Getting Down to Basics (and Acidics)

Deborah Lewis                  Hinton School
                               644 West 71St. Street  
                               Chicago, Il. 60621
                               312-962-9176

Objectives:

Grade level 7th
1. Students will identify and define the concepts of acid, base, indicator and 
   neutralization.  
2. Students will identify, classify and observe common household substances as 
   an acid, a base or neither. 
3. Students will record all observations and findings in a data table. 

Materials Needed:

dilute hydrochloric acid             bleach          orange juice     
dilute sodium hydroxide solution     soda water      scouring powder
red litmus paper                     corn syrup      tea
blue litmus paper                    limewater       baking soda
beakers or small glass jars          alcohol         milk
household ammonia                    table salt      lemon juice 
milk of magnesia                     detergent       seltzer tablet
goggles                              labels          phenolphthalein

Recommended Strategies:

The words acid, base, indicator and neutralization will be developed.  Teacher 
will pass out to students pieces of lemons.  Students will use their sense of 
taste and taste the lemon.  They will conclude that an acid is a chemical 
compound that tastes sour.  Next a bar of soap (which has been left in water) 
will be, passed out to students (use sense of touch).  One student will be 
selected to sip some black coffee (sense of taste).  They will conclude that a 
base is a chemical compound which is slippery and taste bitter.  For all 
practical purposes you should never touch or taste an acid or base.  Acids and 
bases, which are strong, can be poisonous and corrosive to skin.  To taste or 
touch are not safe methods to identify an acid or base. 
 
Teacher will do a demonstration on "Turning Water to Wine" by the following 
method:  Place 20ml of a base into one beaker, and 20ml of an acid into a second 
beaker.  Pour water that contains phenolphthalein, a colorless indicator into 
the first beaker.  The water appears to change into a red wine (or pink).  Pour 
red solution into the second beaker and it appears to turn back into water.  Do 
not discuss at this point. 

Students will be asked a question.  Suppose you are driving a car and your gas 
is low.  When the needle reaches past the red mark, what happens?  (low fuel) 
What is the device called that monitors the low fuel?  (low fuel indicator 
light)  From the demonstration and the question, students should elicit the 
definition of indicator as a substance that changes colors when acids and bases 
are present.  That neutralization is when an acid and base combine, they react 
in a neutralization reaction.  The products of a neutralization reactions are 
water and salt. 

EXPERIMENT:  
             PART 1
Demonstration:  
1. Put a small amount of dilute hydrochloric acid in one beaker and a small 
   amount of sodium hydroxide solution, a base, in another.  CAUTION: use care in 
   handling acids and bases.  
2. Dip a piece of red litmus and blue litmus paper into each beaker.  Observe 
   which piece of litmus paper changes color in each liquid.  Record your 
   observation. 

Use your observations to answer the following questions.
1. Which piece of litmus paper change color in the dilute hydrochloric acid?
2. Which piece of litmus paper changed color in the dilute sodium hydroxide 
   solution?
3. How can red litmus paper and blue litmus paper be used to tell whether a 
   substance is an acid, a base, neither?

             PART 2
Directions:  In this part of the activity you will test some common household   
substances to find out if they are acids, bases, or neither.  You may share the
materials with other students' but you should make and record your own 
observations.
1. Put small amounts of the substances to be tested in small beakers.  Add water 
   to the beakers containing solid substances.  Label each beaker with the name of 
   the substance it contains.  
2. Dip a piece of red litmus paper and a piece of blue litmus paper into each 
   substance.  Those substances that change the color of the litmus the way 
   hydrochloric acid does are acids.  Those that change the color of the litmus 
   paper the way the sodium hydroxide does are bases.  Those that do not change 
   the color of either red or blue litmus paper are neither acids nor bases.  
   Record your observations in the table.    
  
Use your data and observations to answer the following questions
1. Which of the substances that you tested caused blue litmus paper to turn 
   red?
2. To what class of compounds do the substances that caused the paper to turn 
   red belong?  How do you know? 
3. Which substances that you tested caused red litmus paper to turn blue?
4. To what class of compounds do the substances that caused the paper to turn 
   blue belong?  How do you know?
5. Which of the substances that you tested did not change the color of either
   blue litmus paper?
6. To what class or classes of compounds might those substances that did not 
   change the color of either red or blue litmus paper belong?
7. How do the results of this activity compare with your expected outcome?