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What are Acids and Bases? --------- What is pH?

What is an Acid?

An acid is something that has a pH less than 7.0 . The chemistry definition of an acid is: "a substance that donates a hydrogen ion (H+) to another substance, which is called a base. (Or give out hydrogen ions when dissolved in water.)"

What are the properties of acids?

1) Acids taste sour when they are eaten can sting the skin when they are touched

2) Acids can corrode (or eat away at) metals and skin.

3) Acids can be used as a reactant during electrolysis.

4) Acids will turn blue litmus paper red.

What is a Base?

A base (in chemistry) means having a pH (on the pH scale) of 8-14.It is a substance that can accept protons. A base that is dissolved in water is called an alkali.

What are the properties of bases?

Bases have a bitter taste (opposed to sour taste of acids)

Bases fee; slimy, or soapy feel on fingers

Bases turn red litmus paper blue

If mixed with an acid, bases will reduce the pH value.

If touched, it may cause a skin irritation.

What is pH?

The pH scale measures how acidic an object is. Objects that are not very acidic are called basic. The scale has values ranging from zero (the most acidic) to 14 (the most basic).

Look at the scale on the left. You can see the pH of pure water has a pH value of 7. This value is considered neutral—neither acidic or basic. Normal, clean rain has a pH value of between 5.0 and 5.5, which is slightly acidic. However, when rain combines with sulfur dioxide or nitrogen oxides—produced from power plants and automobiles—the rain becomes much more acidic.

Typical acid rain has a pH value of 4.0. A decrease in pH values from 5.0 to 4.0 means that the acidity is 10 times greater.

How pH is Measured

There are many high-tech devices that are used to measure pH in laboratories. One easy way that you can measure pH is with a strip of litmus paper. When you touch a strip of litmus paper to something, the paper changes color depending on whether the substance is acidic or basic. If the paper turns red, the substance is acidic, and if it turns blue, the substance is basic.







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