What to do
MIX one tasting solution in each cup. LABEL the cups with appropiate letters, such as "B" for baking soda or "V" for vinegar. PLACE the cups in front of the class.
DRAW 4 pictures of a tongue on the board. TELL the students they will use their tongues to make a taste map. WARN students that they should never taste unknown solutions. In this activity the solutions are safe, but some acids and bases can cause injury if ingested.
BLINDFOLD a student. ASK that student to hold his nose. DIP a cotton swab into a solution and lightly TOUCH it to various areas on the student's tongue. Ask him to WRITE a letter on the tongue diagram to show where he tasted the solution the most, such as a "B" for baking soda, a "V" for vinegar, an "L" for lemon juice and a "C" for cocoa.
DIVIDE the class into pairs. Have each pair TEST the solutions on different parts of their tongues, and LABEL a tongue diagram for each taste. Be sure to use a new swab each time. ASK students if some parts of their tongues are more sensitive a particular taste than others.
What's happening? Find out more about tasting acids and bases.
Challenge. What other foods that we eat have a bitter or sour taste? Why is it important for the tongue to taste sour and bitter? Share your results in the pH Exchange.
Magic Liquids: Can one solution change color when added to other solutions?