Lesson 1.2 - Starting Point Activity

A student performed the investigation on page 5 in the textbook and recorded the following observations:

                   

Read the above observations; then, answer the following questions.

Question 1. Why was the phenol red and water put into a film canister and sealed before it was put into the plastic bag?

Question 2. Why were the calcium chloride and sodium bicarbonate not kept separate?  If you read step 1 in the "what to do", the instruction is to place the two chemicals in the plastic bag.

Question 3. Why was this chemical reaction kept inside a sealed plastic bag?

Question 4. What were the observed colour changes?  How would you explain the changes in colour?

Question 5. What other changes were recorded by the student?

Then, return here to continue this lesson.

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. Why was the phenol red and water put into a film canister and sealed before putting it into the plastic bag?

The phenol red and water had to be kept in a film canister to prevent any reaction with the other chemicals until the plastic bag was sealed.

Question 2. Why were the calcium chloride and sodium bicarbonate not kept separate?  If you read step 1 in the "what to do" the instruction is to place the two chemicals in the plastic bag.

The calcium chloride and sodium bicarbonate are solid chemicals that will not react unless they are first mixed with water.

Question 3. Why was this chemical reaction kept inside a sealed plastic bag?

This chemical reaction was kept inside a sealed plastic bag because a gas was produced that could have been dangerous.  Also, the reaction was foaming and bubbling, which could have made a mess if not contained in the plastic bag.

Question 4. What were the observed colour changes?  How would you explain the changes in colour?

The observations in the table indicate the white powders and the red liquid changed to a yellow mixture.  The colour changes are the result of a chemical reaction that produced new substances. 

Note:  You should know more about this reaction.  The phenol red indicator turns yellow in the presence of an acid, so an acid must have been produced in the chemical reaction.  Because an acid was produced, the reaction should have been confined in a plastic bag.

Question 5. What other changes were recorded by the student?

The student recorded that the temperature increased and the bag expanded.  This indicates that the chemical reaction produced heat and at least one gas.


Go to the next page to learn more about chemicals around you.