What is acid and how do you know it?

Robert Angus Smith, a Scottish chemist, was the first to use the phrase "acid rain" in 1852. He noticed that the bricks in the buildings were falling apart, and through scientific experimentation, later found that there was a connection between London’s polluted skies and the pH of its rainfall. Most scientists today agree that normal rainfall is slightly acidic with a pH of 5.6. The rain naturally reacts with carbon dioxide in the atmosphere to form a weak carbonic acid. Therefore, scientists define acid rain as any wet precipitation (rain, sleet, and snow) with a pH of less than 5.6. The rain becomes more acidic when it reacts with other gases in the atmosphere such as sulfur dioxide and nitrogen oxides. These other gases are naturally present in the atmosphere in small amounts; Industrial activities have increased their amounts.  
 
Tools and things you will need - Glass or plastic bowl; litmus paper; measuring cup; stirring rod; vinegar, lemon juice, baking soda, chalk, milk of magnesia, cola, or coffee - a few drops of each 
 
What to do? 
 1. Get a cup of water out of your local creek and pour it into a bowl. 
 2. Wash and dry the measuring cup. 
 3. Test the pH of the water with litmus paper (acids turn the paper pink). 
 4. Measure out one cup of baking soda. 
 5. If the water is acid (pH less than 7), slowly stir baking soda into the bowl. 
 6. Test with new litmus paper periodically until the paper turns blue. (This happens when the acid is neutralized.) 
 7. Repeat with a variety of acids (lemon juice, cola, and coffee) and a variety of bases (milk, milk of magnesia, and chalk). 
 

What did you see? 

 1. How much baking soda was needed to neutralize your creek water, coke, lemon juice etc.? 
 2. What happened when you combined two different acids? 
 3. What else did you see? 
 

What do you conclude? 

 1. Which substance had the highest pH (was the most basic)? 
 2. What are your conclusions? "Write down what think." 
 

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