Chemistry in a Ziploc Bag HS

Purpose: Using evidence, identify physical and chemical changes.

Research: Analyze the procedure below and identify every instance where different substances come in contact. Using the notes page and other resources available to you, predict if this contact will produce a physical or chemical change. Research and indicate the specific evidence you will be looking for in your observations that will support your prediction (How will you know it’s a physical or chemical change?). (Hint: There are 4 times when different substances come in contact.)

Predictions of What Happens When Substances Make Contact

Items Coming in ContactPhy or ChemEvidence expected

1.

2.

3.

4.

Experiment:

Create a data table to collect your observations to help you determine if your predictions above were supported or refuted.

Procedure

•Place 1 spoon of CaCl2 (calcium chloride) in the right corner of a quart or gallon ZipLock bag.

•Place 1 spoon of NaHCO3 (baking soda) into a film canister and add 20 mL of water and set aside.

•Put 20 drops of indicator (Bromothymol Blue) into 20 ml of water and swirl to mix.

•Pour the water and Bromo. Blue into the Ziploc bag and gently swirl the bag.

•Carefully, place the film canister with the water and baking soda into the ZipLock bag without spilling any into the bag.

•Carefully push as much air as possible out of the bag and seal the bag.

•Tip the film canister over and dump the contents into the bag.

•Hold the bag away from any faces

•Gently rock the bag back and forth to mix the contents in the bottom while gently massaging the corners to improve the mixing and to feel for any possible changes.

•Record all observations in an organized, easy to read format.

Observations

Analysis Questions:

  1. Which substances coming into contact caused physical changes? What is the evidence for each of them that supports your claim it was a physical change?
  1. Which substances coming into contact caused chemical changes? What is the evidence for each of them that supports your claim it was a chemical change?
  1. There are a number of piece(s) of evidence that indicate a chemical change has occurred. Were there any pieces of evidence you found in your reading/research that were not present at all in this experiment? If so, what were they
  1. Was there evidence that any additional chemical changes occurred that you did not predict? If so, when did it occur and what was the evidence?
  1. What would happen if CaCl2 was not present in the experiment?