Chemistry of Soda

Hopewell Valley Student Podcasting Network

Chemistry Connections

Chemistry of Soda

Episode #8

Welcome to Chemistry Connections, my name is Neha and Nikhil and we are your hosts for episode #8 called Chemistry of Soda. Today we will be discussing basically that: the chemistry involved in soda.

Segment 1: Introduction to Soda

Soda is a fizzy beverage that people love to drink, ourselves included
There are many different kinds of soda. To name a couple:
Coke
Fanta
Root beer
Pepsi
And more
You can find it at any local grocery store
It is an enjoyable drink due to its carbonation and the sting it has on your tongue, which we will go into depth about shortly

Segment 2: The Chemistry Behind Soda

Topic 1: Equilibrium

First, let’s talk about the fizz in soda
Citric acid reacts with the carbonate in bicarbonate of soda to form carbon dioxide gas
These bubbles of carbon dioxide gas are what make your drink fizzy
These molecules of carbon dioxide are thoroughly mixed and dissolved into the water in the soda pop
This is known as carbonation
Regarding carbonation, it is important to note:
Carbon dioxide doesn’t easily dissolve in water under everyday conditions
Manufacturers have to increase the pressure in the can and keep it at a low temperature so water molecules can trap lots of carbon dioxide molecules
They also use pressure to put more gas in water than it could normally hold at that temperature
Therefore, if the soda can warms up a bit or the can is shaken, pressure goes up and extra gas is ready to come up
So opening the can releases pressure, and soda shoots out
This is why the can is sealed so that it is airtight. That way, the inside of the can maintains enough pressure to prevent extra carbon dioxide molecules from escaping
Talking about the can being sealed airtight, inside the can, carbon dioxide exists in two forms: some dissolves in water and some sits in gas form between the top of the can and the liquid
When carbon dioxide dissolves in water, water and gaseous carbon dioxide react to form a dilute solution of carbonic acid (H2CO3)
This reaction is reversible
When the can of soda is sealed, the high pressure inside the can forces the chemical reaction to the right (forward reaction)
This forward reaction continues until equilibrium is reached
However, once you open can, pressure is released and the reaction shifts to the left (so reverse reaction occurs)
In the reverse reaction, water and carbon dioxide are formed
This is because the gaseous carbon dioxide at the top of the can escapes when you open the can
The can is no longer under pressure if it is open, so dissolved carbon dioxide starts coming out of the solution (reverse reaction)
Bubbles form which release the carbon dioxide into the air
The escaping carbon dioxide lowers the concentration of carbon dioxide in the drink, so carbonic acid turns back to carbon dioxide and water which results in a new eqm
Now that we’re on the topic of bubbles that release carbon dioxide, let's talk about the fizz of soda going away with time
I think it’s known to most people, excluding Nikhil, that fizzy soda tastes better than flat soda
In a fizzy drink, dilute carbonic acid creates a slight burning sensation on your tongue, which is enjoyable to some
This doesn’t happen with a flat drink though
Let’s start with how the drink becomes flat
If you open a soda can or bottle, the carbon dioxide begins to come out of the soda and into the air
Eventually, enough carbon dioxide will come out and the soda will become flat
When soda is flat, carbon dioxide continually escapes which is why there is no stinging sensation when soda is flat
Let’s recall the reaction from earlier where water and carbon dioxide react to form carbonic acid
As carbon dioxide bubbles away from liquid, the reactants and products move again towards equilibrium which causes the reverse reaction to take over since carbon dioxide, a reactant, is going away so the reaction proceeds in that direction to create more of it
This causes carbonic acid concentration to get lower and lower
Therefore, as the amount of carbonic acid in the beverage goes down, so does the soda’s ability to bring about the tingling sensation on your tongue

Topic 2: Acidity/pH

Now that we’ve talked about carbonic acid, let’s talk about other acids in soda
Phosphoric acid and citric acid are added as preservatives and flavor enhancers
Citric acid specifically can bind to calcium and leach it out of teeth, which is dangerous
Every soda on the market has a pH below 4, most between 2.5 to 3.5
The acidic pH of soda makes it dangerous for teeth
This is because acid is an instrumental part of the cavity process
The acidic pH of soda gives bacteria even more power to cause cavities by lowering the pH in the mouth and weakening enamel,
Eventually, the enamel gets weak to the point where it cannot fight the acid attacks of bacteria well
Sugar in soda also feeds bacteria, which produce acid that dissolves enamel
These sugars in soda include a mixture of a sugar called glucose and another called fructose
These wo sugars attach to each other to make another sugar called sucrose
Anyway, back to the acidity of soda
The acidity of soda and absorption of carbon dioxide both can also cause a significant decrease in blood pH
This lower blood pH can possibly be associated with many diseases (including incurable cancer) because the body needs an alkaline environment for good health

Segment 3: Personal Connections

Soda is one of my favorite drinks (in my top 3)
So we thought it would be cool to take a dive into the chemistry behind soda, especially with the fizz since Neha likes fizzy soda but Nikhil does not
It was interesting to find out how the fizz works and why it fades away as time goes on
We really just chose it because it was a fun topic and soda is still something we drink weekly so it kind of is still a big part of our lives, even if it isn’t in a significant way

Thank you for listening to this episode of Chemistry Connections. For more student-ran podcasts and digital content, make sure that you visit www.hvspn.com.