In this tutorial you will… Determine Atomic and Molecular Weight Define a Mole Convert Between Moles and Grams Calculate Amounts of Reactant and Product

Technical Science

Introduction to Chemistry

Using Chemical Equations

●

In this tutorial you will…

–

Determine Atomic and Molecular Weight

–

Define a Mole

–

Convert Between Moles and Grams

Determine Atomic

and Molecular Weight

●

Any recipe will tell you at least two things:

–

The names of ingredients

–

The amounts of the ingredients

●

When preparing food, the amounts of ingredients

may be measured by mass, weight, or volume

●

But when dealing with a chemical reaction, the

amounts of reactant and product are always

measured by mass.

●

So, lets review how we find the mass of atoms and

molecules.

●

Chemical Equations are simply recipes.

1 of 5

Determine Atomic

and Molecular Weight

2 of 5

●

Find the mass of an atom of Iodine

I

1 atom

=

To find the mass of an atom, simply look up that atom on

the Periodic Table

Periodic Table of the Elements

53 I

Iodine

127.0 Don’t confuse atomic

number with atomic mass. The mass of Iodine is 127.0

127.0

Remember, an atom’s mass is measured in units called AMU’s (atomic mass units)

Determine Atomic

and Molecular Weight

3 of 5

●

Use your Periodic Table to find the atomic masses

of the following atoms in AMU’s

Helium

B

Mg

Cobalt

Sulfur

Sb

Au

Uranium

4.0 AMU

24.5 AMU

32.0 AMU

197.0 AMU

11.0 AMU

59.0 AMU

122.0 AMU

Determine Atomic

and Molecular Weight

4 of 5

●

Find the mass of a molecule of sulfur dioxide.

SO

₂

1 molecule

=

To find the mass of a molecule, first, find the masses of all the atoms in that molecule.

Periodic Table of the Elements

8 O

Oxygen

16.0

16 S

Sulfur

32.0

The mass of one Oxygen = 16.0 The mass of one Sulfur = 32.0

In this molecule there is one atom of Sulfur bonded to

two atoms of Oxygen 1 Sulfur (32 AMU) = 32 2 Oxygen (16 AMU each) = 32

32 + 32 = 64

64

! Remember the Units ! The mass of an atom or molecule is measured in AMU’s

AMU’s

16.0

Determine Atomic

and Molecular Weight

5 of 5

●

Use your Periodic Table to find the masses of the

following molecules.

Home

N

HNO

Water

Mg(OH)

SbCl

Potassium

Chloride

ZnSO

C

H

O

28.0 AMU

H

2O

18 AMU

228.5 AMU

161.5 AMU

63.0 AMU

58.5 AMU

KCl 74.5 AMU

Define a Mole

1 of 10

Home

●

What does the balanced equation below tell you?

2 NH

₃

N

₂

+ 3 H

₂

●

This equation tells us that 2 molecules of ammonia

(NH

) react to produce 1 molecule of nitrogen gas

and 3 molecules of hydrogen gas.

●

With this information, you could determine the

amount of any reactant or product so long as you

know the amount of one of the ingredients.

Define a Mole

2 of 10

●

If 4 molecules of ammonia react how many

molecules of N

and H

will be produced?

2 NH

₃

N

₂

+ 3 H

₂

First, write down the amount of the reactant or product that you are given.

4 molecules of NH₃ in this case. 4 molecules NH₃

Use the information from the balanced equation to determine the relationship between the given

substance and the unknown substance. Let’s find the amount of N₂ first.

The relationship between NH₃ and N₂ is 2 to 1. Two molecules of NH₃ produces one molecule of N₂.

We will use this ratio ( 2 NH₃ to 1 N₂ ) as a conversion factor to convert from

an amount of ammonia to an amount of nitrogen.

x

2 molecules NH₃ 1 molecule N₂

Perform the calculation: 4 ÷ 2 = 2

Two NH₃ molecules produce one N₂ molecule. So, four NH₃ molecules produces two N₂ molecules.

2 molecules N₂

=

Calculate the number of molecules of H₂ produced. Again, start your calculation with the

given information: 4 molecules of NH₃ 4 molecules NH₃

What’s the relationship between NH₃ and H₂? The equation tells us that 2 ammonia molecules

will produce 3 hydrogen molecules. Use that ratio as a conversion factor.

2 NH₃ to 3 H₂

x

2 molecules NH₃ 3 molecules H

2

Perform the calculation: 4 x 3 ÷ 2 = 6

Two NH₃ molecules produces three H₂ molecules. So, four NH₃ molecules produces six H₂ molecules.

6 molecules H₂

=

The coefficients provided by the balanced chemical equation can be used as conversion factors to convert

Define a Mole

3 of 10

●

If 8 molecules of MnCl

were produced, how

many molecules of HCl and MnO

reacted?

MnO

+ 4 HCl MnCl

+ Cl

+ 2 H

O

8 molecules MnCl

2

x

1 molecule MnCl₂ 4 molecules HCl

32 molecules HCl

=

8 molecules MnCl₂

x

1 molecule MnCl₂ 1 molecule MnO

2 _{8 molecules MnO} 2

Define a Mole

4 of 10

●

The coefficients in a balanced chemical reaction

can be used as conversion factors.

●

They can determine the number of molecules of

any reactant or product if you are given a number

of molecules of one other substance.

●

To determine a number of atoms or molecules is

good information but it really isn’t very practical.

●

It would be nearly impossible to measure out

substances an atom or a molecule at a time.

Define a Mole

5 of 10

●

Take another look at the following equation.

2 Na + Cl

₂

2 NaCl

●

We have a recipe for making 2 molecules of

sodium chloride.

●

But what if we wanted more than two molecules of

sodium chloride? Would we need another recipe?

●

No, like any recipe, if you want more product you

increase the amounts of the ingredients.

Define a Mole

6 of 10

●

This equation can be read in a number of ways.

2 Na + Cl

₂

2 NaCl

2 atoms of Na react with

1 molecule of Cl

to produce

2 molecules of NaCl

But since it is nearly impossible to measure out

a single atom or molecule,

the equation could also be read this way.

200 atoms of Na react with

100 molecules of Cl

to produce

200 molecules of NaCl

It could be read this way.

2 million atoms of Na react with

1 million molecules of Cl

to produce

2 million molecules of NaCl

We will continue to scale up our recipe

until we get enough atoms or molecules

that we can conveniently measure.

As it turns out, the most convenient

number to work with

is 6.02 x 10

atoms or molecules.

6.02 x 10

is a very large number.

602,000,000,000,000,000,000,000

Why does it have to be so large?

Atoms and molecules are very small

and it takes a lot of them to make

a significant amount of matter.

In fact it would take about 20 million atoms

lined up end to end to cross the period

at the end of this sentence.

6.02 x 10

is enough atoms or molecules to

actually see, touch, and measure.

Since 6.02 x 10

is so large,

chemists have given this number a name.

6.02 x 10

is called one Mole.

Just like 12 is one Dozen,

and 144 is one Gross,

6.02 x 10

is one Mole.

So, our chemical equation

could also be read

in terms of moles.

2 moles of Na atoms react with

1 mole of Cl

molecules to produce

Define a Mole

7 of 10

●

Define a mole

Α

A mole is a convenient number of atoms or

molecules with which to work.

One mole is 6.02 x 10

particles.

Define a Mole

8 of 10

●

If 5 moles of ammonia react how many moles

of N

and H

will be produced?

2 NH

₃

N

₂

+ 3 H

₂

First, write down the amount of the reactant or product that you are given.

5 moles of NH₃ in this case. 5 moles NH₃

Use the information from the balanced equation to determine the relationship between the given

substance and the unknown substance. Let’s find the amount of N₂ first.

The relationship between NH₃ and N₂ is 2 to 1. Two moles of NH₃ produces one mole of N₂.

We will use this ratio ( 2 NH₃ to 1 N₂ ) as a conversion factor to convert from

an amount of ammonia to an amount of nitrogen.

x

2 moles NH₃ 1 mole N₂

Perform the calculation: 5 ÷ 2 = 2.5

Two moles of NH₃ produce one mole of N₂. So, five moles of NH₃ produces 2.5 moles of N₂.

2.5 moles N₂

=

5 moles NH₃

x

2 moles NH₃ 3 moles H

2 7.5 moles H

2

=

It’s okay to have a part of a mole of a substance. Like a dozen, a mole is just a number. You can have

a 2.5 dozen so you can have 2.5 moles.

Calculate the number of moles of H₂ produced. Again, start your calculation with the

given information: 5 moles of NH₃

What’s the relationship between NH₃ and H₂? The equation tells us that 2 moles of ammonia will

produce 3 moles of hydrogen. Use that ratio as a conversion factor.

2 NH₃ to 3 H₂

Perform the calculation: 5 x 3 ÷ 2 = 7.5 Two moles of NH₃ produces three moles of H₂. So, five moles of NH₃ produces 7.5 moles of H₂. The coefficients provided by the balanced chemical equation can be used as conversion factors to convert

Define a Mole

9 of 10

●

If 0.5 moles of MnCl

were produced, how many

moles of HCl and MnO

reacted?

MnO

+ 4 HCl MnCl

+ Cl

+ 2 H

O

0.5 moles MnCl

2

x

1 mole MnCl₂ 4 moles HCl

2 moles HCl

=

0.5 moles MnCl₂

x

1 mole MnCl₂ 1 mole MnO

2 _{0.5 moles MnO} 2

Define a Mole

10 of 10

●

In this section, you found that a chemical equation

can be interpreted in terms of atoms & molecules

or in terms of moles.

●

You discovered that a mole (6.02 x 10

) particles

is a convenient number of atoms or molecules

●

You also calculated the amounts of reactants and

products in terms of atoms and molecules and in

terms of moles.

●

However, even with what we know now, our

chemical equation still isn’t very practical.

●

The next section will show how to make a

chemical equation functional.

Convert Between

Moles and Grams

1 of 10

●

Read the following equation in terms of moles.

Home

4 Al + 3 O

₂

2 Al

₂

O

₃

4 moles of Al atoms react with

3 moles of O

molecules to produce

2 moles of Al

O

molecules.

Once again, this is good information because it shows the ratio of the amounts of reactants and products.

We also know that a mole of a substance is convenient to work with because it represents

enough particles to actually measure. However, there is still a problem.

Let’s say we want to produce 2 moles of Al₂O_3. We would need 4 moles of Aluminum (Al). How would you measure 4 moles of aluminum? Would you count out the aluminum atoms one at

a time until you got to 4 moles? Of course not.

Atoms are too small to count individually and it would take forever to count to 4 moles.

So what would you do?

If a mole is a convenient amount of particles, there must be a convenient way

to measure a mole of atoms or molecules. The rest of this section will show you how to

measure a mole of atoms or molecules. This is going to make chemical equations

2 of 10

●

The primary means of measuring amounts of

substances in a chemistry lab is by mass.

●

In the first section, we found masses of atoms and

molecules by reading the Periodic Table.

●

Now we will determine the mass of a mole of

atoms or molecules.

●

This really isn’t as difficult as it may sound

3 of 10

Convert Between

Moles and Grams

●

Find the mass of one atom of hydrogen and the

mass of one mole of hydrogen atoms.

1 Atom of Hydrogen

=

Mass of 1 Atom of Hydrogen

To find the mass of a single atom, simply look up the mass of that atom on the Periodic Table.

Hydrogen has a mass of 1.0 AMU

1.0 AMU

1 mole of Hydrogen Atoms

Now let’s find the mass of one mole of hydrogen atoms.

Remember:

A mole is 6.02 x 1023 particles.

602,000,000,000,000,000,000,000 atoms

=

Mass of 1 Mole of Hydrogen Atoms

6.02 x 1023 atoms

If one atom of hydrogen has a mass of 1 AMU, then 1 mole of hydrogen atoms must have a

mass of 6.02 x 1023 AMU’s

6.02 x 10

AMU’s

You’re probably saying this doesn’t look very easy or convenient. However, there is a

relationship that simplifies the process. 6.02 x 1023 AMU’s is equal to 1.0 gram.

1.0 Gram

So, the mass of 1 atom of H is 1.0 AMU. The mass of 1 mole of H atoms is 1.0 gram.

Notice the number (1.0) is the same.

This simplifies the process a great deal because that number was very easy to find.

We just read it off the Periodic Table.

This relationship holds true for any atom or molecule. If one molecule of water has a mass of 18 AMU’s, then

one mole of water molecules has a mass of 18 grams. Note: Don’t get the idea that 1 AMU is equal to 1 gram

4 of 10

Convert Between

Moles and Grams

●

Determine the mass of 1 mole of the following

atoms and molecules.

Atom

Mass

(1 mole)

Molecule

Mass

(1 mole)

Be

CH

Iron

N

Ba

Ca(NO

)

Gold

H

CO

9.0 grams

56.0 grams

137.5 grams

197.0 grams

16.0 grams

28.0 grams

164.0 grams

62.0 grams

The mass of one mole of a substance is such an important relationship it is given its own name.

The mass of one mole of atoms is called the Gram Atomic Weight

The mass of one mole of molecules is called the Gram Molecular Weight

The Gram Atomic Weight of iron is 56.0 grams / 1 mole

Convert Between

Moles and Grams

5 of 10

●

How much Al would be required to produce

2 moles of Al

O

?

4 Al + 3 O

₂

2 Al

₂

O

₃

From the information given in the balanced chemical equation, you know that it would take

4 moles of Al to produce 2 moles of Al₂O₃.

4 moles Al

It is important to know we need 4 moles of Al. But that information isn’t very practical.

We want to know the amount in grams. We need to know the amount

in grams rather than moles

because we measure substances by mass. We can convert from moles to grams by using

the Gram Atomic Weight of Al. 27.0 grams / 1 mole of Al The Gram Atomic Weight of Al

27.0 grams / 1 mole of Al

will be used as a conversion factor.

x

1 mole Al

27.0 grams

Perform the calculation: 4 x 27.0 = 108 4 moles of Al = 108 grams

= 108 grams

The Gram Atomic Weight allows us to determine amounts of reactants and products in terms of

grams rather than moles.

That’s important because, if we were to actually perform this reaction in the lab, the reactants

6 of 10

Convert Between

Moles and Grams

●

Calculate mass in grams of the given number of

moles of the following substances.

5 moles Na

1.5 moles O

0.75 moles H

O

3 moles NaOH

x

1 mole Na

23 grams

= 115 grams of Na

x

1 mole O

32 grams

= 48 grams of O

x

1 mole H

O

18 grams

= 13.5 grams of H

O

x

1 mole NaOH

40 grams

Convert Between

Moles and Grams

7 of 10

●

We determined the Gram Atomic Weight and the

Gram Molecular Weight for atoms and molecules.

●

We also used the Gram Molecular Weight (GMW)

and the Gram Atomic Weight (GAW) as a

conversion factor.

●

This allowed us to calculate the amount in grams

of a substance when given the number of moles.

●

We can also use the Gram Molecular Weight

(or the GAW) to convert from grams of a

8 of 10

Convert Between

Moles and Grams

●

153 grams of Al

O

is how many moles.

Just like any conversion, the first step is to write down the measurement

you are trying to convert.

Next, we need a conversion factor.

The Gram Molecular Weight is the conversion factor because it relates mass to moles.

153 g Al

2

O

GMW of Al₂O₃ = 102 grams / 1 mole Al 2 x 27 = 54

O 3 x 16 = 48 54 + 48 = 102

The GMW of Al₂O₃ is 102 grams / mole We want to convert from grams to moles. So, grams must cancel which means 102 grams

will be on the bottom of the conversion factor.

x

102 grams

1 mole Al

O

Perform the calculation: 153 ÷ 102 = 1.5

153 grams of Al₂O₃ is 1.5 moles

9 of 10

Convert Between

Moles and Grams

●

Calculate number of moles of the following

substances given the mass in grams.

3 grams C

142 grams Cl

595 g AgNO

234 g Mg(OH)

x

12 grams

1 mole C

= 0.25 moles of C

x

71 grams

1 mole Cl

= 2 moles of Cl

x

170 grams

1 mole AgNO

= 3.5 moles of AgNO

x

58.5 grams

1 mole Mg(OH)

_{= 4 moles of}

10 of 10

Convert Between

Moles and Grams

●

In this section we determined Gram Atomic

Weights and Gram Molecular Weights of atoms and

molecules

●

We used the Gram Molecular Weight (GMW) and

the Gram Atomic Weight (GAW) as conversion

factors.

●

This allowed us to convert from moles to grams

and from grams to moles

●

In the next section we put all this information

together to solve some practical problems in

chemistry.

Calculate Amounts of

Reactant and Product

1 of 5

●

Chemical equations are essential to any industry

that produces or uses chemicals.

Home

●

A company doesn’t want to use more of a reactant

than is necessary or produce extra product that

could end up as waste.

●

Chemical equation can be used to determine exact

amounts of reactants and products.

●

All we need is a balanced chemical equation and

the amount in grams of one reactant or product.

?

2 moles Fe

112 g

2 of 5

Calculate Amounts of

Reactant and Product

●

How many g of C is needed to produce 112 g of Fe.

2 Fe

₂

O

₃

+ 3 C 4 Fe + 3 CO

₂

Solving this problem involves three steps. The good news is that we have already done each of these steps independently.

Now, we will put them all together. Identify the given information and the information you are supposed to find.

Given = 112 g Fe Find = ? g C

Step 1: Convert grams of the given substance (Fe) to moles. Use the Gram Atomic Weight as the conversion factor.

GAW of Fe = 56.0 grams / mole

112 g Fe _x

56 grams 1 mole Fe

= 2 moles Fe

Step 2: Convert moles of iron to moles of carbon. Use the ratio from the balanced chemical equation.

3 moles of C react to form 4 moles of Fe. x

4 moles Fe 3 moles C

= 1.5 moles C

Step 3: Convert moles of the desired substance (C) to grams. Use the Gram Atomic Weight as the conversion factor.

GAW of C = 12.0 grams / mole

1.5 moles C _x

1 mole C 12 grams

= 18 grams C

112 g of iron is 2 moles. The ratio of Cto Fe is 3 to 4, so 1.5 moles of C is needed to produce 2 moles of Fe.

1.5 moles of C is 18 grams.

18 g

On the next slide,

Calculate Amounts of

Reactant and Product

3 of 5

●

How much (g) Fe

O

is needed to make 112 g of Fe

2 Fe

₂

O

₃

+ 3 C 4 Fe + 3 CO

₂

112 g 18 g

Step 1: Convert grams of the given substance (Fe) to moles. Use the Gram Atomic Weight as a conversion factor.

Fe = 56 grams / 1 mole

112 g Fe _x

56 grams 1 mole Fe

= 2 moles Fe

We already did this calculation when we solved the first problem so we could have started this problem with Step 2.

However, we did the calculation again for practice. Step 2: Convert moles of Fe to moles of Fe₂O₃. Use the ratio from the balanced chemical equation.

2 moles of Fe₂O₃ react to produce 4 moles of Fe

2 moles Fe _x

4 moles Fe 2 moles Fe

2O3 _{= 1 mole Fe} 2O3

Step 3: Convert moles of Fe₂O₃ to grams of Fe₂O₃. Use the Gram Molecular Weight as a conversion factor.

GMW of Fe₂O₃ = 160 grams / 1 mole

1 mole Fe

2O3 x

1 mole Fe

2O3

160 grams

= 160 grams Fe₂O₃

112 g of iron is 2 moles. The ratio of Fe₂O₃ to Fe is 2 to 4, so 1 mole of Fe₂O₃ is needed to produce 2 moles of Fe.

1 mole of Fe₂O₃ is 160 grams.

160 g

On the next slide,

4 of 5

Calculate Amounts of

Reactant and Product

●

How much (g) CO

is needed to make 112 g of Fe

2 Fe

₂

O

₃

+ 3 C 4 Fe + 3 CO

₂

112 g 18 g

160 g

Step 1: Convert grams of the given substance (Fe) to moles. Use the Gram Atomic Weight as a conversion factor.

Fe = 56 grams / 1 mole

112 g Fe _x

56 grams 1 mole Fe

= 2 moles Fe

We already did this calculation when we solved the first problem so we could have started this problem with Step 2.

However, we did the calculation again for practice. Step 2: Convert moles of Fe to moles of CO₂. Use the ratio from the balanced chemical equation. 4 moles of Fe are produced along with 3 moles of CO₂

2 moles Fe _x

4 moles Fe 3 moles CO

2 _{= 1.5 moles CO} 2

Step 3: Convert moles of CO₂ to grams of CO₂.

Use the Gram Molecular Weight as a conversion factor. GMW of CO₂ = 44 grams / 1 mole

1.5 moles CO

2 x

1 mole CO

2

44 grams

= 66 grams CO₂

112 g of iron is 2 moles. The ratio of CO₂ to Fe is 3 to 4, so 1.5 moles of CO₂ is produced along with 2 moles of Fe.

1.5 moles of CO₂ is 66 grams.

We have now calculated the amounts of each reactant and product in this equation starting from a single given amount.

Best of all we used a practical unit of measure (grams).

66 g

There is one more thing you should notice. Look at the total amount of the reactants compared to the total amount of the products.

Reactants 160 g + 18 g = 178 grams Products 112 g + 66 g = 178 grams

The total mass of reactants equals the total mass of products. This is confirmation of the Law of Conservation of Matter. Matter can’t be created or destroyed only changed in form.

Explore Common

Chemical Reactions

5 of 5

●

Explain how you would convert from grams of a

substance to moles or vice versa?

Α

The Gram Molecular Weight or the Gram Atomic

Weight can be used a conversion factor to convert

from grams to moles or moles to grams.

●

How would you convert from moles of one

substance to moles of another substance?

Α

To convert from an amount of one substance to an

amount of another substance requires a balanced

chemical equation. The coefficients on the

substances will be used as the conversion factor.

Technical Science

Introduction to Chemistry

You have Completed

Using Chemical Equations