Properties of Bases Jean Brainard, Ph.D. Say Thanks to the Authors

Properties of Bases
Jean Brainard, Ph.D.
Say Thanks to the Authors
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Printed: December 8, 2013
AUTHOR
Jean Brainard, Ph.D.
www.ck12.org
C ONCEPT
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Concept 1. Properties of Bases
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Properties of Bases
Define base.
Identify properties of bases.
Describe how to detect and measure the strength of bases.
List some uses of bases.
These blocks of baking chocolate may make your mouth water, but if you were to taste them, you would be in for
an unpleasant surprise. The blocks are unsweetened chocolate. Without any added sugar, chocolate tastes bitter.
Chocolate tastes bitter because it’s a base.
What Are Bases?
Bases are ionic compounds that produce negative hydroxide ions (OH− ) when dissolved in water. An ionic compound contains positive metal ions and negative nonmetal ions held together by ionic bonds. (Ions are atoms that
have become charged particles because they have either lost or gained electrons.) An example of a base is sodium
hydroxide (NaOH). When it dissolves in water, it produces negative hydroxide ions and positive sodium ions (Na+ ).
This can be represented by the equation:
H O
2
NaOH →
OH− + Na+
Properties of Bases
All bases share certain properties, including a bitter taste. (Warning: Never taste an unknown substance to see
whether it is a base!) Bases also feel slippery. Think about how slippery soap feels. That’s because it’s a base.
In addition, bases conduct electricity when dissolved in water because they consist of charged particles in solution.
(Electric current is a flow of charged particles.)
Q: Bases are closely related to compounds called acids. How are their properties similar? How are they different?
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A: A property that is shared by bases and acids is the ability to conduct electricity when dissolved in water. Some
ways bases and acids are different is that acids taste sour whereas bases taste bitter. Also, acids but not bases react
with metals. For other differences between bases and acids, as well as why they differ in these ways, read the short
article at this URL: http://www.chem4kids.com/files/react_acidbase.html
Detecting Bases
Certain compounds, called indicators, change color when bases come into contact with them, so they can be used to
detect bases. An example of an indicator is a compound called litmus. It is placed on small strips of paper that may
be red or blue. If you place a few drops of a base on a strip of red litmus paper, the paper will turn blue. You can see
this in the Figure 1.1. Litmus isn’t the only detector of bases. Red cabbage juice can also detect bases, as you can
see in this video: http://www.youtube.com/watch?v=vrOUdoS2BtQ&feature=related
MEDIA
Click image to the left for more content.
FIGURE 1.1
Drawing of red litmus paper turning blue
in a base.
Strength of Bases
The strength of bases is measured on a scale called the pH scale, which ranges from 0 to 14. On this scale, a pH
value of 7 indicates a neutral solution, and a pH value greater than 7 indicates a basic solution. The higher the pH
value is, the stronger the base. The strongest bases, such as drain cleaner, have a pH value close to 14.
Uses of Bases
Bases are used for a variety of purposes. For example, soaps contain bases such as potassium hydroxide (KOH).
Other uses of bases can be seen in the Figure 1.2.
Summary
• Bases are ionic compounds that produce negative hydroxide ions (OH-) when dissolved in water.
• Bases taste bitter, feel slippery, and conduct electricity when dissolved in water.
• Indicator compounds such as litmus can be used to detect bases. Bases turn red litmus paper blue.
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Concept 1. Properties of Bases
FIGURE 1.2
• The strength of bases is measured on the pH scale. A pH value greater than 7 indicates a base, and the higher
the number is, the stronger the base.
• Bases have many important uses. For example, they are found in many cleaning products and in concrete.
Vocabulary
• base: Ionic compound that produces negative hydroxide ions (OH− ) when dissolved in water.
Practice
Compare bases with acids at the following URL. Then click on and complete the acids and bases quiz. http://www.m
cwdn.org/chemist/acidbase.html
Review
1.
2.
3.
4.
5.
What is a base?
What are some properties of bases?
How can you use litmus paper to detect a base?
Ocean water is slightly basic. What might its pH value be?
Considering the properties of bases, which of the following do you think is a base?
a.
b.
c.
d.
orange juice
lemonade
vinegar
baking soda
References
1. Christopher Auyeung. . CC BY-NC 3.0
2. Soap: Ross Elliot; Concrete: [U+677E][U+5CA1][U+660E][U+82B3]; Deodorant: User:Donbert/Wikimedia
Commons. . Soap: CC BY 2.0; Concrete: Public Domain; Deodorant: Public Domain
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