1. Investigation IV: Neutralizing Toxins
Toxins Unit
Investigation IV: Neutralizing Toxins
Lesson 1: Heartburn
Lesson 2: Watered Down
Lesson 3: pHooey!
Lesson 4: Proton Shuffle
Lesson 5: Neutral Territory
Lesson 6: Drip Drop
Lesson 7: Call Poison Control

2. Toxins Unit – Investigation IV
Lesson 1:
Heartburn

3. ChemCatalyst
Countless products are advertised on TV with the promise of reducing acid indigestion.
What is acid indigestion? What is acidity?
What does acid have to do with your stomach?
How do you think acid “reducers” work?
Unit IV • Investigation IV-X

4. The Big Question
What are some characteristics of solutions that are acidic, basic, or neutral?
Unit IV • Investigation IV-X

5. You will be able to:
Describe the differences among acidic, basic, and neutral solutions.
Unit IV • Investigation IV-X

6. Notes
Indicators: A set of substances that respond to other substances with vivid color changes.
Unit IV • Investigation IV-X

7. Activity
Purpose: This activity will introduce you to a special category of solution.
(cont.)
Unit IV • Investigation IV-X

8. (cont.)
Safety note: Do not get acids and bases on your skin. In case of a spill, rinse with large amounts of water. Wear goggles.
(cont.)
Unit IV • Investigation IV-X

9. Formula Cabbage Juice Indicator color Indicator number
Substance
Formula
Cabbage Juice
Indicator color
Indicator number
table salt (aq)
NaCl
vinegar (aq)
C2H4O2
rubbing alcohol
C3H8O
ammonium hydroxide (aq)
NH4OH
distilled water
H2O
stomach acid (aq)
HCl
washing soda (aq)
Na2CO3
lemon juice
C6H8O7
drain cleaner (aq)
NaOH
Unit IV • Investigation IV-X

10. (cont.) 14 7
(cont.)
Unit IV • Investigation IV-X

11. (cont.) Observations when added to CaCO3 water stomach acid vinegar
drain cleaner
Unit IV • Investigation IV-X

12. Making Sense
Look for patterns in the names, chemical formulas, uses, and properties of the substances you tested.
List four characteristics of acids.
List four characteristics of bases.
Unit IV • Investigation IV-X

13. Notes
Indicators can be used to identify substances that are acidic, basic, and neutral when dissolved in water.
Acids turn cabbage juice pink and are between 0 and 7 on the universal indicator scale.
Bases turn cabbage juice green or blue and are between 7 and 14 on the universal indicator scale.
Neutral substances do not change color with cabbage juice and are at or very near 7 on the universal indicator scale.
(cont.)
Unit IV • Investigation IV-X

14. (cont.)
pH scale: A number line from 0 to 14. The numbers are associated with indicator colors.
The numbers associated with indicator colors are also called pH numbers or simply pH.
Unit IV • Investigation IV-X

15. Check-In
An unknown substance is purple with cabbage juice and does not react with calcium carbonate. Is it an acid, base or neutral substance? Explain.
Unit IV • Investigation IV-X

16. Wrap-Up
Acids and bases are different types of solutions and are classified according to their observable behavior.
Acids and bases respond differently to indicators. Depending on the indicator, different colors will form that show either an acidic or basic substance.
Unit IV • Investigation IV-X

17. Toxins Unit – Investigation IV
Lesson 2:
Watered Down

18. ChemCatalyst Describe what you observe in the three vials.
What is one explanation for the differences you observe?
If you tested each solution with universal indicator before putting in the gummy bears, what colors would you expect to see?
Unit IV • Investigation IV-X

19. The Big Question
How does dilution affect the acidity or basicity of a solution?
Unit IV • Investigation IV-X

20. You will be able to:
Explain how dilution affects the concentration and pH of a solution.
Unit IV • Investigation IV-X

21. Activity
Purpose: In this activity you will examine the effect of concentration on acidity and basicity of solutions.
(cont.)
Unit IV • Investigation IV-X

22. (cont.)
Safety note – Do not get acids and bases on your skin. In case of a spill, rinse with large amounts of water. Wear goggles.
(cont.)
Unit IV • Investigation IV-X

23. Data Table for dilution of 1.0 M HCl
Well #
Concentration
Color
pH number
1.0 M HCl
0.10 M HCl
0.010 M HCl
M HCl
M HCl
M HCl
M HCl
M HCl
M HCl
Unit IV • Investigation IV-X

24. Data Table for dilution of 1.0 M NaOH
Well #
Concentration
Color
pH number
1.0 M NaOH
0.10 M NaOH
0.010 M NaOH
M NaOH
M NaOH
M NaOH
M NaOH
M NaOH
M NaOH
Unit IV • Investigation IV-X

25. Data Table for dilution of 1.0 M NaCl
Well #
Concentration
Color
pH number
1.0 M NaCl
0.10 M NaCl
0.010 M NaCl
M NaCl
M NaCl
M NaCl
M NaCl
M NaCl
M NaCl
Unit IV • Investigation IV-X

26. Making Sense
What does concentration have to do with the acidity or basicity of a solution?
Unit IV • Investigation IV-X

27. Notes pH scale More H+ More OH– (cont.) 14 7
More H+
More OH–
pH scale
(cont.)
Unit IV • Investigation IV-X

28. Arrhenius definition:
(cont.)
Arrhenius definition:
An acid is any substance that adds a hydrogen ion (H+) to the solution.
A base is any substance that adds a hydroxide ion (OH–) to the solution.
(cont.)
Unit IV • Investigation IV-X

29. (cont.)
HA  H+ + A–
XOH  X+ + OH–
Unit IV • Investigation IV-X

30. Check-In
Lemon juice has a pH of about 2. What does this tell you about what is in the solution?
What would happen if you diluted this solution?
Unit IV • Investigation IV-X

31. Wrap-Up
The acidity and basicity of a solution are related to the concentration of the solution. Dilute solutions are less acidic and basic than more concentrated solutions.
Dilution of an acid or a base results in a solution that is increasingly neutral.
(cont.)
Unit IV • Investigation IV-X

32. The pH scale is related to the concentration of H+ and OH– ions in solution.
According to Arrhenius, an acid is any substance that adds a hydrogen ion (H+) to the solution and a base is any substance that adds a hydroxide ion (OH–) to the solution.
Unit IV • Investigation IV-X

33. Toxins Unit – Investigation IV
Lesson 3:
pHooey!

34. ChemCatalyst Examine the following data: (cont.) Substance pH
0.10 M HCl
1.0
0.010 M HCl
2.0
M HCl
3.0
1.0 M NaOH
14.0
0.10 M NaOH
13.0
0.010 M NaOH
12.0
Water
7.0
(cont.)
Unit IV • Investigation IV-X

35. What do you think pH really represents?
(cont.)
What do you think pH really represents?
How does the concentration of the solutions relate mathematically to the pH of the solutions?
Unit IV • Investigation IV-X

36. The Big Question
How does pH relate to the concentrations of acidic and basic solutions?
Unit IV • Investigation IV-X

37. You will be able to:
Find the pH of a solution if you know the concentrations of hydrogen or hydroxide ions that it contains.
Unit IV • Investigation IV-X

38. Activity
Purpose: You will explore the relationship between pH, pOH, [H+], and [OH–].
(cont.)
Unit IV • Investigation IV-X

39. [H+] (in scientific notation)
Substance
Acidic or Basic? pH
[H+] (in decimal)
[H+] (in scientific notation)
1 M HCl
Stomach acid (0.1 M HCl)
Acidic
0.1 M
1.0  10–1 M
Clear Soda 3
0.001 M
Rain Water
1.0  10–6 M
Distilled Water 7 M
Alcohol
Neutral
Salt Water M
Washing Soda
Basic 8
1.0  10–8 M
Ammonia M
1.0  10–10 M
Drain Cleaner (0.1 M NaOH) 13
1 M NaOH
1.0  M
Unit IV • Investigation IV-X

40. Well pH [H+] [OH–] pOH A 1 1.0  10–1 M 13 B 2 1.0  10–2 M12 C 3
1.0  10–3 M D 4
1.0  10-4 M
1.0  10–10 M 10 E 5
1.0  10–5 M F 6
1.0  10–6 M G 7
1.0  10–7 M H I
HCl
Unit IV • Investigation IV-X

41. Well pH [H+] [OH–] pOH R 7 1.0  10–7 M Q P O 8 1.0  10–8 M N 95 M 10
1.0 x10–10 M L 11
1.0  10–11 M 3 K 12
1.0  10–12 M
1.0  10–2 M J 13
1.0  10–13 M
1.0  10–1 M 1
NaOH
Unit IV • Investigation IV-X

42. Making Sense How are pH and pOH related to each other mathematically?
Unit IV • Investigation IV-X

43. Notes (cont.) pH = 4 pH = 5 pH = 6 pH = 7 Key: H+ Cl–
This box would show 1,000 H+ ions and 1,000 Cl– ions.
This box would show 100 H+ ions and 100 Cl– ions.
(cont.)
Key: H Cl–
Unit IV • Investigation IV-X

44. (cont.) pH = –log[H+] pOH = –log[OH–] (cont.)
Unit IV • Investigation IV-X

45. (cont.) Sample Problem:
What is the pH of a solution with a hydrogen ion concentration of 3.4  10–4 moles/ L?
(cont.)
Unit IV • Investigation IV-X

46. (cont.)
Please be careful when entering scientific notation into your calculator—it is very easy to make a mistake. When entering 3.4  10–4, first enter “3.4”. Then press the button labeled “EXP” or “10X” or “EE”. Now enter –4, using the “+/–“ key, not the subtraction key. Never try to enter this number by pressing “X” and “10” and “–4”.
Unit IV • Investigation IV-X

47. Check-In What is the pH of a solution with [OH–] = 1.0  10–12 M?
Unit IV • Investigation IV-X

48. Wrap-Up
The relationship between pH and pOH of a solution is expressed by the following: pH + pOH = 14.
The relationship between [H+] and [OH–] in a solution is expressed by the following: –log [H+] + –log [OH–] = 14.
The pH of a solution is logarithmically related to the concentration of hydrogen ion and can be calculated mathematically using the following equation: pH = log [H+]
Unit IV • Investigation IV-X

49. Toxins Unit – Investigation IV
Lesson 4:
Proton Shuffle

50. ChemCatalyst
Besides HCl, the digestive system also produces a compound called bicarbonate, HCO3–. Bicarbonate plays a vital role in regulating the pH of the digestive system.
Do you think bicarbonate, HCO3–, is an acidic, basic or neutral substance? Explain your reasoning.
Unit IV • Investigation IV-X

51. The Big Question
Is there a better way to classify acids, bases, and neutral substances?
Unit IV • Investigation IV-X

52. You will be able to:
Explain the behavior of acids and bases on a molecular level.
Unit IV • Investigation IV-X

53. Activity
Purpose: This activity will provide you with information to expand on your definition of acids and bases.
(cont.)
Unit IV • Investigation IV-X

54. (cont.)
Unit IV • Investigation IV-X

55. Making Sense
The Arrhenius definition of acids and bases defines them as substances that release either H+ or OH–. How can we expand on this definition to include substances like methylamine, CH3NH2, and ammonia, NH3?
(cont.)
Unit IV • Investigation IV-X

56. (cont.)
Acids
(cont.)
Unit IV • Investigation IV-X

57. (cont.)
Bases
(cont.)
Unit IV • Investigation IV-X

58. (cont.)
Neutral Substances
Unit IV • Investigation IV-X

59. Notes Brønsted-Lowry definitions
An acid is a substance from which a proton can be removed.
A base is a substance that can remove a proton from another substance.
(cont.)
Unit IV • Investigation IV-X

60. (cont.)
H2O (l)  H+(aq) OH–
(cont.)
Unit IV • Investigation IV-X

61. NH3 (aq) + H2O (l)  NH4+ (aq) + OH– (aq)
(cont.)
NH3 (aq) + H2O (l)  NH4+ (aq) + OH– (aq)
(base) (acid)
HNO3  H+ + NO3–
HNO3 + H2O  H3O+ + NO3–
(acid) (base)
pH = –log[H3O+]
Unit IV • Investigation IV-X

62. Check-In
Do you predict a solution of CH4 to be acidic, basic or neutral? Explain.
Unit IV • Investigation IV-X

63. Wrap-Up
A Brønsted-Lowry acid is a substance from which a proton can be removed.
A Brønsted-Lowry base is a substance that removes a proton from an acid.
When an acid reacts with water, hydronium ion is produced.
Some substances can act as both acid and base.
Unit IV • Investigation IV-X

64. Toxins Unit – Investigation IV
Lesson 5:
Neutral Territory

65. ChemCatalyst
Milk of magnesia, Mg(OH)2, can reduce excess stomach acid, HCl.
What products do you think are produced when Mg(OH)2 and HCl are mixed?
What do you think happens when you add an acid together with a base?
Unit IV • Investigation IV-X

66. The Big Question How do acids and bases interact with each other?
Unit IV • Investigation IV-X

67. You will be able to:
Write balanced chemical equations describing the interactions between acids and bases.
Unit IV • Investigation IV-X

68. Activity
Purpose: In this activity, you will examine the products of reactions between acids and bases.
(cont.)
Unit IV • Investigation IV-X

69. acidic, basic, or neutral
starting solution
pH at start
solution added
pH after mixing
acidic, basic, or neutral
Did a reaction occur?
Reactions with NaOH
0.10 M HCl
0.10 M NaOH
0.10 M HNO3
solid Ca(OH)2 
Reactions with HCl
0.10 M HCl
Unit IV • Investigation IV-X

70. Making Sense
Complete the following set of general equations for the reaction of HCl and NaOH with the “generic” acid HA and the “generic” base MOH.
HA HCl  HA NaOH 
MOH + HCl  MOH + NaOH 
Unit IV • Investigation IV-X

71. Notes
A neutralization reaction is a reaction in which an acid and a base react in aqueous solution to produce a salt and water.
(cont.)
Unit IV • Investigation IV-X

72. (cont.)
HA + MOH  MA + H2O
(cont.)
Unit IV • Investigation IV-X

73. (cont.) 2HCl (aq) + Mg(OH)2  MgCl2 (aq) + 2 H2O (l)
Unit IV • Investigation IV-X

74. Check-In
Sulfuric acid, H2SO4, reacts with magnesium hydroxide, Mg(OH)2. Write a balanced equation for the reaction that occurs.
Unit IV • Investigation IV-X

75. Wrap-Up
A neutralization reaction is a reaction between an acid and a base to produce a salt and water.
When acids are mixed with acids, the pH remains less than 7. When bases are mixed with bases, the pH remains greater than 7.
Unit IV • Investigation IV-X

76. Toxins Unit – Investigation IV
Lesson 6:
Drip Drop

77. ChemCatalyst
A student mixes 100 mL of 0.10 M HCl with different volumes of 0.10 M NaOH.
100 mL of 0.1 M HCl + 50 mL of 0.1 M NaOH
100 mL of 0.1 M HCl mL of 0.1 M NaOH
100 mL of 0.1 M HCl mL of 0.1 M NaOH
(cont.)
Unit IV • Investigation IV-X

78. Which solution is the least toxic?
(cont.)
Which solution is the least toxic?
Are the final solutions acid, basic, or neutral?
Unit IV • Investigation IV-X

79. The Big Question
How can the interactions of acids and bases be used to determine the concentration of a particular acidic or basic solution?
Unit IV • Investigation IV-X

80. You will be able to:
Use the experimental method known as “titration” to determine the unknown concentration of an acid or base.
Unit IV • Investigation IV-X

81. Activity
Purpose: This activity will introduce you to a laboratory procedure used to determine the concentration of an acid or a base.
(cont.)
Unit IV • Investigation IV-X

82. (cont.) (cont.) HCl solution Drops of 0.10 M NaOH added to neutralize
Calculated concentration of HCl
20 drops HCl Solution A
20 drops HCl Solution B
20 drops HCl Solution C
(cont.)
Unit IV • Investigation IV-X

83. Initial HCl concentrat ion
Initial volume of HCl
Volume of M NaOH added
Total moles of NaOH
Total moles of HCl
Initial HCl concentrat ion
1.0 L
moles
0.10 M
100 mL
200 mL
moles
50 mL
moles
0.050 M
73 mL
Unit IV • Investigation IV-X

84. Making Sense
Describe how you determined the concentration of the NaOH solution in Problem 6.
Unit IV • Investigation IV-X

85. Notes
A titration is a method for determining the concentration of an acid or base solution by reacting a known volume of the solution with a solution of known concentration. When the moles of H+ are equal to the moles of OH– in the solution, the reaction has reached the equivalence point of the titration, sometimes referred to as the endpoint.
(cont.)
Unit IV • Investigation IV-X

86. (cont.)
Example:
If mL of 0.50 M nitric acid, HNO3, solution are required to titrate mL of sodium hydroxide, NaOH, what is the molarity of the NaOH?
Unit IV • Investigation IV-X

87. Check-In
You place 50 drops of HCl in a beaker along with a drop of phenolphthalein indicator. After you have added 100 drops of 0.10 M NaOH, the color is a very faint pink.
What is the concentration of the HCl solution?
Unit IV • Investigation IV-X

88. Wrap-Up
A titration is a procedure that allows you to calculate the concentration of an unknown acid or base using a neutralization reaction.
During a titration, when the moles of H+ are equal to the moles of OH– in the solution, the reaction has reached the equivalence point of the titration, sometimes referred to as the endpoint.
Unit IV • Investigation IV-X

89. Toxins Unit – Investigation IV
Lesson 7:
Call Poison Control

90. ChemCatalyst
Imagine that your little brother spilled a toxic substance on his skin. You decide to call Poison Control: 1 (800) 222–1222.
What are some things that you might want to know about the substance?
What kinds of questions do you think Poison Control will ask you? What might they tell you to do? Explain your thinking.
Unit IV • Investigation IV-X

91. The Big Question
How do solubility and pH contribute to the toxicity of a substance?
Unit IV • Investigation IV-X

92. You will be able to:
Use the mole concept and balanced chemical equations to calculate the mass relationships between products and reactants and determine the concentrations or pH of solutions in which the reactions are a part.
Unit IV • Investigation IV-X

93. Activity
Purpose: The purpose of this worksheet is to review some of the key ideas in the Toxins Unit.
Unit IV • Investigation IV-X

94. Making Sense
No Making Sense exercises.
Unit IV • Investigation IV-X

95. Check-In
No Check-In exercise.
Unit IV • Investigation IV-X

96. Wrap-Up
No Wrap-Up points.
Unit IV • Investigation IV-X