1 Session 4: Stoichiometry I Tom Hsu, PhD. Manos Chaniotakis, PhD. Marina Dang, PhD. Copyright ©...

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Session 4:

Stoichiometry I

Tom Hsu, PhD.

Manos Chaniotakis, PhD.

Marina Dang, PhD.

Copyright © 2012 Chaniotakas and Hsu

How do we define and measure chemical quantities?– Do we count atoms?– Do we count moles?– Do we measure in grams?– Do we measure in liters?

Essential questions

• Write a balanced chemical equation for a reaction.

• Calculate the number of moles of products and reactants.

• Translate reaction quantities from moles to grams.

• Identify any limiting reactants.

• Apply the concepts to design a stoichiometric reaction to produce a specified quantity of product.

Objectives

8 (A) define and use the concept of a mole;

8 (D) use the law of conservation of mass to write and balance chemical equations; and

8 (E) perform stoichiometric calculations, including determination of mass relationships between reactants and products, calculation of limiting reagents, and percent yield.

TEKS

Consider the above chemical reaction.

1. How many moles of sodium bicarbonate react to form one mole of carbon dioxide?

2. If 1 gram of CO2 is produced, how many grams of sodium bicarbonate were reacted?

3. Calculate the the mass of vinegar needed to completely react with 5 grams of sodium bicarbonate.

Assessment

Setting up the reaction

1. Put an empty cup on the balance and zero it.

Measure 10.0 g of baking soda in the cup. Record the measured mass in Table 1.

2. Put another empty cup on the balance and zero it.

Measure 30.0 g of vinegar in the cup. Record the measured mass in Table 1.

3. Add the masses of vinegar and baking soda. Record the sum in Table 1 (row 3).

Doing the reaction

Slowly pour the vinegar into the baking soda. Pouring it too fast might cause the bubbling to overflow!

Wait until the bubbling has stopped and record the mass.

Observations

a. What evidence did you observe that indicated a chemical reaction was taking place?

b. Explain the difference in the total mass before and after mixing.

c. Do you see any baking soda that has not reacted?

Work out the formula masses

The balanced reaction is written on the first line of the chart above. Calculate the formula mass of each of the products and reactants.

Baking soda (sodium bicarbonate)

Acetic acid(acid in vinegar)

Work out the formula masses

One of the products is a gas. Which one?Will this product’s mass contribute to the mass as measured on the balance after the reaction has finished? Why or why not?

On the second line, write down the mass of the baking soda and vinegar you added.

Baking soda (sodium bicarbonate)

Acetic acid(acid in vinegar)

84.00 60.05 82.03 44.00 18.01

Calculate moles of reactants

Use the formula masses to calculate the number of moles of NaHCO3 and HC2H3O2.

84.00 60.05 82.03 18.0144.00

Vinegar is 5% acetic acid (HC2H3O2) by mass.

Multiply by 0.05 to get the actual mass of acetic acid.

Calculate moles of products

How many moles of CO2 were produced?

Use the formula mass to calculate the mass of CO2 produced.

84.00 60.05 82.03 18.0144.00

Calculate moles of products

Compare the mass of CO2 you calculated with the mass difference you measured from your experiment. Does this explain the “missing” mass?

According to your calculations, did all the baking soda react? Is this consistent with your observations?

What was the limiting reactant in this experiment?

Calculate moles of productsTo make an efficient reaction, there should not be any reactants left over.

Use this chart to calculate how many grams of vinegar need to be added to react completely with 10 grams of baking soda.

84.00 60.05

Test your predictions Measure out 10.0 g of baking soda in one cup.

Measure out the required amount of vinegar (from your calculations) in the other cup.

Write down the total mass before you mix the reactants.

Do the reactionSlowly pour the vinegar into the baking soda. Pouring it too fast might cause the bubbling to overflow!

Wait until the bubbling has stopped and record the mass.

Test your predictions• Calculate the mass of CO2 produced.

• How does this number match your experiment?

84.00 60.05 82.03 44.00 18.01

Chemical manufacturing

• Commodity manufacturers usually take inexpensive raw materials and make a chemical product in a single-purpose factory.

• Gasoline• Polyethylene and other plastics• Cement• Ammonium nitrate fertilizer

• Specialty manufacturers have a general-purpose factory that may produce batches of many different compounds.

• Medical compounds• Dyes• Paints• Foods and food additives

Portland Cement• A hydraulic material which hardens and becomes insoluble when

hydrated.• The main ingredient in concrete, mortar, and stucco.• Manufactured from limestone and clay or shale.

Cement (major components)

• 50% Ca3SiO5

• 25% Ca2SiO4

• 10% Ca3Al2O6

• 10% Ca4Al12Fe2O10

Jubilee Church, Rome

Manufacturingchemistry

Limestone ( CaCO3 )

Shale ( SiO2 + Al2O3 + Fe2O3 )

Cement

• 50% Ca3SiO5

• 25% Ca2SiO4

• 10% Ca3Al2O6

• 10% Ca4Al12Fe2O10

Reactants

Products

Making CO2

• What ingredients do you need to manufacture 10 grams of carbon dioxide using the reaction of sodium bicarbonate and acetic acid?

Making CO2

• What ingredients do you need to manufacture 10 grams of carbon dioxide using the reaction of sodium bicarbonate and acetic acid?

• This is a dumb way to do this, but instructionally useful!

Making CO2

84.00 60.05 82.03 44.00 18.01

Making CO2

84.00 60.05 82.03 44.00 18.01

0.23

Making CO2

84.00 60.05 82.03 44.00 18.01

0.23 0.230.230.230.23

Making CO2

84.00 60.05 82.03 44.00 18.01

0.23 0.230.230.230.23

19.3 g

Making CO2

84.00 60.05 82.03 44.00 18.01

0.23 0.230.230.230.23

19.3 g

13.8 g

276 g

Perfect combustion of octane:

If the fuel is burned perfectly, the reaction that occurs in a gasoline engine would only produce carbon dioxide and water.


a. Calculate the formula mass for octane.

b. Suppose a car uses 25 gallons of gasoline in a week. The density of gasoline is about 2,900 g/gallon. Calculate the mass in grams of 25 gallons of gasoline.


a. Calculate the formula mass for octane. 114.2 g

b. Suppose a car uses 25 gallons of gasoline in a week. The density of gasoline is about 2,900 g/gallon. Calculate the mass in grams of 25 gallons of gasoline.72,500 g


c. Assume gasoline is pure octane. How many moles does this quantity represent?

d. How many moles of CO2 are created for every 2 moles of gasoline burned?

e. Calculate the mass of CO2 released from the perfect combustion of 25 gallons of gasoline.


c. Assume gasoline is pure octane. How many moles does this quantity represent? 635

d. How many moles of CO2 are created for every mole of gasoline burned? 8

e. Calculate the mass of CO2 released from the perfect combustion of 25 gallons of gasoline. 5,080 mol = 223,520 g (223.5 kg)




e. Calculate the mass of CO2 released from the perfect combustion of 25 gallons of gasoline. 5,080 mol = 223,520 g (223.5 kg) from 72.5 kg of gas




e. Calculate the mass of CO2 released from the perfect combustion of 25 gallons of gasoline. 5,080 mol = 114,000 liters = 114 m3 = 30 car volumes

Big ideas

On the atomic level, elements combine by moles, not grams. For example, 2 hydrogen atoms per oxygen atom in H2O.

We cannot measure moles but we can measure grams.

Stoichiometry is the process of converting the quantities in moles from a balanced reaction into measurable quantities in grams.

Assessment


1. How many moles of sodium bicarbonate react to form one mole of carbon dioxide?

Assessment


1. How many moles of sodium bicarbonate react to form one mole of carbon dioxide?One

Assessment


2. If 1 gram of CO2 is produced, how many grams of sodium bicarbonate were reacted?

Assessment


Calculate the the mass of vinegar needed to completely react with 5 grams of sodium bicarbonate.

1 Session 4: Stoichiometry I Tom Hsu, PhD. Manos Chaniotakis, PhD. Marina Dang, PhD. Copyright ©...

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