Name: ______Date: ______Core: ______

Endothermic-Exothermic Lab: Part 1

CHALLENGE: Determine what part of a chemical reaction is endothermic and what part is exothermic.

BACKGROUND INFORMATION:

In this experiment you will mix several chemicals, make observations of the reaction, and then later use experimentation to determine which part of the reaction is responsible for each observation you made.

The chemicals involved are calcium chloride, sodium bicarbonate (baking soda), and phenol (pronounced “fee-nawl”) red. Below are the chemical formulas for each. Figure out how many atoms are in each molecule and the types of bonds involved:

a.  Calcium Chloride (CaCl2)

Number of atoms per molecule: Calcium______Chlorine ______

Calcium Chloride is an ______bond.

b.  Sodium Bicarbonate (NaHCO3)

Number of atoms per molecule: Sodium_____ Hydrogen_____ Carbon_____ Oxygen____

Baking soda has both ______and ______bond.

c.  Phenol Red (C19H13O5S) dissolved within a solution of water (H2O).

Number of atoms per molecule: Sulfur_____ Hydrogen______Carbon______Oxygen_____

Phenol Red has ______bonds between the atoms.

PART 1: INITIAL REACTION OBSERVATIONS

PROCEDURE:

1.  Put 1 teaspoon of sodium bicarbonate into the correctly labeled cup.

2.  Put 3 teaspoons of calcium chloride into a correctly labeled cup.

3.  Measure out 10 ml of phenol red and put it into an unlabeled paper cup.

Make observations for the reactants of each material:

Calcium Chloride: / Sodium Bicarbonate: / Phenol Red:

PROCEDURE CONTINUED:

1.  Pour the baking soda and calcium chloride into the same ziplock bag. We are reusing these cups, please do not damage them.

2.  Seal the bag. Place the bag and the cup of phenol red onto the scale. Record the mass on your data sheet below. Place the thermometer on the outside of the bag. Record the temperature below.

3.  Take the bag off the scale. Open the bag. Put the cup into the bag standing upright. Remove excess air. Make sure the bag is well sealed.

4.  Tip the cup of phenol red solution into the bag contents and knead the bag several times to mix.

5.  Find the mass of the bag after mixing it and before you open it up. WARNING: If it seems the bag is going to explode open, hold the bag away from your face and open it at the top to release the gas.

6.  After finding the mass, place the thermometer on the outside of the bag and find the temperature. Record below.

7.  With the bag facing away from you, open the bag to let the gas out. Record the mass of the bag after it has been opened.

Observations:

Qualitative Quantitative

Explain in detail chemical changes you observed: / Mass before mixing ingredients: 28.6 g
Temperature before mixing: 22 degrees C
Mass after mixing: 8.6 g
Mass after opening: 8.3 g
Mass of escaped gas: 20.3 g
Temperature After Mixing: 32 degrees C
QUESTIONS
o  Why did it become warm?
o  What causes the bubbles?
o  What caused the color to turn yellow, pink, orange, green(?)
o  Why were some places colder than others?

REFLECTION

During the initial chemical reaction you explored, there is an endothermic reaction and an exothermic reaction (maybe you noticed both). Which reaction (endothermic or exothermic) had a greater transfer of energy involved? How do you know?

Exothermic had the greater transfer of energy because the temperature increased 12.1 degrees C.

What evidence exists that a new substance is formed during the reaction?

The bag was sealed, but at the end the bag filled with air. This suggests that a gas was formed. When opened, the bag was 1.4 grams less than before.

State the evidence from the experiment that supports this claim: When a chemical reaction occurs, matter is not created or destroyed in the process, therefore mass is conserved.

The mass before and after the mixture should have stayed the same. Some might have less mass due to gas escaping the bag.

In the reaction, calcium chloride and baking soda reacted to produce calcium carbonate, sodium chloride, water, and carbon dioxide. Use what you know from the background information section on the first page as well as the periodic table to create a chemical equation modeling this reaction:

CaCl2 + NaHCO3 + C19H13O5S + H2O

Endothermic-Exothermic Lab: Part 2

Your job now is to determine which part of the reaction is responsible for these different observations. As you experiment, fill out the table on the next page. When mixing chemicals reuse the same bag, rinsing it out each time and do not use more than the amounts stated in the first procedure. Summarize results below:

Exothermic reaction: CaCl2 + H2O

Endothermic reaction: NaHCO3 + H2O

Color change reaction: C19H13O5S + NaHCO3

Gas forming reaction: CaCl2 + NaHCO3 + H2O

Check the boxes for the two or three chemicals you mixed: