Vanishing Baking Soda

Key concepts
Chemistry
Gases
Chemical reaction
Thermal decomposition

Introduction
Baking soda is not only great for cooking, but 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 homemade volcanoes erupt, shoot bottle rockets up in the air or to detect acids and bases. There are many more chemical reactions, however, 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?

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. When chemicals are exposed to enough energy, which can be in the form of heat, radiation, electricity or light, they will decompose, however.

Decomposition reactions are the reason why some chemicals or prescription medicines are stored in dark glass bottles. Oftentimes, you do not want a chemical to decompose, because its chemical nature will change. 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 176 degrees Fahrenheit (80 degrees Celsius), 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 at the warm temperature, 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

• Two oven-safe plates
• Spoon
• Baking soda
• Digital scale (preferably with 0.1-gram increments)
• Oven
• Oven mitts
• Adult helper
• Heat-safe surface
• Timer
• Paper and pen or pencil
   

Preparation

• Preheat your kitchen oven to 200 degrees F (about 93 degrees C).
• Switch on the scale and zero it.
• Put the first plate onto the scale. Write down its exact mass.
• Then zero the scale again and add 15 grams of baking soda with a spoon.
• 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.
• Repeat these steps with the second plate. Make sure to remember which plate is which. You can label them if you like.
   

Procedure

• Once the oven reaches its target temperature (200 degrees F), have your adult helper place the first plate with baking soda in the oven. Make a note of which one it was.
• 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?
• Have your adult helper carefully take the plate with the baking soda out of the oven. Make sure to wear oven mitts! How does the baking soda look? Did it change its appearance while being heated?
• Set the plate onto your workspace's heat-safe surface, and let it cool for five to 10 minutes.
• Set your oven to 400 degrees F (about 204 degrees C).
• 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 with the mass before you put the plate with baking soda into the oven? Did it get heavier, lighter or stay the same?
• When the oven reaches its new target temperature, have your adult helper place the second plate with the baking soda inside.
• 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 degrees F? What will happen to the baking soda this time?
• After 15 minutes have your adult helper use oven mitts to 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?
• Set it aside and let the plate cool down for five to 10 minutes.
• 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 degrees F for 15 minutes?
• Calculate the mass difference of the baking soda before and after the heating at 200 degrees and 400 degrees 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?
• You can also express the change in baking soda mass by calculating its weight loss as a percentage (the difference of baking soda mass before and after heating, multiplied by 100 and then divided by the initial baking soda mass). 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 test but set your oven to different temperatures (such as 250, 300 or 350 degrees 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 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 degrees 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 degrees F. At these temperatures, however, the decomposition will be relatively slow. Fifteen minutes in the oven at 200 degrees F is not enough time to significantly decompose the baking soda.

When you increase the temperature to 400 degrees 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 either temperature. 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
Be sure to turn off the oven. Let both plates cool to room temperature. Then you can dispose of the used baking soda in the trash. Wash your hands with warm water and soap, and clean your working area.

More to explore
Thermal Decomposition, from BBC Bitesize
Chemistry for Kids, Chemical Reactions, from Ducksters Education Site
Equation for the Decomposition of Sodium Bicarbonate, or Baking Soda, from ThoughtCo.

This activity brought to you in partnership with Science Buddies