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Session 3.2:

Chemical Reactions

Tom Hsu, PhD.

Manos Chaniotakis, PhD.

Marina Dang, PhD.

Copyright © 2012 Chaniotakas and Hsu

Essential Questions

How do we describe a chemical reaction?

How do we quantify a reaction?

Objectives

• Safely and correctly run three chemical reactions.

• Model each chemical change.

• Use coefficients to balance chemical equations.

Where does the blue “cloud” come from?

TEKS

8 (A) define and use the concept of a mole;8 (B) use the mole concept to calculate the number of atoms, ions, or

molecules in a sample of material;8 (C) calculate percent composition and empirical and molecular

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

equations; and8 (E) perform stoichiometric calculations, including determination of

mass relationships between reactants and products, calculation of limiting reagents, and percent yield.

Assessment

Use 3D models to illustrate and balance the following chemical equation:

How many moles of NaOH does it take to produce 2.7 g of Cu(OH)2?

__ NaOH + __ CuCl2 __ NaCl + __Cu(OH)2

Review

• Chemicals are mixed, but no chemical bonds are broken.

• No new substances are formed.

Physical change Chemical change

• Chemicals bonds are broken and formed. • One or more new substances are

produced.

Water+ food dye

Bleach + food dye

Chemical equations

We use chemical equations to describe chemical reactions.

Chemical equations

Reactants Products

The numbers in front of the chemical formulas are called coefficients.

The general form of a chemical equation is:

Reactant 1 + Reactant 2 Product 1 + Product 2

Safety rules

• Do not consume food or drinks in the lab.

• Wear appropriate protective gear.

• Report all spills and accidents. • Work methodically, and ask

questions if necessary.• Understand the hazards of the

chemicals you are using.Protect yourself against different types of hazards.

Chemical equations

We will now perform, model, and analyze 3 different types of reactions:

1. Acid–base reaction2. Redox (oxidation–reduction) reaction3. Precipitate reaction

Materials

• 5 mL of 1.0 M NaOH

• 5 mL of 1.0 M HCl

• Phenolphthalein

• 1 small piece of Mg

• 1 mL of 1.0 M CuSO4

• 3 test tubes on a rack

• Gloves

• Goggles

1. Add ~2 mL of 1.0 M HCl to a test tube.

2. Add 2 drops of phenolphthalein.

3. Add drops of 1.0 M NaOH until a pink color persists.

4. Write down observations, then safely set chemicals aside.

An acid–base reaction

1. Build models of the reactants HCl and NaOH.

2. Rearrange the atoms from the reactants to build the products NaCl and H2O.

An acid–base reaction

Have students write how many models of HCl and NaOH they started with.

Number of HCl models you built

Number of NaOH models you built

Number of NaCl models you obtained

Number of H2O models you obtained

An acid–base reaction

Have students write how many models of NaCl and H2O they ended up with.

Have students write how many models of HCl and NaOH they started with.

Number of HCl models you built

Number of NaOH models you built

Number of NaCl models you obtained

Number of H2O models you obtained

An acid–base reaction

Have students write how many models of NaCl and H2O they ended up with.

111 1

111 1

2 2Count the number of each type of atom on each side of the reaction arrow.

An acid–base reaction

An acid–base reaction

111 1

2 2

1 1

1 1

1 1

The equation is balanced.

An acid–base reaction

HCl + NaOH NaCl + H2O

How many moles of NaCl is produced if the reaction results in 3.0 mol of H2O?

Chemical equation:

Question:

An acid–base reaction

HCl + NaOH NaCl + H2O

How many moles of NaCl is produced if the reaction results in 3.0 mol of H2O?

Chemical equation:

Question:

Relationship: What is the mole ratio between NaCl and H2O?

An acid–base reaction

HCl + NaOH NaCl + H2O

How many moles of NaCl is produced if the reaction results in 3.0 mol of H2O?

Chemical equation:

Question:

Relationship: What is the mole ratio between NaCl and H2O?

1 mol NaCl

1 mol H2O

An acid–base reaction

HCl + NaOH NaCl + H2O

How many moles of NaCl is produced if the reaction results in 3.0 mol of H2O?

Chemical equation:

Question:

Relationship: What is the mole ratio between NaCl and H2O?

1 mol NaCl

1 mol H2O

Answer: 3.0 mol H2O x = 3.0 mol NaCl

An acid–base reaction

HCl + NaOH NaCl + H2O

How many moles of NaOH does it take to produce 1.8 mol of H2O?

Chemical equation:

Question:

An acid–base reaction

HCl + NaOH NaCl + H2OChemical equation:

Question:

Relationship: What is the mole ratio between NaOH and H2O?

1 mol NaOH

1 mol H2O

How many moles of NaOH does it take to produce 1.8 mol of H2O?

An acid–base reaction

HCl + NaOH NaCl + H2OChemical equation:

Question:

Relationship:

1 mol NaOH

1 mol H2O

Answer: 1.8 mol H2O x = 1.8 mol NaOH

How many moles of NaOH does it take to produce 1.8 mol of H2O?

What is the mole ratio between NaOH and H2O?

1. Add ~3 mL of 1.0 M HCl to a test tube.

2. Carefully add a piece of magnesium.

3. Record your observations.

4. Safely set the chemicals aside.

A redox reaction

1. Build models of the reactants. You may use a 2-hole yellow ball for magnesium.

2. Rearrange the atoms from the reactants to build the products MgCl2 and H2.

A redox reaction

1. Build models of the reactants. You may use a 2-hole yellow ball for magnesium.

2. Rearrange the atoms from the reactants to build the products MgCl2 and H2.

A redox reaction

If you are struggling, try building the products first. Use the atoms from the products to make the reactants.

What do you notice?

Have students write how many models of each chemical they built / obtained.

Number of Mg models you got

Number of HCl models you got

Number of MgCl2 models you used

Number of H2

models you used

A redox reaction

Have students write how many models of each chemical they built / obtained.

Number of Mg models you got

Number of HCl models you got

Number of MgCl2 models you used

Number of H2

models you used

A redox reaction

121 1

Count the number of each type of atom on each side of the reaction arrow.

A redox reaction

121 1

1 1

2 2

2 2

The equation is balanced.

A redox reaction

121 1

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Question: How many moles of Mg does it take to produce 0.45 mol of H2?

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Relationship: What is the mole ratio between Mg and H2?

Question: How many moles of Mg does it take to produce 0.45 mol of H2?

1 mol Mg

1 mol H2

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Relationship: What is the mole ratio between Mg and H2?

Question: How many moles of Mg does it take to produce 0.45 mol of H2?

1 mol Mg

1 mol H2

Answer: 4.5 mol H2 x = 4.5 mol Mg

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Question: How much MgCl2 is produced (in grams) from 1.7 mol of HCl?

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Relationship: What is the mole ratio between MgCl2 and HCl?

1 mol MgCl2

2 mol HCl

Question: How much MgCl2 is produced (in grams) from 1.7 mol of HCl?

A redox reaction

Mg + 2HCl MgCl2 + H2Chemical equation:

Relationship: What is the mole ratio between MgCl2 and HCl?

1 mol MgCl2

2 mol HCl

Question: How much MgCl2 is produced (in grams) from 1.7 mol of HCl?

Answer: 1.7 mol HCl x = 0.85 mol MgCl2

1. Add ~3 mL of 1.0 M NaOH to a test tube.

2. Carefully add 3 to 5 drops of 1.0 M CuSO4.

3. Record your observations.

4. Safely set the chemicals aside.

A precipitate reaction

1. Build models of the reactants. You may model Cu with the orange ball, but remember to only use 2 bonding sites. (Hint: There should be two S=O bonds.)

2. Rearrange the atoms from the reactants to build the products.

A precipitate reaction

If you are struggling, try building the products first. Use the atoms from the products to make the reactants.

A precipitate reaction

1. Build models of the reactants. You may model Cu with the orange ball, but remember to only use 2 bonding sites. (Hint: There should be two S=O bonds.)

2. Rearrange the atoms from the reactants to build the products.

Have students write how many models of each chemical they built / obtained.

Number of NaOH models you got

Number of CuSO4 models you got

Number of Na2SO4 models you used

Number of Cu(OH)2 models you used

A precipitate reaction

Have students write how many models of each chemical they built / obtained.

Number of NaOH models you got

Number of CuSO4 models you got

Number of Na2SO4 models you used

Number of Cu(OH)2 models you used

A precipitate reaction

112 1

Count the number of each type of atom on each side of the reaction arrow.

A precipitate reaction

112 1

The equation is balanced.

A precipitate reaction

2 2

6 6

2 2

1 1

1 1

112 1

2NaOH + CuSO4 Na2SO4 + Cu(OH)2Chemical equation:

Question: How many moles of NaOH does it take to produce 1.4 g of Cu(OH)2?

A precipitate reaction

Chemical equation:

Relationship: What is the mole ratio between NaOH and Cu(OH)2?

2 mol NaOH

1 mol Cu(OH)2

A precipitate reaction

Question: How many moles of NaOH does it take to produce 1.4 g of Cu(OH)2?

2NaOH + CuSO4 Na2SO4 + Cu(OH)2

2 mol NaOH

1 mol Cu(OH)2

Chemical equation:

Relationship:

Answer: 1.4 mol Cu(OH)2 x = 2.8 mol NaOH

A precipitate reaction

2NaOH + CuSO4 Na2SO4 + Cu(OH)2

Question: How many moles of NaOH does it take to produce 1.4 g of Cu(OH)2?

What is the mole ratio between NaOH and Cu(OH)2?

Assessment

• Use 3D models to illustrate and balance the following chemical equation:

• How many moles of NaOH does it take to produce 2.7 g of Cu(OH)2?

__ NaOH + __ CuCl2 __ NaCl + __Cu(OH)2

Assessment

• Use 3D models to illustrate and balance the following chemical equation:

__ NaOH + __ CuCl2 __ NaCl + __Cu(OH)2

Assessment

• Use 3D models to illustrate and balance the following chemical equation:

__ NaOH + __ CuCl2 __ NaCl + __Cu(OH)22 1 12

• How many moles of NaOH does it take to produce 2.7 g of Cu(OH)2?

Assessment

• How many moles of NaOH does it take to produce 2.7 g of Cu(OH)2?

Assessment

Relationship: What is the mole ratio between NaOH and Cu(OH)2?

2 mol NaOH

1 mol Cu(OH)2

• How many moles of NaOH does it take to produce 2.7 g of Cu(OH)2?

Assessment

Relationship: What is the mole ratio between NaOH and Cu(OH)2?

2 mol NaOH

1 mol Cu(OH)2

Answer:2 mol NaOH

1 mol Cu(OH)2

2.7 mol Cu(OH)2 x = 5.4 mol NaOH

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