesis


Deters

Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis.

Example:Find the

molar mass for Sr(NO3)2

Example: Molar Mass & Parenthesis


Deters


1

6

87.62 g/mole

16.00 g/mole

= 87.62 g/mole

= 96.00 g/mole+

211.64 g/mole

1 mole of Sr(NO3)2 molecules would have a mass of 211.64 g

2 14.01 g/mole = 28.02 g/mole

Sr

N

O

Example:Find the

molar mass for Sr(NO3)2

Let’s Practice #2


Deters

Example:Find the

molar mass for Al(OH)3

Let’s Practice #2


Deters


1

3

26.98 g/mole

1.01 g/mole

= 26.98 g/mole

= 3.03 g/mole+

78.01 g/mole

1 mole of Al(OH)3 molecules would have a mass of 78.01 g

3 16.00 g/mole = 48.0 g/mole

Al

O

H

Example:Find the

molar mass for Al(OH)3

C.8Molar Relationships

Equations and Molar Relationships

$1.00 = 4 quarters

If you have 12 quarters than how many $$$’s is that equal to?


Deters

Equations and Molar Relationships

$1.00 = 4 quarters

If you have 12 quarters than how many $$$’s is that equal to?

$3.00

2 H2 + O2 2 H2O

2

No coefficient = 1

2

For every 2 moles of H2…

1 mole of O2 is need to react…

2 moles of H2O are produced

What do those coefficients really mean?

1. What relationships can be found in this equation?

Stoichiometry with MolesExample:

If 4 moles of H2 reacts completely with O2, how many moles of O2 are

needed?2 H2 + O2 2 H2O

Stoichiometry with Moles

4 mole H2

mole H2

mole O2 = ________ mole O2

2

12

From balanced equation: 2 mole H2 1 mole O2

Example:If 4 moles of H2 reacts

completely with O2, how many moles of O2 are

needed?2 H2 + O2 2 H2O

But we can’t measure moles in lab!We can’t go to the lab and count or measure moles…so we need a way to work in measurable units, such as grams and liters!

Molecular mass gives the grams = 1 mole of a compound!

Stoichiometry with Moles & Mass

Example:How many grams of AgCl will be

precipitated if 0.45 mole AgNO3 is reacted as follows:2 AgNO3 + CaCl2 2 AgCl + Ca(NO3)2

From balanced equation: 2 mole AgNO3 2 mole AgCl

Stoichiometry with Moles & Mass

0.45 mole AgNO3

mole AgNO3

mole AgCl = ________ g AgCl

2

265

Molar Mass of AgCl:1 mole AgCl = 143.35 g

mole AgCl

g AgCl

1

143.35

Example:How many grams of AgCl will be

precipitated if 0.45 mole AgNO3 is reacted as follows:2 AgNO3 + CaCl2 2 AgCl + Ca(NO3)2

Stoichiometry with MassExample:

How many grams Ba(OH)2 are precipitated from 14.5 g of NaOH in the

following reaction:2 NaOH + BaCl2 Ba(OH)2 + 2 NaCl

From balanced equation: 2 mole NaOH 1 mole Ba(OH)2

Stoichiometry with Mass

14.5 g NaOH

g NaOH

mole NaOH

= ________ g Ba(OH)2

40.00

1

31.1

Molar Mass of NaOH:1 mole NaCl = 40.00 g

mole NaOH

mole Ba(OH)2

2

1

mole Ba(OH)2

g Ba(OH)2

1

171.35

Molar Mass of Ba(OH)2:1 mole Ba(OH)2 = 171.35 g

Example:How many grams Ba(OH)2 are

precipitated from 14.5 g of NaOH in the following reaction:

2 NaOH + BaCl2 Ba(OH)2 + 2 NaCl

Let’s Practice #1Example:

If you are making 0.57 moles H2O, how many

moles of O2 are needed?2 H2 + O2 2 H2O

Let’s Practice #1

0.57 mole H2O

mole H2O

mole O2 = ________ mole O2

2

10.29

From balanced equation: 2 mole H2O 1 mole O2

Example:If you are making 0.57 moles H2O, how many

moles of O2 are needed?2 H2 + O2 2 H2O

Let’s Practice #2

Example:If you need to precipitate 10.7 g of

Ba(OH)2, how many grams NaOH are needed?


From balanced equation: 2 mole NaOH 1 mole Ba(OH)2

Let’s Practice #2

10.7 g Ba(OH)2

g Ba(OH)2

mole Ba(OH)2

= ________ g NaOH

171.35

1

5.00

Molar Mass of Ba(OH)2:1 mole Ba(OH)2 = 171.35 g

mole Ba(OH)2

mole NaOH

1

2

mole NaOH

g NaOH

1

40.00

Molar Mass of NaOH:1 mole NaCl = 40.00 g

Example:If you need to precipitate 10.7 g of

Ba(OH)2, how many grams NaOH are needed?


Let’s Practice #3

Example:How many moles AgNO3 are needed to

react with 10.7 g CaCl2?2 AgNO3 + CaCl2 2 AgCl + 2 Ca(NO3)2

From balanced equation: 2 mole AgNO3 1 mole CaCl2

Let’s Practice #3

10.7 g CaCl2

g CaCl2

mole CaCl2 = ______ mole AgNO3

110.98

10.193

Molar Mass of CaCl2:1 mole CaCl2 = 110.98 g

mole CaCl2

mole AgNO3

1

2

Example:How many moles AgNO3 are needed to

react with 10.7 g CaCl2?2 AgNO3 + CaCl2 2 AgCl + 2 Ca(NO3)2

C.10 Percent Composition

How many different metals should we use for the coin design?

If using multiple metals, you:

A) Need to know specify how much each material is present

B) Use: Percentage by Mass of each material – Percentage Composition

USA - Penny During 1943 - made of zinc coated steel

After 1943 to 1982 - mostly copper

Since 1982 - made primarily of Zinc

2C.12 Conservation

Depleting Resources Renewable resources Nonrenewable resources Q. If atoms are always conserved, how

can we say that we may be “running out” of a resource?

Conserving Resources Rethinking Reusing Replacing Recycling

Recycling Aluminum

Dealing with Waste

2C.14 The Life Cycle of a Material

Life Cycle of Paper

2.c – conserving matter. 2c.1- keeping track of atoms

Documents

coefficients balance

number of atoms

different order

kelly deterssave

kelly detersexample

kelly detersmake

kelly deters2count

kelly deters4filling