Name:

Date:

Student

Exploration: Stoichiometry

Directions: Follow the

instructions to go through the simulation. Respond to the questions and prompts

in the orange boxes.

Vocabulary: Avogadro’s number, balanced equation, cancel, coefficient, conversion

factor, dimensional analysis, formula mass, molar mass, mole, molecular mass,

stoichiometry

Prior Knowledge Questions (Do these BEFORE

using the Gizmo.)

1.

A 250 mL glass of

orange juice contains 22 grams of sugar. How much sugar is in a two-liter

(2,000 mL)

bottle

of orange juice?

2.

It requires two

sticks of butter to make a batch of 20 cookies. How much butter will it take to

make 150

cookies?

Gizmo Warm-up

Just as a cook

follows a recipe to decide how much of each ingredient to add, a chemist uses stoichiometry to determine the amounts of

substances involved in chemical reactions. The Stoichiometry Gizmo allows you to try your hand at figuring out the

amounts of reactants and products that take part in a chemical reaction.

To begin, check

that this equation is shown:

Fe2O3 + 3CO ? 2Fe + 3CO2

1. Look at the coefficients

(such as the “3” in 3CO) in front of each substance in the equation. The

coefficients tell you how many molecules or atoms take part in a chemical

reaction. In the spaces below, list the number of each molecule or atom in the

equation:

Fe2O3

CO

Fe

CO2

2.

In a balanced equation,

the same number of each kind of atom is shown on each side of the equation.

Calculate the number of iron (Fe), oxygen (O), and carbon atoms (C).

Reactants

Iron:

Oxygen:

Carbon:

Products

Iron:

Oxygen:

Carbon:

Based on these

values, is the equation balanced?

Activity A:

Moles

Get the Gizmo ready:

● Check that the equation is still:

Fe2O3 + 3CO ? 2Fe + 3CO2

● If not, click New equation

until it reappears.

Introduction: A mole is:

A)

A mammal known for digging up gardens.

B)

A small, dark spot on the skin.

C)

A spy embedded within an enemy government.

D)

6.02 × 1023 particles of a substance.

E)

All of the above.

The correct

answer, of course, is E. In chemistry, the mole (mol) is defined as an amount

of a substance that contains 6.022 × 1023 particles of that

substance. This number, called Avogadro’s number,

is special because this number of particles has a mass in grams that is equal

to the mass (in unified mass units) of a single particle of the substance.

Question: How do scientists find the formula mass and molar mass of a

substance?

1.

1. Calculate: The formula mass of a compound is the sum

of the masses of each atom in the chemical formula. The unit of formula mass is

the unified mass unit (u). Formula mass is also called molecular mass if the

compound is composed of molecules.

Iron’s atomic mass is 55.85 u, carbon’s mass is 12.01 u, and oxygen’s

mass is 16.00 u.

A.

Calculate the formula mass of carbon monoxide

(CO) by adding the atomic mass of carbon and

the atomic mass of oxygen:

B.

Calculate the formula mass of carbon dioxide

(CO2):

C.

Calculate the

formula mass of iron (III) oxide (Fe2O3):

2.

Infer: A mole of a substance has a mass in grams that is equal to the formula

mass. For example, a carbon atom has an average mass of 12.01 u. A mole of

carbon has a mass of 12.01 g. Based on their formula masses, list the molar

mass of each substance. The unit for molar mass is g/mol, or grams

per mole.

Fe2O3

CO

Fe

CO2

Check your answers on the Gizmo by inspecting the middle row of tiles on

the right side of the Gizmo. These tiles show the units “1 mol” on top and “g”

below.

3.

Practice: Hydrogen has an atomic mass of 1.01 u. What is the molar mass of these

substances? (Remember to use the units g/mol.)

H2O

CH4

H2CO3

C6H12O6

Activity B:

Canceling units

Get the Gizmo ready:

● Check that the equation is still:

Fe2O3 + 3CO ? 2Fe + 3CO2

Introduction: While solving problems in stoichiometry, it is

useful to pay attention to the units of the answer. The process of comparing

units is called dimensional analysis. A common

technique involves using conversion factors

to convert from one unit to another. Units that appear in the numerator and

denominator of a fraction can be canceled out.

For example, converting 2 moles of carbon monoxide to grams involves

multiplying by a conversion factor:

2 mol CO • 28.01 g CO = 56.02 g CO

1 mol CO

All conversion factors are equivalent to one.

For example, the conversion factor given above is equivalent to one because the

numerator (28.01 g CO) and denominator (1 mol CO) represent the same amount of

CO. The “mol CO” unit is canceled, leaving an answer unit of grams.

Question: How do we solve problems in stoichiometry?

1.

Observe: The first question is: “How many moles of carbon monoxide (CO) are

required to react completely with 1.75 moles of iron (III) oxide (Fe2O3)?”

(If this is not the question you see, click New question until it appears.)

A.

What unit is given in the question?

B.

What quantity is asked for?

2.

Find: Look for the conversion factor that contains the units “mol Fe2O3”

on top and “mol CO” on the bottom. Drag the tile containing this factor down to

the green strip at the bottom.

According

to the tile, how many moles of CO react with one mole of Fe2O3?

3.

Analyze: To get an answer in moles of CO, you need to cancel the moles of Fe2O3.

Turn on Show units.

A.

What

units are given to the right of the equals sign?

B. If these aren’t the units

you want, click Flip tile. What unit

is given now?

4.

Calculate: If the units are correct, multiply or divide the numbers to solve the

problem.

A.

How many moles of CO will react with 1.75

moles of Fe2O3?

B.

Turn on Show

numerical result. Were you correct?

5.

Practice: Turn off Show units and Show numerical result. Click New question, and use what you’ve

learned to solve another stoichiometry problem. For each problem, list the

units given, the units asked for, and the solution.

The problems in

the Gizmo are given in random order, so you may have to click Next question several times to see a

new problem. (Note: Each term in the equation is either a solid (s), liquid

(l), gas (g), or an aqueous solution (aq).)

If you are stuck,

try one of the following hints:

●

If the given unit is grams (or liters or

particles), convert from that unit to moles first. Then convert to moles of the

answer substance.

●

If the answer unit is grams, liters, or

particles, find the number of moles of the answer substance first. Then convert

the moles of answer substance to the desired unit.

●

If you have a calculator, try to calculate the

solution to each problem yourself before turning on the Show numerical solution checkbox.

Problems:

A.

What volume of carbon dioxide (CO2)

will be produced if 2.90 moles of iron (Fe) is produced? [Note: In the Gizmo,

it is assumed that all gases are at standard temperature and pressure, or STP.]

Given

unit:

Answer

unit:

Solution:

B.

What mass of iron (Fe) can be obtained from 3.80

g iron (III) oxide (Fe2O3) reacting with excess carbon

monoxide (CO)?

Given unit:

Answer unit:

Solution:

C.

How many moles of iron (Fe) will be produced

from 6.20 moles of carbon monoxide (CO) reacting with excess iron (III) oxide

(Fe2O3)?

Given unit:

Answer unit:

Solution:

D.

How many molecules of carbon monoxide (CO) are

needed to react with excess iron (III) oxide (Fe2O3) to

produce 11.6 g of iron (Fe)?

Given unit:

Answer unit:

Solution:

6.

On your own: Click New equation to try

solving problems with a new chemical equation. There are five equations in all,

and five problems per equation. The Gizmo will keep track of how many problems

you solve. Good luck!

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