The Business of Fizziness: Test Your Soda Fizz!

Introduction

You’ve probably seen the reaction that happens when you add Mentos candy to a diet soda. The resulting eruption is powerful enough to be dangerous, and is the source of many online videos! While many people are familiar with this reaction, few of them understand why it takes place. The Mentos + Soda reaction is not actually a chemical one, but a physical one called ‘nucleation’. In this activity we will explore nucleation in soda at a smaller scale by adding some unusual ingredients to our soda!

Background

Carbonated drinks like soda are in a state of super saturation, meaning soda is completely saturated with CO2 and can’t hold anymore. Once any solution is saturated, it generally won’t contain any more of the saturating substance. For example, if you add sugar continuously to a glass of water, eventually you'll reach a point where the sugar just sinks to the bottom of the glass instead of dissolving in the water.

However, if you heat the solution of sugar and water, the water will be able to accept more of the sugar than it could when the water was cool or room temperature. Once the heated water has cooled to room temperature, it will be super saturated with sugar – more sugar will be dissolved in the water than would normally be possible at room temperature.

CO2 is added to water to make soda in a similar manner. The water has been super-saturated with CO2, and then bottled and sealed to keep the CO2 dissolved in the soda. The CO2 is always trying to escape from the soda, and as a result once the soda bottle is open you see small bubbles forming and drifting to the top.

Materials

Procedure

Observations and Results

In this activity you added different kitchen compounds to soda, and observed the reaction. You should have noticed that the when you added salt and sugar, the soda ‘fizzed’, with lots of bubbles rising to the surface of the drink. You should have noticed both the sight and sound of the gas leaving, as well as fewer bubbles in the soda when you tasted it. In contrast, adding the oil had little effect on the bubbles in the soda. The reason for this has to do with how the gas in soda - carbon dioxide (CO2) – get into soda, and how it behaves once it’s there. 

As you know, the soda is super-saturated with CO2 that is just waiting to escape. Adding sugar and salt gives the CO2 gas exactly the opportunity it needs to leave the soda. Under certain conditions (like those in this activity) super-saturated solutions will give up whatever's dissolved in them at a far quicker rate than they would if left alone. When you added sugar or salt to your soda, the CO2 in the soda latched onto the tiny bumps on the grains of sugar and salt. Those tiny bumps (called nucleation sites) give the CO2 something to hold onto in the soda and start forming bubbles and escaping. In contrast, the oil molecules have fewer rough spots than the grains of salt and sugar, and therefore fewer nucleation sites. As a result, less CO2 escaped the soda when you added oil to it.

More to Explore

• Coke and Mentos - Exploring Explosive Chemistry, by Science Buddies
• How Sweet It Is - How Much Sugar Is Really In That Soda!, by Science Buddies
• Science Activities for All Ages!, from Science Buddies

Credits