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 Mole Lab Activity: How Big Is a Mole?

The mole concept is one of the most important topics in a chemistry course, but it is also one of the most difficult for students to truly understand.

Students can memorize definitions and formulas, yet many still struggle to visualize the size of a mole or understand how mole conversions connect mass, atoms, and molecules. Because of this, students benefit from hands-on activities that allow them to measure substances and perform real calculations.

One activity that works particularly well is a simple lab where students determine how many moles are present in a teaspoon of common substances.

This lab is quick to set up, uses inexpensive materials, and gives students meaningful practice converting between mass, moles, and molecules.

Simple Materials for This Mole Lab

One of the things I love most about this activity is how easy it is to prepare. The materials are simple and inexpensive, and most chemistry classrooms already have everything needed.

Materials include:

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

Because the materials are so simple, this lab works well as:

• An introduction to the mole concept
• A practice activity during a mole unit
• A review before moving into stoichiometry

Teachers can quickly set up stations by placing the materials at lab tables and distributing the student lab pages.

What Students Do in the Activity

Students begin by determining the mass of one teaspoon of a substance such as water, salt, or sugar.

After measuring the mass, students perform a series of calculations to determine:

• The number of moles in the sample
• The number of molecules present
• The number of atoms of a specific element within the compound

This process gives students repeated practice converting between:

mass → moles → molecules

Because students are working with real measurements rather than abstract numbers, they begin to develop a much better sense of how chemists use the mole as a counting unit.

Student Designed Investigation

The second part of the activity adds an inquiry component.

Students design their own simple experiment to determine how many moles of chalk are required to write their name on the chalkboard.

Students must:

• Describe their experimental procedure
• Construct a data table
• Collect measurements
• Convert their data into moles

This portion of the lab gives students additional practice with:

• The scientific method
• Experimental design
• Mole conversions

Students also enjoy comparing the size of their names and discussing their results with classmates.

Why This Lab Works Well in the Classroom

Many students struggle with the mole concept because it feels abstract and disconnected from real substances.

This activity helps students see how mole calculations relate to actual measurements. By working with familiar materials such as water, salt, and sugar, students begin to understand how chemists connect mass and the number of particles in a sample.

The lab also works well because it combines:

• Hands-on measurement
• Calculation practice
• Student-designed investigation

Together, these elements reinforce the mole concept in a way that lectures and worksheets alone often cannot.

Use This Mole Concept Lab in Your Classroom

If you would like to use this activity with your students, you can find the complete lab here.

The resource includes:

• Student lab pages
• A complete teacher guide
• Answer key
• Instructions for the student-designed chalk investigation

This activity works well for Physical Science or Chemistry students in grades 9-12 and is easy to set up for classroom use.

More Chemistry Labs for Your Classroom

If you are looking for additional chemistry labs, you may also enjoy reading about these activities:

Percent Composition Lab

Flame Tests Chemistry Lab

For another activity that helps students understand the mole concept, be sure to read:

Making the Mole Concept Click and Stick Lab

Final Thoughts

The mole is one of the foundational ideas in chemistry, but students often need multiple experiences working with real substances before the concept truly clicks.

This simple lab provides students with an opportunity to measure, calculate, and apply mole conversions in a meaningful way. With inexpensive materials and minimal preparation, it is an easy activity to add to any mole unit.