What is pH?
The definition:
pH is the numerical measure of acidity of a solution. The pH scale is a scale used to measure the acidity of a solution. The pH scale was created by Sorensen in 1909. pH is short for “potential of hydrogen” or “power of hydrogen.”

How it the scale works:
There are no limits on the scale so the acidity levels can range from greater than 14 to a substance with a negative pH though most range from 0-14. Solutions with a pH lower than 7 are considered acidic and a solution with a pH that is greater than 7 is considered alkali. If the solution is at the midpoint of the scale at 7 it is neutral. The lower the pH is the more acidic a solution is, and the higher the more alkali.
Figure 1. What litmus paper looks like

litmus paper diagram.jpg

Acids and bases:
Weak acids are things like lactic acid that can be found in sour milk, tartaric acid in grapes and apples, and a common one called citric acid that can be found in citrus fruits like lemons and limes. An acid is defined as a substance that contains hydrogen that breaks up in water. A base is defined as a substance containing the hydroxide ion, OH. When an acid and a base are put together, they react to form compounds that are called salts. The reaction of the sodium hydroxide and sulfuric acid produces a neutral salt solution.
Figure 2. How acids and bases react to each other
acids and bases diagram.jpg

Other ways to measure acidity:
Litmus paper is a common indicator of if a solution is alkali or acidic. In an acidic solution when you put the paper in ilitmuspaper.jpgt will turn red and in a basic solution the paper will turn blue. If the solution gives the paper
a half way color in between blue and red, the solution is neutral. An example of a neutral solution is pure water.

Figure 3. litmus paper
Acidity in soil and polluted water:
It is important to measure the acidity in the soil of were a farmer will grow a crop. This is important because they need to know what adjustments need to be made to the soil for the crop to grow big and healthy. Some plants can and will grow healthy in acidic soil, but many plants don’t. Acidic soils are often considered unfertile but can be “sweetened” or treated with lime neutralizing the soil. Like the acidity in soil, in polluted water or water with acid in it can be neutralized with lime. Lime is an alkali that is used to treat anything from soil to water with too much acid in it. The lime neutralizes the acid in the substance. Lime is the compound calcium hydroxide and like all of the other alkali it will produce hydrogen ions in solution.

A real life example:
An example of acids and bases in real life are hydrangeas. Hydrangeas are a good example because they like many plants are sensitive to the amount of base or acid in the soil. The color is sensitive and will change due to the type of soil. Hydrangeas are a blue color in acidic soil and in a more basic or alkaline soil they are pinker.

To learn more about pH visit theese links:
What are acids and bases? Part 1
What are acids and bases? Part 2
What are acids and bases? - R
What is pH? Part 1
What is pH? Part 2
Alkali: alkali means that the solution is a base.
Lime: lime is a alkali or a base that neutralizes anything with too much acid in it.
Hydrogen: hydrogen is a chemical element that has a symbol that is an upper case H and an atomic number 1.
pH: the pH is the amount of acidity in a solution.

Encyclopedia Britannica:
"acid and base." Compton's by Britannica. Encyclopedia Britannica Online School Edition.Encyclopedia Britannica, Inc., 2012. Web. 24 Sept. 2012.
“Chemistry” by: eyewitness science:
Newmark, Ann. ‘Chemistry” acids and bases.1st American ed.LondonDorlingKindersley 1993.
“The way science works”
Kerrod, Robin and Holgate, Sharon Anne. ‘The way science works” Acids and Bases. 1st American ed. New York, NY: DK Publishing, 2002..
Wikipedia contributors. "PH." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 23 Sep. 2012. Web. 25 Sep. 2012.