(glue into science journal when instructed to)
Name: _________________________ Per: ____
Lab: Exothermic or Endothermic?
Introduction: In the presence of water, citric acid [C6H8O7] and sodium bicarbonate [NaHCO3] (also
known as baking soda) react to form trisodium citrate [Na3C6H5O7], water [H2O] and
carbon dioxide [CO2].
C6H8O7 + 3NaHCO3  Na3C6H5O7 + 3H2O + 3CO2
citric acid + sodium bicarbonate trisodium citrate + 3 water + 3 carbon dioxide
Purpose:
Materials:
To decide whether a chemical reaction is endothermic or exothermic.
sodium bicarbonate (NaHCO3) solution, citric acid solution, digital scale, thermometer,
pipettes, test tubes, test tube rack, spill tray, calcium chloride (CaCl2) solid, spoon.
Procedure:
PART A
1. Assemble apparatus as shown by teacher. (The test tube is in the rack with the thermometer
inside the proper test tube.)
2. With pipette, measure about 3 mL of NaHCO3 solution (blue) Don’t mix up the pipettes!
3. Add this into test tube A. Record temperature reading to one decimal place.
4. With other pipette, measure about 3 mL of citric acid solution (yellow).
5. Carefully combine the two liquids into test tube A.
6. Do not stir with the thermometer!
7. Watch the chemical reaction and contain any spills by keeping the test tube rack on the tray.
8. Record your observations in your data table. Rinse your thermometer in the sink.
PART B
1. With pipette, measure about 3 mL of citric acid solution (yellow).
2. Add this into test tube B. Record temperature reading to one decimal place.
3. Measure 0.5 grams of calcium chloride (CaCl2) onto the transfer paper on the digital scale.
4. Carefully add the solid CaCl2 from the transfer paper into test tube B. Return paper to scale.
5. Do not stir with the thermometer! (It is ok if some solid is stuck to the sides.)
6. Watch the chemical reaction and contain any spills by keeping the test tube rack on the tray.
7. Record your observations in your data table.
PART C
1. After all observations have been written down, begin cleaning up your station.
2. Empty and rinse all test tubes thoroughly in the sink
3. Rinse the thermometer and the tray in the sink.
4. Dry the tray, test tube rack, and the outside of test tubes
5. Compare your table to the picture on the board. Your table should be similar!
Pre-lab questions:
1) What are the reactants in the above reaction? _________________________________________
2) What are the products in the above reaction? __________________________________________
3) Describe what you will do with the solid CaCl2 :
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
When your group is finished with the pre-lab questions, you must get the questions checked
by Mr. Woodward before you begin the lab.
DATA TABLE: (glue into science journal when instructed to)
Physical Properties (describe its appearance)
NaHCO3 solution
Citric Acid solution
Calcium Chloride (CaCl2)
solid
RECORD OBSERVATIONS
Before Reaction
Test Tube A
blue liquid with white
solid at bottom
Test Tube B
yellow, transparent
liquid
Before Reaction (°C)
During & After Reaction
At End of Reaction (°C)
Test Tube A
Temperature
Test Tube B
Temperature
Post-Lab Questions:
1) Think of the 5 signs of a chemical reaction. Identify all of the signs that you observed in this
chemical reaction? ______________________________________________________________
_____________________________________________________________________________
2) Explain what type of reaction occurred in test tube A? Be sure to use these terms in your
explanation: exothermic or endothermic, temperature, and heat energy.)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
3) Explain what type of reaction occurred in test tube B? Be sure to use these terms in your
explanation: exothermic or endothermic, temperature, and heat energy.)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
4) Identify the gas that was formed in this reaction? (Hint: look at the written reaction)
The gas produced was: _______
5) Count how many of each atom are in the reactants and products.
C6H8O7 + 3NaHCO3  Na3C6H5O7 + 3H2O + 3CO2
Reactants
Products
C= ____ H= ____
C= ____ H= ____
O= ____ Na= ____
O= ____ Na= ____