This activity gives students experience with chemical change.
- How Stuff Works
Some articles would be good for non-fiction reading for our study
of matter, especially if shortened, including How does bread
work? and How do light sticks work?
- Baking soda
- Calcium Chloride
- Phenol red or other
- Film canisters or small
- Ziploc bags
- The Heat is On! data
- Safety goggles
- Science Experiments You Can Eat, by Vicki Cobb;
- The Science Chef: 100 Fun Food Experiments and Recipes for Kids,
by Joan D'Amico and Karen Eich Drummond;
Background for Teachers
evidence of chemical change that students will see is production of a gas, color
change, and production of heat.
Note: pH is a measure of the acidity or basic nature of a solution.
pH = 7 is neutral; pH < 7 is acid; pH > 7 is base.
The scale is not linear--an acid of pH 4 is ten times more acidic
than a pH of 5.
This activity makes use of pH indicator solution. Indicators show a
change from a base to an acid or an acid to a base. The mixed calcium
chloride, baking soda, and water make an acid solution. Phenol red is the
indicator used in the instructions, but other indicators may be used.
Bromythymol blue works well, changing from a blue to a yellow. Red
cabbage juice (made by boiling the leaves of red cabbage) may be used.
Cabbage juice starts off blue or violet and changes to bright pink. There
are no special safety considerations for any of these indicators.
Calcium chloride is commonly used as a sidewalk ice-melter and
comes in pellets. It is available in the automotive department under the
brand name "Heat" and many others. It is also available through science
supply companies, but is more expensive. When purchased through
science supply companies, it generally comes in small flakes. The
powder from the calcium chloride is harmful if inhaled. The pellet form
is less likely to have powder that can be inhaled. The pellet form is
strongly recommended for safety.
Any time things are mixed or heated in the classroom, safety goggles
must be worn. The amounts of chemicals listed in these instructions are
designed to keep the bags from popping open. Larger amounts of
chemicals produce more gas that may cause bags to pop open and create
an additional splash danger.
Intended Learning Outcomes
1. Use Science Process and Thinking Skills
4. Communicate Effectively Using Science Language and Reasoning
Invitation to Learn
Review the mixing of colors. What does red plus yellow make?
How about blue and yellow? What if you mix red and white? Students
may be surprised when we conduct today's experiment!
- Prepare a Ziploc bag containing two teaspoons baking soda and
one teaspoon calcium chloride for each pair of students. These
amounts should not be increased, or the bag may burst open.
- Prepare small bottles or film canisters (without lids) with
approximately three tablespoons of water. Add two or three drops
of phenol red. Use only enough phenol red to make the color
- Distribute The Heat is On! data sheets and safety
goggles. Read instructions and remind students that goggles must
be worn until the chemicals are disposed of and desks are clean.
- Discuss what makes a good scientific observation. Measurements
are great! Objective observations are great! Statements like "it
stinks" or "it turned an ugly color" are opinions and could be
rephrased to be more objective. Saying, "It has a strong odor," or
saying, "It changed to a bright yellow-orange color," is more
- Goggles should be worn at this point. Distribute bags and bottles.
- Make initial observations about contents of the bag and bottle.
Students record observations on the data sheet. Remember to
- Zip the bottle inside the bag.
- Tip bottle over and observe. Remember to measure temperature.
- Record observations on data sheet.
- Clean up by placing closed bags into garbage. Wash hands and
put away goggles.
- Discuss the evidence of chemical change. Students may write a
one paragraph summary of the activity.
- Students write a paragraph telling what they know about chemical
change, giving examples from this activity and daily life.
- Allow students to illustrate what they observed in the activity
without writing the sentences OR just label the things that are
evidence of chemical change like “heat,” “color change,” “new
gas.” Students may record some observations in drawing form
- Pair ELL students with a partner with the same primary language
to do the writing work.
- Review key vocabulary words before beginning writing.
- Most students know what happens when they mix baking soda
and vinegar together—it bubbles indicating that a gas has formed.
With adult supervision, try other cooking liquids (e.g., milk,
buttermilk, lemon juice, orange juice, etc.) to find which form a
gas when combined with baking soda.
- Students make a T-chart listing the physical and chemical changes
involved in preparing a favorite food.
- Assess student learning using the “filmstrip” at the bottom of the
data sheet. Did s/he identify evidence of chemical change?
- Students write a paragraph explaining how they know something
has undergone a chemical change.