Transcript Document

Living By Chemistry
Unit 4: TOXINS
Stoichiometry, Solution Chemistry, and Acids and Bases
In this unit you will learn:
• how toxins are defined
• how chemists determine toxicity
• the mechanisms by which toxic
substances act in our bodies and what
this has to do with chemical reactions
Section I: Toxic Changes
Lesson 1 Toxic Reactions
Lesson 2 Making Predictions
Lesson 3 Spare Change
Lesson 4 Some Things Never Change
Lesson 5 Atom Inventory
Lesson 6 What’s Your Reaction?
Lesson 1: Toxic Reactions
Chemical Equations
Day 1 ChemCatalyst
1. What toxins have you encountered in your
life?
2. How can toxins enter the body?
3. How can toxins harm you?
Key Question
How do chemists keep track of changes in matter?
You will be able to:
• complete basic translations of chemical
equations
• give a basic definition of a toxin
Prepare for the Demonstration
Work in pairs.
Prepare for the Demonstration
(cont.)
Hydrochloric acid is corrosive. Wear safety
goggles. Have extra baking soda on hand for spills.
HCl(aq) + NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g)
Discussion Notes
HCl(aq) + NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g)
The chemical equation represents a change in
matter using symbols and formulas.
Discussion Notes (cont.)
Toxins can enter the body in a limited number of
ways.
Toxins often react with water in the human body.
Toxins may be molecular, ionic, or metallic
substances.
Wrap Up
How do chemists keep track of changes in matter?
• Chemical equations help chemists keep track of
the substances involved in chemical changes.
• Chemical equations use chemical formulas to
indicate the reactants and products of chemical
changes. They also show what phase a
compound is in.
• Toxins are substances that interact with living
organisms and cause harm.
Check-in
Consider this reaction between sodium cyanide
and a solution of hydrochloric acid:
NaCN(s)  HCl(aq)  NaCl(aq)  HCN(g)
a. Write an interpretation of the chemical
equation.
b. Sodium cyanide is highly toxic. What is the
most likely way it will enter the body?
Lesson 2: Making Predictions
Observing Change
Day 2 ChemCatalyst
Consider this chemical equation:
AgNO3(aq)  KCl(aq)  KNO3(aq)  AgCl(s)
a) What do you expect to observe if you carry out
this reaction in a laboratory?
b) Write an interpretation of the chemical equation,
describing what is taking place.
Key Question
How can you predict what you will observe based
on a chemical equation?
You will be able to:
• relate chemical equations to real-world
observations
• make predictions based on chemical equations
Discussion Notes
AgNO3(aq)  KCl(aq)  KNO3(aq)  AgCl(s)
Discussion Notes (cont.)
Chemical equations contain certain information
that you can use to predict what you might observe
if a procedure is performed.
Sometimes change is described by more than one
chemical equation.
Chemical equations allow you to track changes in
matter on an atomic level.
There is some information that a chemical
equation can’t provide.
Wrap Up
How can you predict what you will observe based on
a chemical equation?
• Chemical equations allow chemists to predict
and track changes in matter. They indicate how
many products are formed, what those products
are, and the phase of each product.
• Observations of chemical procedures provide
information not covered by a chemical equation
(and vice versa). Observations alone cannot tell
you what substances are present.
Check-in
Examine this chemical equation. Write an
interpretation of the chemical equation, describing
what is taking place.
CaCl2(aq) + 2NaOH(aq)  Ca(OH)2(s)  2NaCl(aq)
Lesson 3: Spare Change
Physical Versus Chemical Change
Key Question
How are changes in matter classified?
Day 3 ChemCatalyst
Does this chemical equation describe a physical
change or a chemical change?
Explain how you can tell.
C17H17O3N(s) + 2C4H6O3(l)  C21H21O5N(s) + 2C2H4O2(l)
You will be able to:
• define physical and chemical change and
explain the gray areas between them
• classify chemical equations as representing
physical changes or chemical changes
Discussion Notes
Physical changes are changes in the appearance
or form of a substance.
Chemical changes produce new substances with
new properties.
Physical change: A change in matter in which a
substance changes form but not identity.
Chemical change: A change in matter that results
in the formation of a new substance or substances
with new properties.
Discussion Notes (cont.)
CoCl2(s)  CoCl2(aq)
CoCl2(aq) + Ca(OH)2(aq)  Co(OH)2(s) + CaCl2(aq)
It is not always possible to distinguish between
physical and chemical change based on
observations alone.
It is possible to argue that dissolving a substance in
water changes the properties of that substance.
Discussion Notes (cont.)
Ionic compounds do not dissolve in the same way
as molecular solids.
The dissolving of ionic solids can be shown with a
type of equation that stresses the formation of ions
in solution.
CaCl2(s)  CaCl2(aq)
CaCl2(s)  Ca2(aq) + 2Cl−(aq)
Wrap Up
How are changes in matter classified?
• Chemical changes involve the formation of new
substances.
• Physical changes, such as phase changes,
involve a change in form.
• Dissolving generally is considered a physical
change, but it has something in common with
chemical change as well.
• Chemical equations often provide more
straightforward information about the type of
change than do mere observations.
Lesson 4: Some Things Never Change
Conservation of Mass
Key Question
How does mass change during a chemical or
physical change?
Lesson 5: Atom Inventory
Balancing Chemical Equations
Key Question
How do you balance atoms in a chemical equation?
Day 4 ChemCatalyst
Consider this reaction:
Na2CO3(aq) + CaCl2(aq)  2NaCl(aq) +
CaCO3(s)
a. Describe what you will observe when sodium
carbonate, Na2CO3(aq), and calcium chloride,
CaCl2(aq), are mixed.
b. Will the mass increase, decrease, or stay the
same after mixing? Explain.
c. Does this reaction obey the law of
conservation of mass? Why or why not?
Wrap Up
How does mass change during a chemical or
physical change?
• Individual atoms are conserved in chemical
reactions and physical changes: The number of
atoms of each element remains the same from
start to finish.
• Mass is conserved in chemical reactions: The
total mass of the products equals the total mass
of the reactants.
Wrap Up (cont.)
• The law of conservation of mass states that
matter can be neither created nor destroyed in
physical and chemical changes. Matter is
conserved.
• Gases have mass.
Check-in
Consider this reaction:
CuCO3(s) + H2SO4(aq)  CO2(g) + CuSO4(aq) +
H2O(l)
a. Describe what you will observe when copper (II)
carbonate, CuCO3(s), and sulfuric acid,
H2SO4(aq), are mixed.
b. Will the mass increase, decrease, or stay the
same after mixing? Explain.
You will be able to:
• balance a simple chemical equation
• explain the role of coefficients in chemical
equations
Discussion Notes
A balanced chemical equation is one that shows
the true mathematical relationship between the
reactants and the products in a chemical reaction.
Discussion Notes (cont.)
CH4(g) + O2(g)  CO2(g) + H2O(g)
Inventory of Atoms
Reactants
Products
1C
1C
4H
2H
2O
3O
Discussion Notes (cont.)
CH4(g) + O2(g)  CO2(g) + 2H2O(g)
Inventory of Atoms
Reactants
Products
1C
1C
4H
4H
2O
4O
Discussion Notes (cont.)
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Inventory of Atoms
Reactants
Products
1C
1C
4H
4H
4O
4O
Discussion Notes (cont.)
Discussion Notes (cont.)
There are two types of numbers in a chemical
equation: coefficients and subscripts.
Coefficients: The coefficients in a chemical
equation are the numbers in front of the chemical
formulas of the reactants and products. They show
the correct ratio in which the reactants combine to
form the products.
The coefficients in a chemical equation indicate
how many “units” of an element or a compound
you have.
Wrap Up
How do you balance atoms in a chemical equation?
• In order for matter to be conserved, the number
of atoms on both sides of a chemical equation
must be equal.
• When a chemical equation is balanced, it
indicates how many molecules or moles of each
substance take part in a reaction and how many
molecules or moles of the product(s) are
produced.
Check-in
Balance this equation:
Ca(s) + O2(g)  CaO(s)
Lesson 6: What’s Your Reaction?
Types of Reactions
Day 6 ChemCatalyst
Consider these reactions:
CaCO3(aq)  CaO(aq) + CO2(g)
CO2(g) + NaOH(aq)  NaHCO3(aq)
a. How are these two reactions different?
b. How would you describe, in words, what
happens to the reactants in each case?
Key Question
How do atoms rearrange to form new products?
You will be able to:
• identify patterns in chemical equations that
reflect different types of reactions
• classify chemical equations as representing
combination, decomposition, single exchange,
or double exchange reactions
Prepare for the Activity
Work in pairs.
Discussion Notes
Combination
CO2(g) + NaOH(aq)  NaHCO3(aq)
Decomposition
CaCO3(aq)  CaO(aq) + CO2(g)
Single
replacement
Cl2(g) + 2NaBr(s)  2NaCl(s) + Br2(l)
Double
replacement
2AgCl(s) + BaBr2(aq)  2AgBr(s) +
BaCl2(aq)
Discussion Notes (cont.)
Combination
A + B  AB
Decomposition
AB  A + B
Single
replacement
A + BC  AC + B
Double
replacement
AB + CD  AD + CB
Discussion Notes (cont.)
Chemical reactions can be divided into
categories based on how the atoms in the
reactants rearrange to form the products.
Combination reaction: Several reactants
combine to form a single product. Combination
reactions are easy to spot because there is only
one compound on the product side of the
equation. The general reaction can be written as
A  B  AB.
Discussion Notes (cont.)
Decomposition reaction: A compound breaks
down as a result of the chemical change.
Decomposition reactions are easy to spot
because there is only one reactant. The general
reaction can be written as AB  A  B.
Discussion Notes (cont.)
Single exchange reaction: A compound breaks
apart, and one part combines with the other
reactant—either an atom or a group of atoms
such as OH-, CO32-, or NO3. Typically, one of the
reactants is an element. The general reaction
can be written as A  BC  AC  B, where A
displaces B.
Discussion Notes (cont.)
Double exchange reaction: Both reactants
break apart. Their parts then recombine into two
new products. Thus, the two reactants exchange
parts. The general reaction can be written as
AB + CD  AD + CB, where B and D exchange
with each other (or A and C exchange with each
other).
Discussion Notes (cont.)
Toxins can react in any of these ways in the
body, depending on the toxin and the
circumstances.
Wrap Up
How do atoms rearrange to form new products?
• Chemical reactions can be sorted into categories
based on how the atoms in the reactants
rearrange to form the products.
• Four general types of chemical reactions are
combination reactions, decomposition reactions,
single exchange reactions, and double exchange
reactions.
Check-in
Examine this chemical equation, which describes a
double replacement between silver nitrate and
sodium chloride. Predict the products. Make sure
the equation is balanced.
AgNO3(aq)  NaCl(aq)  Ag____(s) +
Na_____(aq)
Lesson 19: pHooey!
[H+] and pH
Day 8 Chemcatalyst
How is pH related to the acid or base
concentration of a solution?
Discussion Notes
The pH scale is a logarithmic scale that
describes the concentration of H+ ions in
solution.
pH is related to [H+] by the formula
pH = -log [H+]
Discussion Notes (cont.)
H+ concentration
OH– concentration
pH
1.0 X 100 M
1.0 X 10–14 M
0
1.0 X 10–1 M
1.0 X 10–13 M
1
1.0 X 10–2 M
1.0 X 10–12 M
2
1.0 X 10–3 M
1.0 X 10–11 M
3
1.0 X 10–4 M
1.0 X 10–10 M
4
1.0 X 10–5 M
1.0 X 10–9 M
5
1.0 X 10–6 M
1.0 X 10–8 M
6
1.0 X 10–7 M
1.0 X 10–7 M
7
1.0 X 10–8 M
1.0 X 10–6 M
8
1.0 X 10–9 M
1.0 X 10–5 M
9
1.0 X 10–14 M
1.0 X 10–0 M
14
More
acidic
neutral
More basic
Discussion Notes (cont.)
In any solution, the product of the hydrogen ion, H+,
concentration and hydroxide ion, OH–,
concentration is a constant.
Water dissociates into H+ and OH– ions.
Wrap Up
How is pH related to the acid or base concentration
of a solution?
• The pH scale is a logarithmic scale that
describes the concentration of hydrogen ions, H+,
in solution: pH = -log [H+].
• The H+ concentration is related to the OH–
concentration: [H+][OH–] =10–14. So, as [H+]
increases, [OH–] decreases, and vice-versa.
• The pH of water is 7. In water the H+
concentration is equal to the OH– concentration.
Thus, water is neutral.
Check-in
If you know the pH of a solution, what else do you
know?
Lesson 21: Neutral Territory
Neutralization Reactions
Day 11 ChemCatalyst
Excess stomach acid, HCl, can cause extreme
discomfort and pain. Milk of magnesia, Mg(OH)2,
is often taken to reduce stomach acid.
a. What products do you think are produced
when Mg(OH)2 and HCl are mixed?
b. What products do you think are produced
when HNO3 and HCl are mixed?
Key Question
What happens when acids and bases are mixed?
Discussion Notes
A neutralization reaction between a strong acid and
a strong base in aqueous solution produces an
ionic compound (salt) and water.
A neutralization reaction can be described as a
double exchange reaction in which the two
compounds exchange cations.
Wrap Up
What happens when acids and bases are mixed?
• A neutralization reaction between a strong acid
and a strong base produces an ionic salt and
water.
• When strong acids and bases are mixed, the pH
of the product approaches 7 at 25 °C.
Lesson 22: Drip Drop
Titration
Key Question
How can a neutralization reaction help you figure
out acid or base concentration?
Day 12 ChemCatalyst
Sulfuric acid, H2SO4(aq), reacts with magnesium
hydroxide, Mg(OH)2(aq). Write a balanced equation
for the reaction that occurs.
You will be able to:
•
•
explain and complete a titration procedure
use titration data to determine the molarity of a
solution whose concentration is unknown
Prepare for the Lab
Work in pairs.
Wear safety goggles at all times.
Acids and bases are corrosive. Do not get any on
skin or near eyes.
In case of a spill, rinse with large amounts of water.
Discussion Notes
The chemical equation for the neutralization
reaction shows the ratio in which the substances
combine.
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Discussion Notes (cont.)
A titration is a procedure in which a
neutralization reaction is monitored
with an indicator allowing you to
calculate the unknown concentration
of an acid or base.
When the equivalence point is
reached in a titration between a
strong acid and a strong base, the
number of moles of H+ ions equals
the number of moles of OH– ions.
Wrap Up
How can a neutralization reaction help you figure out
acid or base concentration?
• A titration is a procedure that allows you to
calculate the unknown concentration of an acid
or a base using a neutralization reaction.
• During a titration, an indicator is used to signal
when the equivalence point has been reached.
Day 13 ChemCatalyst
A beaker has 50 drops of HCl, along with a drop of
phenolphthalein indicator.
After 100 drops of 0.10 M NaOH are added, the
color changes from clear to bright pink. What is the
concentration of the original HCl solution?