1. Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases
Living By Chemistry
Unit 4: TOXINS
Stoichiometry, Solution Chemistry, and Acids and Bases

2. 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

3. 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?

4. Lesson 1: Toxic Reactions
Chemical Equations

5. 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?

6. Key Question
How do chemists keep track of changes in matter?

7. You will be able to: complete basic translations of chemical equations
give a basic definition of a toxin

8. Prepare for the Demonstration
Work in pairs.

9. 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)

10. Discussion Notes HCl(aq) + NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g)
The chemical equation represents a change in matter using symbols and formulas.

11. 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.

12. 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.

13. Check-in
Consider this reaction between sodium cyanide and a solution of hydrochloric acid:
NaCN(s)  HCl(aq)  NaCl(aq)  HCN(g)
Write an interpretation of the chemical equation.
Sodium cyanide is highly toxic. What is the most likely way it will enter the body?

14. Lesson 2: Making Predictions
Observing Change

15. 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.

16. Key Question
How can you predict what you will observe based on a chemical equation?

17. You will be able to:
relate chemical equations to real-world observations
make predictions based on chemical equations

18. Discussion Notes
AgNO3(aq)  KCl(aq)  KNO3(aq)  AgCl(s)

19. 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.

20. 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.

21. 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)

22. Lesson 3: Spare Change
Physical Versus Chemical Change

23. Key Question
How are changes in matter classified?

24. 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)

25. 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

26. 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.

27. 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.

28. 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)

29. 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.

30. Lesson 4: Some Things Never Change
Conservation of Mass

31. Key Question
How does mass change during a chemical or physical change?

32. Lesson 5: Atom Inventory
Balancing Chemical Equations

33. Key Question
How do you balance atoms in a chemical equation?

34. Day 4 ChemCatalyst Consider this reaction:
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?
Na2CO3(aq) + CaCl2(aq)  2NaCl(aq) + CaCO3(s)

35. 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.

36. 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.

37. Check-in Consider this reaction:
Describe what you will observe when copper (II) carbonate, CuCO3(s), and sulfuric acid, H2SO4(aq), are mixed.
Will the mass increase, decrease, or stay the same after mixing? Explain.
CuCO3(s) + H2SO4(aq)  CO2(g) + CuSO4(aq) + H2O(l)

38. You will be able to: balance a simple chemical equation
explain the role of coefficients in chemical equations

39. Discussion Notes
A balanced chemical equation is one that shows the true mathematical relationship between the reactants and the products in a chemical reaction.

40. Discussion Notes (cont.)
CH4(g) + O2(g)  CO2(g) + H2O(g)
Inventory of Atoms
Reactants
Products
1 C
4 H
2 H
2 O
3 O

41. Discussion Notes (cont.)
CH4(g) + O2(g)  CO2(g) + 2H2O(g)
Inventory of Atoms
Reactants
Products
1 C
4 H
2 O
4 O

42. Discussion Notes (cont.)
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Inventory of Atoms
Reactants
Products
1 C
4 H
4 O

43. Discussion Notes (cont.)

44. 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.

45. 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.

46. Check-in
Balance this equation:
Ca(s) + O2(g)  CaO(s)

47. Lesson 6: What’s Your Reaction?
Types of Reactions

48. Day 6 ChemCatalyst Consider these reactions:
CaCO3(aq)  CaO(aq) + CO2(g)
CO2(g) + NaOH(aq)  NaHCO3(aq)
How are these two reactions different?
How would you describe, in words, what happens to the reactants in each case?

49. Key Question
How do atoms rearrange to form new products?

50. 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

51. Prepare for the Activity
Work in pairs.

52. Discussion Notes CaCO3(aq)  CaO(aq) + CO2(g) 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)

53. Discussion Notes (cont.)
Combination
A + B  AB
Decomposition
AB  A + B
Single replacement
A + BC  AC + B
Double replacement
AB + CD  AD + CB

54. 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.

55. 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.

56. 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.

57. 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).

58. Discussion Notes (cont.)
Toxins can react in any of these ways in the body, depending on the toxin and the circumstances.

59. 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.

60. 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)

61. Lesson 19: pHooey!
[H+] and pH

62. Day 8 Chemcatalyst
How is pH related to the acid or base concentration of a solution?

63. 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+]

64. Discussion Notes (cont.)
More acidic
H+ concentration
OH– concentration pH
1.0 X 100 M
1.0 X 10–14 M
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 7 8 9
1.0 X 10–0 M 14
neutral
More basic

65. 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.

66. 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.

67. Check-in
If you know the pH of a solution, what else do you know?

68. Lesson 21: Neutral Territory
Neutralization Reactions

69. 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.
What products do you think are produced when Mg(OH)2 and HCl are mixed?
What products do you think are produced when HNO3 and HCl are mixed?

70. Key Question
What happens when acids and bases are mixed?

71. 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.

72. 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.

73. Lesson 22: Drip Drop
Titration

74. Key Question
How can a neutralization reaction help you figure out acid or base concentration?

75. Day 12 ChemCatalyst
Sulfuric acid, H2SO4(aq), reacts with magnesium hydroxide, Mg(OH)2(aq). Write a balanced equation for the reaction that occurs.

76. 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

77. 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.

78. Discussion Notes HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
The chemical equation for the neutralization reaction shows the ratio in which the substances combine.
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

79. 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.

80. 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.

81. 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?