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This activity gives students experience with chemical change.
The 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 linearan 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.
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 todays experiment!