Materials
Pink and blue litmus paper
Distilled water
Tap water
Orange juice
Milk
Baking soda
Soda pop
Bleach
Scientific method sheet with predictions

Procedures

What is pH?
Begin by explaining what the pH scale is.  Describe the range of the scale (1 being the strongest acid, 14 being the strongest base, and 7 being neutral).  In making this description, I used a swimming pool and fish tank as an example, since many of the children could relate to these analogies.  Ask the children what an acid is and to give a few examples.  Do the same with a base.  Ask them to give examples of a neutral substance.

How do you tell if something is an acid or a base?
Explain what litmus paper is and how it is used.  Remember if blue litmus turns pink, it's an acid.  If pink turns blue, it's a base.  If neither changes, it's neutral.  Remind the children they must try both pieces of litmus, pink and blue, if their first chosen color doesn't change.  This is because the result could be neutral or a base/acid.  A good mnemonic tool for remembering which paper is for what is the color it turns--blue is a base.

Let's test something!
Orange juice is good to test for the first time since it has ascorbic acid and changes the litmus paper very quickly.  The blue litmus should turn pink almost instantaneously.  Other acids that you can try are soda pop, vinegar, and surprising to most children, milk.  Milk tends to be mildly acidic.  Tap water in some areas is also mildly acidic, although we didn't get that response in the laboratory in Lake Linden.  For bases, bleach and baking soda mixed with water worked well.  Make sure you include distilled tap water so that you have an example of something neutral.

Safety
Remind children to NEVER mix household chemicals at home, ESPECIALLY acids and bases.  Mixing these two substances can produce violent reactions and release poisonous fumes.
 
 

Shawn Len, 2000.
 
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