http://www.ck12.org Chapter 3. Chemical Interactions
Detecting Acids
Certain compounds, called indicators, change color when acids come into contact with them, so indicators can be
used to detect acids. An example of an indicator is the compound called litmus. It is placed on small strips of paper
that may be red or blue. If you place a few drops of acid on a strip of blue litmus paper, the paper will turn red. You
can see this in theFigure3.97. Litmus isn’t the only indicator for detecting acids. Red cabbage juice also works
well, as you can see in this entertaining video: http://www.youtube.com/watch?v=vrOUdoS2BtQ.
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5011FIGURE 3.97
Drawing of blue litmus paper turning red
in acid.Strength of Acids
The strength of acids is measured on a scale called the pH scale. The pH value of a solution represents its
concentration of hydrogen ions. A pH value of 7 indicates a neutral solution, and a pH value less than 7 indicates
an acidic solution. The lower the pH value is, the greater is the concentration of hydrogen ions and the stronger the
acid. The strongest acids, such as battery acid, have pH values close to zero.
Uses of Acids
Acids have many important uses, especially in industry. For example, sulfuric acid is used to manufacture a variety
of different products, including paper, paint, and detergent. Some other uses of acids are be seen in theFigure3.98.
Summary
- Acids are ionic compounds that produce positive hydrogen ions (H+) when dissolved in water.
- Acids taste sour, conduct electricity when dissolved in water, and react with metals to produce hydrogen gas.
- Certain indicator compounds, such as litmus, can be used to detect acids. Acids turn blue litmus paper red.
- The strength of acids is measured on the pH scale. A pH value less than 7 indicates an acid, and the lower the
number is, the stronger the acid. - Acids have many important uses, especially in industry.