pH of Coca-Cola: What does the pH of a solution measure?

On a scale from 0 to 14, how much do you know about pH? What does the pH of a solution measure? What’s the pH of Coca-Cola? Don’t worry. Today, we’ll break down all you need to know about pH measurement. By the end of this article, you’ll know what pH is, how to measure the pH of a solution, and the pH of Coca-Cola and other products you recognize. Without further ado, let’s dig into it.

What is pH?

Okay, let’s start with the basics. I know, but we’ll use the basics to build up to the advanced ideas. I’ll make it quick.

A pH value refers to the concentration of hydrogen ions (H+) in a solution. The strength depends on the quantity of H+ dissociated in the solution. Strong solutions, like hydrochloric acid, release many; they dissociate almost completely. In weak solutions, like pure water, they dissociate only a little.

The hydrogen ions combine with water molecules to form hydronium ions (H3O+):

H2O + H2O ⇔ H3O+ + OH

The H3O+ concentration matches the H+ concentration, so you can say:

H2O ⇔ H+ + OH

As for the pH value, you can work with this formula:

(pH = -log H+), e.g. – log 10-7 mol [H+] = 7 pH

pH
Courtesy of Braukaiser

Now you know how to find the pH of a solution! But why is it important, anyway? Now’s a good time to talk about the main reason.

pH and your body

As sophisticated as the human sense of taste is, it can’t accurately judge pH. Which would you consider more sour, a lemon or a Coca-Cola? Naturally, we would say the lemon and guess that it has a pH lower than the pH of Coca-Cola. Of course, we’d be wrong.

The sugar in the Coke fools us. Sugar doesn’t affect the Coca-Cola pH at all. It just tricks our tongues. The lemon has a pH of around 2.5, but the pH of Coca-Cola hits 2.3 with its phosphoric acid.

When it comes to alkaline drinks, you won’t find many. Most fruit juices skew acidic, and even milk has a pH close to neutral. One drink that sits on the right side of the pH scale is green tea. However, alkaline fruits and vegetables can help you balance your body’s pH. Speaking of pH in the body, we have an important liquid in our bodies which should have its pH controlled – blood. Your blood pH should sit somewhere between 7.35 and 7.45.

 

pH
Courtesy of Seneye

And consider the pH in our drinking water, a regulated resource in most countries. A perfectly neutral water would have a pH of 7.0. However, tap water pH commonly rises above 7.0. A value below 7.0 could harm the people drinking it, not only from the acidity but also from metals dissolved from pipes damaged by the acid. On the other hand, a pH above 8.50 could harm us as well. Besides the effect on our bodies, it would weaken disinfection agents in our water.
Well, even if you didn’t know the pH of Coca-Cola, you know it’s not a healthy drink, right? Now you have the scientific base for that! Yes, I had to make that joke, and I am not ashamed.

Other applications

You’ll find pH measurement in many processes, from making cheese and producing antibiotics to creating fertilizers and mining gold. In fact, we have a video explaining how companies use pH measurement in gold production. So if you wanna know more about pH besides the pH of Coca-Cola, watch this video:

Measuring the pH of a solution – the pH electrode

With that, let’s dig more into the instrumentation side of things! A pH electrode with one measuring cell and one reference cell is the best sensor to date for finding the pH of a solution. When you immerse the electrode in a liquid, an electrical potential proportional to the liquid’s pH value builds between the two cells. Measuring this potential gives us the basis for all modern pH measurements.

The pH measuring half-cell

This half-cell has a glass membrane that, when exposed to water, forms a thin swelling layer that creates an ion exchange. We call this reaction hydrolysis. The H+ concentration in the layer changes with the pH value of the solution. This charging and discharging process continues until it creates an H+ equilibrium between layer and solution.

In the case of strongly hydrolyzed glass – due to high temperatures or alkaline applications, for example – the thickness of the swelling layer increases and the charging process takes longer. The same process occurs inside the membrane, except the H+ activity stays the same due to a fixed internal buffer.

The glass both separates the inner and outer swelling layers and connects them. The different surface potentials lead to a potential difference between the inside and the outside. To measure this difference requires zero current and a high-resistance millivolt meter.

pH measuring half-cell
Courtesy of Visaya.solutions

Depending on where and how you want to measure, different types of electrodes have different types of glass. Laboratories usually want fast responses and will need some kind of glass with low impedance. But this kind of glass wouldn’t last in a harsh environment.

The pH reference half-cell

The reference electrode must create a stable electrical baseline over time for its measurement. This is definitely the most vulnerable and complicated part of a pH electrode’s measuring chain as far as stability. Unlike the pH-sensitive glass membrane, the reference electrode comes in direct contact with the medium via a diaphragm, gap, or hole.

Therefore the electrode needs a contact point made of a chemical-resistant material. Most reference electrodes today use silver wire coated with silver chloride, which connects with the solution using an electrolyte (salt solution).

pH reference half-cell
Courtesy of Visaya.solutions

This electrolyte, based on potassium, chloride, and silver ions, gives the reference system a stable environment. It also provides an electrical bridge with the solution over the diaphragm. The electrolyte can be a liquid, a half-liquid gel, or a solid polymer.

What is a pH meter?

A pH meter is a device that you connect to your pH electrode to convert its signal into a pH value. Usually, it has a display, where you can read the value, and some kind of output signal. As we’ll learn later, the temperature can influence the measurement and the electrode. Therefore you’ll also find on the pH meter a connection where you can add a temperature probe. In most cases, you can also read the temperature on the display.

Measuring the pH of a solution
Courtesy of Endress+Hauser

Vendors

What type of system you should use depends on your process and how much money and effort you want to spend on maintenance and installation. You can find top three vendor lists for pH devices the same way you’ll find top three lists for trucks, blenders, or any other product. These manufacturers may differ depending on the application and geographical area. Check the links below to find the right alternative to measure pH of a solution.

In alphabetical order, you’ll find manufacturers of pH electrodes and instruments below:

Water/water treatment

Chemical

Pharmaceutical

Manufacturers for laboratory sensors and instruments are often different. Some manufacturers supply both, which is great for one-stop shopping and easy support for troubleshooting.

Check out these suppliers:

Water/water treatment

Chemical

Pharmaceutical

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