Problem: How do we know a chemical reaction has occurred, and how do we know when a physical change has occurred?

Materials:

  • 1 spoon each of sodium bicarbonate NaHCO3 and calcium chloride CaCl2
  • water, graduated cylinder or beaker
  • Bromothymol Blue
  • 1 Ziploc bag
  • Goggles

What do we know?

What is a physical change?

What is a chemical change?

How do we know that a physical change has occurred?

How do we know that a chemical change has occurred?

(Record what you already know based on: pages 388-391 in your text,previous activities in this unit.)

What do we need to know?

What is BromothymolBlue?

What are the chemical properties of NaHCO3? (What does it react with and what is the evidence?)

What are the chemical properties of CaCl2? (What does it react with and what is the evidence?)

How do I present my solution?

I will submit a lab report including the following :

  1. Statement of problem
  2. Explanation of : “What do we know?” (respond to questions above)
  3. Explanation of : “What do we need to know?” (respond to question above)
  4. Completed data table
  5. Response to analysis questions.

Safety Precautions: wear goggles, no tasting, no smelling, no horseplay

Create the following table.

Substance / PP / CP / Substance mixed with water & Bromothymol Blue / Physical change?
Yes or No
evidence / Chemical change?
Yes or No
evidence / Substance #1 with water & blue combined with substance #2 with water & blue / Physical change?
Yes or No
evidence / Chemical change?
Yes or No
evidence
#1 NaHCO3 (baking soda)
#2 CaCl2
(calcium chloride)
#3 Water
#4 Bromothymol blue

Procedure:

  • Part 1: Put 5-8 drops of Bromothymol Blue in your beaker of water and mix by swirling it around.
  • Place 1 spoon of NaHCO3 (baking soda) one canister fill the container 2/3-3/4 full with the blue water. Snap the lid on and gently shake to mix.
  • Carefully observe and fill in the observation chart.
  • Part 2: 1 spoon of CaCl2 (calcium chloride) in the other canister and fill 2/3-3/4 full with the blue water. Snap the lid on and gently shake to mix.
  • Carefully observe and fill in the observation chart.
  • Part 3: Pour the NaHCO3 (baking soda) into the ziplock bag
  • QUICKLY pour the CaCl2 (calcium chloride) in the ziplock bag and ZIP it IMMEDIATELY AND COMPLETELY.
  • Carefully observe and fill in the observation chart.
  • Hold bag away from any faces

Analysis Questions:

  1. Was the change in Part 1 physical or chemical? What is your evidence?
  1. Was the change in Part 2 physical or chemical? What is your evidence?
  1. Was the change in Part 3 physical or chemical? What is your evidence?
  1. What was the most convincing evidence showing the occurrence of a chemical change? Explain why you selected this evidence.