In this lab students will observe an endothermic chemical reaction involving baking soda (sodium bicarbonate) and vinegar (acetic acid). Students will investigate the signs a chemical reaction has occurred (gas production, change in temperature). Students will perform the lab in an open system so they can see the change of mass due to gas production. This lab is a lead into the topic of conservation of mass. After the lab is completed, the teacher should do a demonstration of the exothermic reaction Hydrogen peroxide and potassium iodide.
High or middle school
By the end of this lab, students should be able to
- Observe, identify, and describe signs of a chemical reaction
- Calculate the mass before and after a reaction
- Use the Law of the Conservation of Mass to determine why the mass before the reaction was different than the mass after the reaction
- Differentiate between endothermic and exothermic reactions
This lab supports students’ understanding of
- Chemical Reactions
- Conservation of Mass
- Endothermic Reactions
- Exothermic Reactions
Teacher Preparation: 30 minutes
Lesson: One-two 90 minute class periods or two-three 50 minutes class periods
- Acetic Acid (vinegar, 50 ml for each group)
- Sodium bicarbonate (baking soda, 1 tablespoon for each group)
- 50 ml to 100 ml graduated cylinders (1 for each group plus one for demo)
- 400 ml beaker (1 for each group plus one for demo)
- balance (1 beam balance or 1 electronic balance for each group)
- thermometer ( 1 for each group plus demo)
- hydrogen peroxide (50 mL) teacher use only
- potassium iodide ( 1 teaspoon) for teacher use only
- weighing paper
- Always wear safety goggles when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
- When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
- Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
- When baking soda and vinegar are mixed together, an endothermic chemical reaction occurs. Gas is produced and observed as bubbles. The temperature decreases. If the experiment is performed in an open system, the final mass will be less than the initial mass. This is because a gas is produced during the reaction. The discrepancy in mass is due to the gas escaping the system. If the experiment were to be performed in a closed system then the final mass would the same as the starting mass (ignoring human error). When hydrogen peroxide and potassium iodide are mixed together an exothermic chemical reaction occurs. Gas is produced and energy is released in the form of heat.
- Teacher should set up the lab stations for the lab groups.
- Students should be in groups of 3 to 4 students.
- The teacher will have the potassium iodide and hydrogen peroxide demo set up in a central location for the students to observe.
- Students will need to be introduced to the concepts of chemical changes, signs of chemical changes, and the Law of Conservation of Mass.
- Prior to starting the lab, the teacher should go over the “problem” questions with the students.
- In the pre-lab questions students are asked to find the chemical formulas for acetic acid and sodium bicarbonate. At this point in the class students are not yet able to write a balanced equation. The purpose of this is to introduce them to chemical formulas.
- Students should notice bubble formation which indicates gas formation in a chemical reaction.
- Because the experiment is performed in an open system, teacher should explain how the mass lost after the reaction was due to the gas escaping the system.
- For a more advanced lab students could perform the exothermic reaction themselves
- The demo should be performed before students perform their own experiments
- The teacher should measure 50 mL of hydrogen peroxide in a graduated cylinder then pour it into a 400 mL beaker and record the mass.
- Once the peroxide is in the beaker, the teacher should measure the temperature with a thermometer.
- The teacher should then mass 1 teaspoon of potassium iodide and add it to the hydrogen peroxide beaker.
- Students should be observing the chemical reaction taking place: bubble formation, change of color, heat production
- For a longer lab, students can perform the same endothermic reaction in a closed system to observe how the mass of the product is the same as the starting mass of the reaction.
For the Student
A chemical reaction occurs when bonds between atoms are broken and new bonds are formed. When a chemical reaction takes place, there are usually signs. Some common indicators a chemical reaction has taken place are: change in color, an odor forming, light formation, sound, bubbles, and/or a change in temperature. During a chemical reaction, matter is neither created nor destroyed, it is conserved. Chemical reactions occur everyday. Some of the most common chemical reactions we encounter occur in the kitchen when we cook or bake. A common household cleaner than you can make at home involves chemically reacting vinegar and baking soda.
- Define Law of conservation of mass:
- Define Endothermic:
- Define Exothermic:
- What is the chemical name and formula for vinegar?
- What is the chemical name and formula for baking soda?
- Write a hypothesis describing what you think will happen if baking soda and vinegar are mixed together in terms of chemical or physical reactions:
- Safety goggles (each person)
- Acetic Acid: 50 ml
- Sodium bicarbonate: 1 tablespoon
- Weighing paper
- 50 ml graduated cylinder
- 400 ml beaker
- Always wear safety goggles when handling chemicals in the lab.
- Wash your hands thoroughly before leaving the lab.
- Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
- When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
- Wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
- Gather materials at lab table.
- Mass the 400ml empty beaker and record mass in your data table.
- Obtain 50ml of vinegar with the graduated cylinder and add to beaker.
- Mass the beaker with the vinegar and record the results in your data table.
- Subtract values to calculate the mass of only the vinegar and record its mass in your data table.
- Obtain a weighing paper.
- Determine the mass of 1 tablespoon of baking soda and record in your data table.
- Using the thermometer, determine the starting temperature of the vinegar and record in your data table.
- After recording all the masses prior to the experiment, add the baking soda to the vinegar in the beaker.
- Record all observations in your data table, such as:
- Temperature change
- After the experiment has concluded, collect the mass the beaker with all of its contents again and record the results in your data table.
- Collect the final temperature of the contents in the beaker if you have not already, record it in your data table.
- When the data table is complete, pour the contents of your beaker down the sink with running water.
|Mass of empty beaker|
Starting mass of beaker and vinegar
Starting mass of vinegar only
Mass of baking soda (and filter paper)
Starting temperature of Vinegar
Total mass of beaker and baking soda before the reaction (without beaker)
Observations of Chemical Reaction
|Total Mass of system after reaction (without beaker)|
- What was the starting mass of your experiment?
- What was the final mass of your experiment?
- Using your starting mass and final mass, calculate the mass lost due to gas production:
- Using the Law of Conservation of Mass, compare your starting mass and final mass. Why do you think that your starting mass and ending mass were different?
- How could the experiment been performed differently to achieve an ending mass that was more accurate to the starting mass?
- Acetic acid and sodium bicarbonate are two commonly found household chemicals that undergo a chemical reaction when combined. Why do you think it is important to know which chemicals form chemical reactions at home?
- What are some other chemical reactions you can notice around your house?
- Was this reaction endothermic or exothermic? How do you know?
- Was the demo lab exothermic or endothermic? How do you know?
- How can an exothermic reaction be beneficial to society?
- Investigate the use of coal combustion and explain if the use of fossil fuels is considered as exothermic reactions.