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3.53: Properties of Bases

Difficulty Level: At Grade Created by: CK-12
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This big block of baking chocolate may make your mouth water, but if you were to taste it, you would be in for an unpleasant surprise. The block is 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:

NaOH \mathrm{\overset{H_2O}{\rightarrow}} 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?

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 below . 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

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 below .

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.
  • 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.mcwdn.org/chemist/acidbase.html

Review

  1. What is a base?
  2. What are some properties of bases?
  3. How can you use litmus paper to detect a base?
  4. Ocean water is slightly basic. What might its pH value be?
  5. Considering the properties of bases, which of the following do you think is a base?
    1. orange juice
    2. lemonade
    3. vinegar
    4. baking soda

Vocabulary

base

base

Ionic compound that produces negative hydroxide ions (OH-) when dissolved in water.

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Difficulty Level:

At Grade

Grades:

7 , 8

Date Created:

Nov 14, 2012

Last Modified:

Nov 28, 2014
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