Percent Composition Lab: Chemistry Experiment Using Baking Soda

Percent Composition Lab: Chemistry Experiment Using Baking Soda

Percent composition labs help chemistry students understand how the mass of elements relates to the total mass of a compound. In this hands-on percent composition lab, students determine the percent composition of carbon in sodium bicarbonate by reacting baking soda with sulfuric acid and measuring the carbon dioxide released.

This percent composition chemistry experiment allows students to calculate percent composition experimentally, compare their results to the theoretical value, and determine percent error. It is ideal for high school chemistry students learning percent composition, mass percent, and stoichiometry.

For the extremely busy chemistry teacher, it doesn't get much better than this for a great chemistry lab.

Imagine this:

✔ Quick setup
✔ No crazy materials
✔ Hands-on science
✔ And your students actually having fun while learning percent composition

Sounds like a dream? Nope — it's just good teaching! 😎✨

TL;DR? Find this lab in my TPT store:

• Lab:  Determining Percent Composition

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🧪  Materials for the Percent Composition Lab:

It is a good day for the chemistry teacher when these are the only lab supplies you need. 

• Baking soda 
• 2N sulfuric acid (which equals 1M for sulfuric acid)
• A spot plate
• A Beral pipet (or basically any dropper)
• A laboratory balance
• A test tube

That's it. That’s literally the entire supply list. 🎉

No hunting for exotic lab supplies. No prepping for hours. Just good, clean chemistry (well, mostly clean... there might be a little fizz).

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🌟 What's Happening Here?

Students are going to figure out the percent composition of carbon in baking soda (fancy name: sodium bicarbonate, NaHCO₃). The percentage composition of a compound is the percentage by mass of each of the elements in the compound.  

When you mix baking soda with sulfuric acid, it bubbles and fizzes as carbon dioxide gas is released. According to the Law of Definite Proportions, the mass percentage of carbon in the bicarbonate will be constant, no matter how much sodium bicarbonate is used in the experiment.

Students simply weigh out an amount of baking soda. Drops of 2N sulfuric acid are added to the baking soda, one drop at a time. The reaction releases carbon dioxide. Students continue adding drops of acid until there is no further reaction.  

 

The mass of the apparatus is taken both before and after the completion of the reaction to determine the amount of carbon dioxide that has been released. From the mass of carbon dioxide released, students can mathematically determine the amount of carbon in the released sample, and therefore the percent composition of carbon in sodium hydrogen carbonate.

The student will determine the percent composition of carbon in sodium hydrogen carbonate, both experimentally and theoretically. The student will then determine his/her percent error.

How to Calculate Percent Composition

Percent composition tells you the percentage by mass of each element in a compound.

The formula for percent composition is:

Percent composition = (mass of element ÷ total mass of compound) × 100

In this lab, students determine the mass of carbon indirectly by measuring the mass of carbon dioxide released during the reaction between sodium bicarbonate and sulfuric acid. Using this data, students calculate the percent composition of carbon in sodium bicarbonate and compare their experimental results to the theoretical value. Students learn how to find mass percent using real experimental data, making the concept more meaningful and easier to understand.

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🔥 Why This Percent Composition Lab Works So Well

• Students see the chemistry happening right before their eyes.
• It locks in the concept of percent composition.
• It reinforces the calculations that are being taught in the classroom.
• Supplies are so basic you probably already have them.
• Setup and cleanup are a breeze.
• Real data + theoretical values = perfect chance to teach percent error.
• Safety? Easy. Goggles on, and you're good to go. (Dilute acid = low drama.)

And did I mention? Students LOVE the bubbling. LOVE. IT.

You can find this lab and other related resources in my TPT store:

• Lab: Determining Percent Composition

If you are looking for more easy-to-implement chemistry labs, you may also like this Flame Test Lab, where students observe electron energy levels through color changes.

Flame Tests Chemistry Lab for High School | Flame Test Experiment Guide

Flame tests are a classic high school chemistry lab that allow students to identify metal ions based on characteristic flame colors. In this flame test chemistry lab, students observe how different elements emit distinct colors when heated, helping them connect atomic structure, electron energy levels, and atomic emission to real laboratory observations. This flame test experiment is easy to set up, highly visual, and consistently engaging for high school chemistry students, making it an ideal lab for teaching electron configurations, periodic trends, and the behavior of excited electrons.

This flame test lab is an absolute favorite of mine and a much loved lab by all of my students. The best time to use this lab is when teaching atomic structure, electron configurations, energy levels, ground state, and excited state.  

TLDR? Go straight to my TPT store to view this flame test lab.

What is the purpose of a flame test?

A flame test is used to detect the presence of certain metal ions. The test involves heating a sample of the element and observing the resulting color of the flame. When atoms of elements are heated to high temperatures, some electrons may absorb enough energy to allow them to move to higher energy levels. The element is then said to be in the "excited state." This excited atom is unstable, and the electrons quickly return back to their positions of lower energy or their ground state. As the electrons return to their ground state, the energy that was absorbed is given off in the form of visible light. The color of this light can be used to identify the elements involved. In a flame test, the element will give off a characteristic color that serves as a simple method of identification of that element.   

Purpose of the Lab:

• To observe the characteristic colors produced by metallic ions when heated in a flame.
• To identify an unknown metallic ion by means of its flame test.
• To identify the components of a mixture using cobalt glass.

Required Materials:

Bunsen burner, Lab apron, Wood Splints, Safety goggles, Unknown solutions, Test Tubes, Cobalt glass squares, Test Tube Racks, Nitrate solutions of sodium, potassium, lithium, calcium, strontium, barium, and copper.

Step By Step Procedures, Tips, and Suggestions

• I like to set up different lab stations and have the students rotate through the stations. I set up stations for the 7 different metal ions that I will have the students test. Students are required to rotate through these 7 stations first. The standard flame test procedure helps students identify metal ions based on characteristic flame colors.
• After the students have identified the colors of the above 7 metal ions, I assign an unknown for them to identify.  
• Finally, I have the students use cobalt glass to identify the components of a mixture.

• I have used metal inoculating loops as a means of heating the metal ion sample, but I prefer to use wood splints. They are cheap and disposable. Be sure to soak them in the metal nitrate solutions prior to the start of the lab. 

I set up individual lab stations for each metal ion and have students rotate through the stations. 

In a flame test, the element will give off a characteristic color.  It is difficult to catch on camera, but the photos in this post show the characteristic colors of barium (lime green) and lithium (crimson).

 

After students have observed all colors, I assign them an unknown element to identify. 

Using cobalt glass, students determine the identity of elements in a mixture. 
When viewing the flame test with the naked eye, the student will see the yellow color of sodium.
When viewing the flame test while looking through the cobalt glass the student will see the violet color of potassium.

To me this lab serves a greater purpose than just learning to identify metal ions from their flame tests. This lab gets my students so excited about chemistry.... and that excitement makes all the difference in the world when trying to teach chemistry to high school students.

This lab is in my TpT store and can be viewed at this link.

Flame Test Lab FAQs

What is the purpose of the flame test lab?
The purpose of the flame test lab is to help students identify metal ions based on the characteristic colors they produce when heated in a flame. This lab reinforces the concept of electron excitation and emission while giving students hands-on experience with atomic structure and spectroscopy concepts commonly taught in high school chemistry.

Why is cobalt glass used in a flame test?
Cobalt glass is used in a flame test to filter out the intense yellow light produced by sodium ions. Because sodium is commonly present as a contaminant, its bright emission can mask other flame colors. Looking through cobalt glass helps students more clearly observe the true flame colors of other metal ions.

Other Chemistry Labs Your Students Might Enjoy

If you're looking for additional hands-on chemistry labs for your students, you might also enjoy this percent composition lab, where students use experimental data to determine the composition of a compound.

Another engaging activity students enjoy is this mole concept chemistry lab, which helps students visualize and understand the mole through hands-on investigation.

Students can also explore chemical formulas experimentally in this composition of a hydrate lab, where they determine the water content of a compound using real laboratory data.

Have Fun Teaching!

Chemistry Lab: How Big Is A Mole?

Two facts we all know about teaching chemistry:

• The concept of a "mole" is absolutely crucial to the teaching of our class.
• Many of our students struggle with this concept every single year.

According to the textbook:  A mole is the quantity of a substance that has a mass in grams equal to its molecular mass and contains Avogadro's number of particles.   I think that many students memorize the definition of a mole, but fail to grasp the concept of a mole.  I want my students to be able to visualize a mole and to have a grasp on the size of a mole of substance.

I just added a new lab to my yearly chemistry curriculum.  It is not really an "experiment" but more of a review and reinforcement of the mole concept. The idea of the activity is very simple:  Students are given ordinary household substances and are asked to determine how many moles are in a teaspoon of the substance.

Purpose: 

1. To determine the number of molecules and/or atoms in small amounts of everyday substances.
2. To determine how many moles of chalk it takes to write your name on the board.

Materials:               

• Balance           
• Weighing dishes        
• Plastic spoons
• Water              
• Salt (NaCl)                 
• Sugar (C₁₂H₂₂O₁₁₎
• Chalk              
• Chalkboard    

I had the students find the mass of a teaspoon of a substance.  From this mass, I had students determine the number of moles of substance, the numbers of molecules of substance, and the number of a particular atom within the substance.  The bottom line is that this activity provides repetitive practice in mole conversions.

I was a little concerned that my "sophisticated" high schoolers would find this activity too elementary.  Wrong!!  They embraced the activity whole-heartedly and came away with a better understanding of the "size" of a mole.

The activity concludes with a student-designed experiment.  I asked my students to design an experiment to determine the number of moles of chalk required to write their name on the chalkboard.  Students had to write the steps of their procedure, construct a data table, and convert their data to moles and molecules.  SO SIMPLE, but my students had a great time with this.  They enjoyed comparing the "size" of their name to that of their classmates.

Click above picture to view this product in my TpT store.