1. 6th Grade Life Science Miss Sauer
ACIDS & BASES
6th Grade Life Science
Miss Sauer

2. Our Goals for This Topic
To determine the difference between Acids & Bases
Describe how pH determines how acidic and basic a solution is.
Discuss the importance of studying Acids & Bases
Explain the significance of acids, bases, and pH to living organisms and the environment.
Perform an experiment dealing with Acids & Bases

3. Question 1
What is the difference between a mixture and a solution? (NY: St 4 KI 6.1c)
In a mixture there are substances that don’t react (do not chemically combine), they are just nearby to each other while in a solution the substances can react in many different ways (chemically combine).

4. Chapter 14, Lesson 4: What Are Acids and Bases?
Main Idea: Acids and bases are two groups of compounds that have different properties from each other. Their strengths are measured with the pH scale.

5. Litmus Paper
Litmus paper comes in blue and red strips. It is used to identify compounds as acids.
Acids turn blue litmus paper red.
Bases turn red litmus paper blue.

6. How Does It Work?
The paper is treated with chemicals that change color to show the pH.
When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.

7. Litmus Paper
Litmus paper comes in blue and red strips. It is used to identify compounds as acids.
Acids turn blue litmus paper red.
Bases turn red litmus paper blue.
Remember:
ABR
BRB

8. Acids and Bases Chemicals may be classed as acids or bases.
Things that are neither acids nor bases are neutral.
pH measures how acidic or basic a solution is.

9. ACIDS
Acid: substance that tastes sour and turns blue litmus paper red when dissolved in water.
Acids add hydrogen ions (H+) when they dissolve in water.

10. ACIDS Examples: Lemon juice contains a weak acid called citric acid
Vinegar contains a weak acid called acetic acid
Your stomach uses hydrochloric acid to digest food

11. Acids and Bases
Some of our favorite foods make our tongue curl up because they are SOUR.
Lemons
Pickles

12. Acids
Acid: substance that tastes sour and turns blue litmus paper red when dissolved in water.
Acids add hydrogen ions (H+) when they dissolve in water.
Examples: Lemon juice contains a weak acid called citric acid
Vinegar contains a weak acid called acetic acid
Your stomach uses hydrochloric acid to digest food

13. Acids Often taste sour Strong acids can burn skin & eyes
Strong acids can dissolve metals
Examples:
Lemon juice
Vinegar
Car battery acid (dangerous!)

14. What Are Acids?
An acid is a compound that dissolves in water to make a particular kind of solution.
Chemically, an acid is any substance that produces hydronium ions (H3O+) when dissolved in water.

15. What Are Acids? Some properties of acids are:
Acids create the sour taste in food, like lemons.
Acids react with metals to produce hydrogen (H2) gas.
Acids change the color of blue litmus paper to red.
Acids can be very corrosive, destroying metals and burning skin through chemical action.

16. BASES
Base: substance that feels slippery, tastes bitter, and turns red litmus paper blue when dissolved in water.
Bases add hydroxide ions (OH-) in water.

17. Bases
A base is any substance that dissolves in water and produces hydroxide ions (OH-).

18. What are Bases? Some properties of bases are:
Bases create a bitter taste.
Bases have a slippery feel, like soap.
Bases change the color of red litmus paper to blue.
Bases can be very corrosive, destroying metals and burning skin through chemical action.

19. Bases Can taste bitter, sweetish, or salty
Strong bases can burn skin & eyes
Bases react more easily with protein than with metal; they are often used for cleaning
Examples:
Milk
Baking soda
Soap
Drain cleaner (dangerous!)

20. Definitions of Acids and Bases
An acid is a substance that breaks into ions in an aqueous solution.
A Base (alkaline) is a substance that breaks into ions in an aqueous solution.
Note: aqueous solution is any solution where is the solvent.

21. Acids & Bases
Acids and bases react easily with other substances and with each other. Strong acids and bases can be dangerous and even poisonous.
Example: sulfuric acid from a car battery will burn your skin. Products that contain strong acids or bases are packaged with warning labels.

22. Both hydrogen ions and hydroxide ions are very unstable
Both hydrogen ions and hydroxide ions are very unstable. They combine with other substances very quickly.

23. When an acid and a base react with each other, H+ ions in the acid and OH- ions in the base combine to form neutral water. A compound called a salt is also formed. This reaction is called neutralization.

24. Some substances are not really an acid or a base: For example, PURE water

25. Acids & Bases
One of the most important properties of water is its ability to act as both a weak acid or as a weak base.
In the presence of an acid, water acts as a base.
In the presence of a base, water acts as an acid.

27. Most Substances: Can be identified as either acidic or basic
Like the soil in our backyard.

28. H+ & OH-
Both hydrogen ions and hydroxide ions are very unstable. They combine with other substances very quickly.

29. Neutralization
When an acid and a base react with each other, H+ ions in the acid and OH- ions in the base combine to form neutral water. A compound called a salt is also formed. This reaction is called neutralization.
H + OH H2O

30. pH: system for measuring the strength of different acids and bases.
pH = potential hydrogen
Low pH means a high concentration of hydrogen ions.
High pH means a low concentration of hydrogen ions.

31. pH Scale:
The range of pH is typically from 0 to 14. Acids have a pH between 0 and <7 (0 – 6.9). Bases have a pH between >7 and 14 (7.1 – 14).

32. Did we Miss something?? What happens when the pH of a substance is 7?
Ans: A pH level of 7 indicates a Neutral Substance i.e: Water!

33. Water has a pH of 7. Water is neutral.
It has equal concentrations of hydrogen ions and hydroxide ions.

34. The pH Scale pH scale ranges from 0 -14
pH 7 is neutral; neither acid nor base
Pure water is pH 7
Low pH 0 - <7 (0-6.9) = acid
High pH >7 – 14 (7.1-14) = base
The closer to the ends of the scale, the stronger the solution is

35. 0--------------7---------------14
Acid
Any substance which has a pH of value of less than 7 (0 – 6.9) is considered an acid
Acid Neutral Base

36. 0--------------7---------------14
Base
Any substance which has pH value greater than 7 (7.1 – 14) is a base
Acid Neutral Base

37. pH 7 A pH of 7 is called neutral—neither acid nor base.
Acid Neutral Base

38. Indicator: chemical that changes color when mixed with an acid or a base.
Used to determine the pH of a solution.
Example: The chemical in Litmus Paper is an indicator that changes color in any solution that is not neutral (pH of 7).

39. Acids & Bases STRONG vs WEAK H2SO4 NaOH HI KOH HBr Ca(OH)2 HCl Sr(OH)2
_ completely ionized _ partially ionized
_ strong electrolyte _ weak electrolyte
_ ionic/very polar bonds _ some covalent bonds
Strong Acids: Strong Bases:
HClO4 LiOH
H2SO4 NaOH
HI KOH
HBr Ca(OH)2
HCl Sr(OH)2
HNO3 Ba(OH)2

40. Acids and bases
The pH is a measure of how acidic (H+) or basic (-OH) a solution is.
A scale with values ranging from below 0 to above 14 is used to measure pH.
More acidic
More basic
Neutral

41. Acids and bases
Acids have a lot of Hydrogen ions (H+) and bases have a lot of Hydroxide ions (-OH).
A solution is neutral if its pH equals seven.
More acidic
More basic H+
Neutral H+ H+ H+
-OH
-OH H+
-OH H+
-OH H+
-OH H+ H+ H+ H+
-OH
-OH H+ H+
-OH
-OH H+ H+ H+
(H+) + (-OH) =
H2O
-OH
-OH
-OH H+ H+ H+
-OH H+ H+
-OH H+ H+
-OH
-OH
-OH H+ H+

42. What is the pH scale?
The pH scale measures how acidic or basic a solution is.

43. The pH scale
The pH scale is the concentration of hydrogen ions in a given substance.

44. The pH scale pH = - log [H3O+] 1 2 3 4 5 6 7 8 9 10 11 12 13 14
The pH scale ranges from 1 to mol/L or from 1 to 14.
pH = - log [H3O+]
acid neutral base

45. The pH Scale Each pH unit is 10 times as large as the previous one
A change of 2 pH units means 100 times more basic or acidic
x10
x100

46. 7
Acid
Base
pH Scale 14
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515

47. pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335

48. pH of Common Substance 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1
pH [H1+] [OH1-] pOH
14 1 x x
13 1 x x
12 1 x x
11 1 x x
10 1 x x
9 1 x x
8 1 x x
6 1 x x
5 1 x x
4 1 x x
3 1 x x
2 1 x x
1 1 x x
0 1 x x
NaOH, 0.1 M
Household bleach
Household ammonia
Lime water
Milk of magnesia
Borax
Baking soda
Egg white, seawater
Human blood, tears
Milk
Saliva
Rain
Black coffee
Banana
Tomatoes
Wine
Cola, vinegar
Lemon juice
Gastric juice
More basic
7 1 x x
More acidic

49. The pH Scale

50. To Use pH Paper Place the edge of the pH paper into the mixture.
Observe the color change of the pH paper
Match the resulting color to the colors listed on the outside of the pH paper package.
The colors match with a correlated pH number.
The number is the pH value of the sample.

51. Acids and bases Substances with a pH above 7 (7.1 – 14) are basic.
A base is any substance that forms hydroxide ions (-OH) in water.
Ammonia (pH 11)

52. Acids and bases Substances with a pH below 7 (0 – 6.9) are acidic.
An acid is any substance that forms hydrogen ions (H+) in water.
Vinegar (pH 3)

53. Why is pH important? Fish can’t live if the pH is too high or too low
Soil has to be in a certain pH range for plants to grow and stay healthy.

54. pH and People
Water that has too high or low pH contains harmful dissolved chemicals.
Water plant operators keep a careful watch on the pH of our drinking water, to keep it safe.
Heavy metals, such as lead, react to changes in pH. Environmental regulations require drinking water to remain within a specific pH range to prevent lead and other metals from dissolving out of pipes and containers and entering the water.

55. pH in the Environment
The pH of soil directly affects the availability of nutrients for plants.
Blueberries grow best in what pH soil?

56. pH in the Environment The pH of water directly affects aquatic life.
How are frogs and amphibians sensitive to pH changes?

58. Acids and bases in your body
Many reactions, such as the ones that occur in your body, work best at specific pH values.

59. pH and blood
The pH of your blood is normally within the range of 7.3–7.5.
Holding your breath causes blood pH to drop.
High blood pH can be caused by hyperventilating.

60. Importance of pH in the natural world
Acids and bases can also cause many substances to fall apart because they can force the bonds to break by taking away Hydrogens and Hydroxides from them to make water.
Acids and bases are used in cooking, cleaning, making computers, batteries, enzyme reactions in your body, digestion, and countless other things.

61. Importance of pH in the natural world
Excess Carbon Dioxide production as a result of burning fossil fuels increases the amount of acid rain in the atmosphere. When this rain comes down it kills trees and fish by changing the pH values of their habitat. This affects humans indirectly by limiting the amount of oxygen that can be recycled back into the atmosphere and in our dependency on fish as food or fish meal.

62. pH Facts Item pH Human Blood 7.41 Ocean Water 8.2 Acid Rain < 5.6
Milk
~ 6.4
Beer
4-5
Vinegar
~ 3
Bottled/Distilled water
~ 4.5

63. Question 2
What are acids and bases? Give examples.
An acid basically has an excess of Hydrogen ions (H+) and a base has an excess of Hydroxide ions (-OH) .
Examples can be: lemon juice, ammonia, vinegar, drinking water, hydrated lime, clorox, drano, seltzer water, etc.

64. ACID
Adds Hydrogen Ions H+
Hydrochloric Acid
HCl H+
+ Cl-

65. BASE
Adds Hydroxyl Ions
OH-
Sodium Hydroxide
NaOH
Na+ +
OH-

66. acid + base water + salt + heat?
Acid + Base =
H+ + OH-
H2O
HCl + NaOH
H2O
+ NaCl
+ energy
acid + base water + salt + heat
NEUTRAL

67. Neutralization reactions
When acid and base solutions are mixed in the right proportions, the positive ions from the base combine with the negative ions from the acid.
A new ionic compound forms and water is one of the products.
This is a neutralization reaction.

69. Neutralization reaction
Neutralization goes on in your body every day as food and digestive fluids leave the stomach.
Having soil that is too acidic is a common problem in the U.S. for farmers and gardeners.

70. NEUTRALIZATION
Addition of an acid or alkali (base) to a liquid to cause the pH
of the liquid to move towards a neutral pH of 7.0.

71. pH Scale
Increasing Acidity
Increasing Basicity
NEUTRAL
pH =
[H+] =
[OH-]=

72. Increasing Alkalinity
Increasing Acidity
1 X 10o X 10-14
1 X X 10-13
1 X X 10-12
1 X X 10-11
1 X X 10-10
1 X X 10-9
1 X X 10-8
1 X X 10-7
1 X X 10-6
1 X X 10-5
1 X X 10-4
1 X X 10-3
1 X X 10-2
1 X X 10-1
1 X X 100 H+
5% Sulfuric Acid 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Lemon juice
Orange juice
milk
water
Neutral
Body fluids
Increasing Alkalinity
Egg white
Milk of magnesia
Milk of lime
4% caustic soda
OH-

73. A Chemical Reaction!!! Do now:
What happens when you combine baking soda and vinegar?
A Chemical Reaction!!!

74. Answer
The reaction between baking soda (NaHCO3) and vinegar (CH3COOH) is actually two reactions, an acid base reaction followed by a decomposition reaction. 1) When the two ingredients are mixed, hydrogen ions ( H+) from the vinegar react with the bicarbonate ions (HCO3- ) from the baking soda to form a new chemical called carbonic acid (H2CO3). 2) The carbonic acid thus formed then immediately decomposes into carbon dioxide gas (CO2) and water (H2O). H2CO3 ---> H2O + CO2 It's this carbon dioxide gas that you see bubbling and foaming as soon as you mix baking soda and vinegar together.

75. Acid Rain:
Normal rain has a pH of about 5.5.
Rain is acidic because it contains dissolved carbon dioxide, which combines with water to form a weak acid. However, certain pollutants can lower the pH of rain even further. This causes acid rain. Acid rain can be in the form of rain, snow, sleet, or other precipitation. The most acidic rain has a pH of about 4.3.

76. Cause of Acid Rain:
Main cause is the burning of coal, oil, and gasoline. These fuels release gases that contain sulfur and nitrogen compounds. In the air, they mix with water to form droplets of sulfuric acid and nitric acid. Eventually, they fall as acid rain.

77. Acid Rain’s Affect on the Environment:
Acid rain harms the environment in many ways.
It lowers the pH of both water and land. In lakes and streams, low pH can harm fish. Most fish eggs can’t hatch if the pH is 5 or below. Some lakes are so acidic they have no fish at all.

78. Acid Rain’s Affect on the Environment: (continued)
Acid rain can also harm trees. It damages leaves and needles, weakening the trees and slowing their growth.
Acid rain may also dissolve and wash away nutrients from the soil before trees and other plants can use them to grow.

79. Acid Rain’s Affect on the Environment: (continued)
Acid rain affects building materials, such as metals, stone, and paints. Limestone and marble are often used in statues, monuments, and buildings. Acid rain will slowly dissolve the stone causing damage.

80. There is a pile of weathered material at the bottom
There is a pile of weathered material at the bottom. It is slowly being eroded down hill by gravity.
Mount Rushmore
It will not be there forever!!
***However, maintenance is done to maintain it***

81. Acid Rain Today:
Thanks to the Clean Air Act and other laws, acid rain is less of a problem today than in years past.

82. Test Your Knowledge What is the range of an ACID on the pH scale?
Ans: 0-<7 (0 – 6.9)
What is the range of a BASE and what is another name for a BASE?
Ans: >7-14 (7.1 – 14), Alkaline

83. Characteristics Of Acids
Acids can be characterized by:
A sour taste.
It turns blue litmus paper red
It tastes sour. Try drinking lemon juice (citric acid)

84. Characteristics of Bases
A Base is characterized by:
A bitter taste. (Milk of Magnesia)
It feels slippery. (Soapy Water)
It turns Red Litmus Blue.

85. Closure Questions What is an acid? What is a base?
What is litmus paper?
What is an indicator?
What does it mean to be neutral on the pH scale?
What does pH mean?
What is the range of the pH scale?
What is the range for an acid on the pH scale?

86. Closure Questions What is the range for an base on the pH scale?
Which turns blue litmus paper red?
Which turns red litmus paper blue?
Give an example of an acid and a base.
What is the pH of normal rain?
What are the main causes of acid rain?

87. Closure Questions What is the hydrogen (H+) ion associated with?
What is the hydroxide (OH-) ion associated with?