Key Concepts
Chemical reaction, thermal decomposition

Introduction

Baking soda is not only great for cooking; it is also a useful chemical for science projects. You have probably heard about and maybe even used the baking soda/vinegar reaction to make volcanos erupt, shoot bottle rockets up in the air, or to detect acids and bases. However, there are many more chemical reactions that you can explore with the help of baking soda. One of them is called a decomposition reaction, which makes baking soda lose weight! Want to find out how it works? Then try this activity!

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

Chemicals can undergo many different reactions such as synthesis reactions that create new substances, or combustion reactions in which a substance usually reacts with oxygen and generates energy in the form of heat. Another reaction type is the decomposition reaction, which is the opposite of a synthesis reaction. When a chemical substance decomposes, it breaks down to form two or more separate compounds. Most chemical compounds are pretty stable and do not decompose spontaneously. You have to put in a lot of energy to break their chemical bonds. However, when chemicals are exposed to enough energy, which can be in the form of heat, radiation, electricity or light, they will decompose.   

Decomposition reactions are the reason why some chemicals or prescription medicines are stored in dark glass bottles. Often times, you do not want a chemical to decompose, as it will change its chemical nature. The dark glass reduces the amount of light that reaches the chemical or medicine, and therefore, prevents light-induced decomposition of the chemical.

Baking soda, or sodium bicarbonate (NaHCO3), is a chemical that can undergo a decomposition reaction when heated. At temperatures above 80°C (176°F), sodium bicarbonate starts to break down into three compounds, forming sodium carbonate (Na2CO3), water (H2O) and carbon dioxide (CO2). You use this reaction every time you cook and bake. The produced carbon dioxide gas makes baked goods rise! The higher the temperature of the sodium bicarbonate, the faster it will decompose. Only sodium carbonate will remain as a solid product. Both carbon dioxide and water are gaseous, which means that they will disappear into the surrounding air. You can actually measure this loss—get some baking soda and find out how, in this activity!  

Materials

  • Heat-resistant plates (2)
  • Spoon
  • Baking soda
  • Digital scale (preferably with 0.1 gram increments)
  • Oven
  • Oven mitts
  • Timer
  • Paper and pen

Preparation

  1. Switch on the scale, zero it, and put the first plate onto the scale. Write down its exact mass.
  2. Then, zero the scale again and add 15 grams of baking soda with a spoon.
  3. Add the mass of the empty plate to the mass of the baking soda to calculate their combined weight. Write down your result on a sheet of paper.
  4. Repeat steps 1–3 with the second plate. Make sure to remember which plate is which. You can label them if you like.
  5. Preheat your kitchen oven to 200°F (about 93°C).

Procedure

  1. Once the oven reaches its target temperature (200°F), place the first plate with baking soda in the oven. Make a note of which one it was.
  2. Set your timer to 15 minutes and leave the plate in the oven until the timer goes off. What do you think will happen to the baking soda in the oven?
  3. Carefully take the plate with the baking soda out of the oven. Make sure to wear oven mitts so you do not burn yourself! How does the baking soda look? Did it change its appearance while being heated?
  4. Set the plate onto your workspace and let it cool for 5–10 minutes.
  5. Then, switch your scale on again, zero it, and set the cooled down plate with the baking soda onto the scale. Write down its exact mass. How does the mass compare to the mass before you put the plate with baking soda into the oven? Did it get heavier, lighter, or stay the same?
  6. Set your oven to 400°F (about 204°C).
  7. When the oven reaches its target temperature, place the second plate with the baking soda inside the oven.
  8. Again, set the timer to 15 minutes and leave the baking soda in the oven the whole time. Do you think you will get a different result at 400°F? What will happen to the baking soda this time?
  9. After 15 minutes, put on your oven mitts and carefully take the plate with the baking soda out of the oven. How does the baking soda look this time? Did it change color or does it still look the same?
  10. Set it aside and let the plate cool down for 5–10 minutes.
  11. Then, switch on the scale again, zero it, and put the second cooled down plate on the scale. Write down its exact mass. How does the mass of the baking soda (plus plate) change while being heated at 400°F for 15 minutes?
  12. Calculate the mass difference of the baking soda before and after the heating at 200°F and 400°F. Subtract the mass of the plate and baking soda after heating from the mass of the plate and baking soda before heating. How much mass was lost or gained during the heating process? Was there a difference between both temperatures?
  13. You can also express the change in baking soda mass by calculating its weight loss in percent (difference of baking soda mass before and after heating [derived in step 12], multiplied by 100, and then divided by the initial baking soda mass [15 grams]. What percentage in mass did the baking soda lose or gain during the heating process at both temperatures? Was it the same? If not, can you explain the difference?

Extra: You can test how the baking soda mass changes at other temperatures. Repeat the same experiment, but set your oven to different temperatures (such as 250, 300, or 350°F). Do you think your results will be different for each temperature, or the same? Why?

Extra: Can you find other substances in your kitchen that can decompose? Find out at what temperatures these compounds decompose at and if possible (and harmless), test it yourself!

Observations and Results

Did you see your baking soda lose weight? You should have—at least for the higher temperature at 400°F. For the lower temperature, your baking soda mass after heating was probably the same (or almost the same) as before you put it in the oven. Baking soda starts to decompose at temperatures around 176°F (80°C). However, at these temperatures, the decomposition will be relatively slow. Fifteen minutes in the oven at 200°F is not enough time to significantly decompose the baking soda.

When you increase the temperature to 400°F, the decomposition reaction will happen much faster. Fifteen minutes is enough time to decompose the baking soda into sodium carbonate, water, and carbon dioxide. The gaseous products (water and carbon dioxide) will escape into the air, which is why your resulting product should be significantly lighter than what you put into the oven.

The appearance of the baking soda will not change at both temperatures. Although you make a new product—sodium carbonate—from baking soda during the decomposition reaction, it will still look the same. Both substances are a white powder.

Cleanup

  1. Let both plates cool down to room temperature. Then, you can dispose of the baking soda in the trash. Wash your hands with warm water and soap and clean your working area.

More to Explore

Credits

Svenja Lohner, PhD, Science Buddies

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Key Concepts
Chemical reaction, thermal decomposition
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