Session 3.2:
Chemical Reactions
Tom Hsu, PhD.
Manos Chaniotakis, PhD.
Marina Dang, PhD.
Copyright © 2012 Chaniotakas and Hsu
1
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; and
8 (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:
__ NaOH + __ CuCl2  __ NaCl + __Cu(OH)2
How many moles of NaOH does it take to produce
2.7 g of Cu(OH)2?
Review
Physical change
Chemical change
• Chemicals are mixed, but no
chemical bonds are broken.
• No new substances are formed.
• 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
The general form of a chemical equation is:
Reactant 1 + Reactant 2
Reactants
Product 1 + Product 2
Products
The numbers in front of the chemical formulas are called coefficients.
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
Materials
• 5 mL of 1.0 M NaOH
We will now perform, model, and
analyze 3 different types of reactions:
• 5 mL of 1.0 M HCl
• Phenolphthalein
• 1 small piece of Mg
1. Acid–base reaction
2. Redox (oxidation–reduction) reaction
3. Precipitate reaction
• 1 mL of 1.0 M CuSO4
• 3 test tubes on a rack
• Gloves
• Goggles
An acid–base reaction
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
Have students write how many models
of NaCl and H2O they ended up with.
Number of NaCl
models you obtained
Number of H2O
models you obtained
An acid–base reaction
Have students write how many models
of HCl and NaOH they started with.
1
Number of HCl
models you built
1
Number of NaOH
models you built
Have students write how many models
of NaCl and H2O they ended up with.
1
Number of NaCl
models you obtained
1
Number of H2O
models you obtained
An acid–base reaction
1
Count the number of
each type of atom on
each side of the
reaction arrow.
1
1
1
2
2
An acid–base reaction
1
The equation is
balanced.
1
1
1
2
1
2
1
1
1
1
1
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaCl is produced if the reaction
results in 3.0 mol of H2O?
NaCl + H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaCl is produced if the reaction
results in 3.0 mol of H2O?
Relationship:
What is the mole ratio
between NaCl and H2O?
NaCl + H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaCl is produced if the reaction
results in 3.0 mol of H2O?
Relationship:
What is the mole ratio
between NaCl and H2O?
NaCl + H2O
1 mol NaCl
1 mol H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaCl is produced if the reaction
results in 3.0 mol of H2O?
Relationship:
What is the mole ratio
between NaCl and H2O?
Answer:
NaCl + H2O
1 mol NaCl
3.0 mol H2O x
= 3.0 mol NaCl
1 mol H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaOH does it take to produce 1.8 mol
of H2O?
NaCl + H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaOH does it take to produce 1.8 mol
of H2O?
Relationship:
What is the mole ratio
between NaOH and H2O?
NaCl + H2O
1 mol NaOH
1 mol H2O
An acid–base reaction
Chemical
equation:
HCl + NaOH
Question:
How many moles of NaOH does it take to produce 1.8 mol
of H2O?
Relationship:
What is the mole ratio
between NaOH and H2O?
Answer:
NaCl + H2O
1 mol NaOH
1.8 mol H2O x
= 1.8 mol NaOH
1 mol H2O
A redox reaction
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.
If you are struggling, try building the products first.
Use the atoms from the products to make the reactants.
What do you notice?
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
Have students write how many models of each chemical they built / obtained.
1
Number of Mg
models you got
2
Number of HCl
models you got
1
Number of MgCl2
models you used
1
Number of H2
models you used
A redox reaction
1
Count the number of
each type of atom on
each side of the
reaction arrow.
2
1
1
A redox reaction
1
The equation is
balanced.
2
1
1
1
2
1
2
2
2
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How many moles of Mg does it take to produce 0.45 mol
of H2?
MgCl2 + H2
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How many moles of Mg does it take to produce 0.45 mol
of H2?
Relationship:
What is the mole ratio
between Mg and H2?
MgCl2 + H2
1 mol Mg
1 mol H2
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How many moles of Mg does it take to produce 0.45 mol
of H2?
Relationship:
What is the mole ratio
between Mg and H2?
Answer:
MgCl2 + H2
1 mol Mg
4.5 mol H2 x
= 4.5 mol Mg
1 mol H2
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How much MgCl2 is produced (in grams) from 1.7 mol of HCl?
MgCl2 + H2
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How much MgCl2 is produced (in grams) from 1.7 mol of HCl?
Relationship:
What is the mole ratio
between MgCl2 and HCl?
MgCl2 + H2
1 mol MgCl2
2 mol HCl
A redox reaction
Chemical
equation:
Mg + 2HCl
Question:
How much MgCl2 is produced (in grams) from 1.7 mol of HCl?
Relationship:
What is the mole ratio
between MgCl2 and HCl?
Answer:
MgCl2 + H2
1 mol MgCl2
1.7 mol HCl x
= 0.85 mol MgCl2
2 mol HCl
A precipitate reaction
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
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.
If you are struggling, try building the products first.
Use the atoms from the products to make the reactants.
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
Have students write how many models of each chemical they built / obtained.
2
Number of NaOH
models you got
1
Number of CuSO4
models you got
1
Number of Na2SO4
models you used
1
Number of Cu(OH)2
models you used
A precipitate reaction
2
Count the number of
each type of atom on
each side of the
reaction arrow.
1
1
1
A precipitate reaction
2
The equation is
balanced.
1
1
1
2
2
6
6
2
2
1
1
1
1
A precipitate reaction
Chemical
equation:
2NaOH + CuSO4
Question:
How many moles of NaOH does it take to produce 1.4 g of
Cu(OH)2?
Na2SO4 + Cu(OH)2
A precipitate reaction
Chemical
equation:
2NaOH + CuSO4
Question:
How many moles of NaOH does it take to produce 1.4 g of
Cu(OH)2?
Relationship:
What is the mole ratio between
NaOH and Cu(OH)2?
Na2SO4 + Cu(OH)2
2 mol NaOH
1 mol Cu(OH)2
A precipitate reaction
Chemical
equation:
2NaOH + CuSO4
Question:
How many moles of NaOH does it take to produce 1.4 g of
Cu(OH)2?
Relationship:
What is the mole ratio between
NaOH and Cu(OH)2?
Answer:
Na2SO4 + Cu(OH)2
2 mol NaOH
1.4 mol Cu(OH)2 x
= 2.8 mol NaOH
1 mol Cu(OH)2
Assessment
• Use 3D models to illustrate and balance the following
chemical equation:
__ NaOH + __ CuCl2  __ NaCl + __Cu(OH)2
• How many moles of NaOH does it take to produce 2.7 g
of 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:
2 NaOH + __
1 CuCl2  __
2 NaCl + __Cu(OH)
1
__
2
Assessment
• 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?
Relationship:
What is the mole ratio between
NaOH and Cu(OH)2?
2 mol NaOH
1 mol Cu(OH)2
Assessment
• How many moles of NaOH does it take to produce 2.7 g
of Cu(OH)2?
Relationship:
What is the mole ratio between
NaOH and Cu(OH)2?
2 mol NaOH
1 mol Cu(OH)2
Answer:
2 mol NaOH
2.7 mol Cu(OH)2 x
= 5.4 mol NaOH
1 mol Cu(OH)2
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