What is a pH indicator?

Learn how natural pH indicators work

Chemistry with kids often includes natural pH indicators. If you tried our color changing cabbage lab or created color changing paint, your kids and you might be wondering:

What is a pH indicator?

A pH indicator is used to measure the pH of a solution – but that seems a little circular because you are probably wondering what is pH?

pH is a property of the solution that tells you how many hydrogen ions (H+), or hydroxide ions (OH-) are wandering around in solution.

If there are a lot of excess hydrogen ions we call the solution acidic and it has a low pH.

If there are a lot of excess hydroxide ions we call the solution basic and it has a high pH.

A pH indicator is a chemical compound that can sense the amount of hydrogen or hydroxide ions in the solution. Often pH indicators work by changing color based on the acidity of the solution.

If you know the color chart for a natural pH indicator then you can read the pH of any given solution based off of what color the pH indicator turns in that solution.

natural pH indicator, comparing color pH scale of cabbage and beetroot pH indicatorsWhat are some natural pH indicators?

Natural pH indicators include purple cabbage, beetroot, turmeric, blueberries, blackberries, and even wine. Basically, any purple, blue, and orange food acts as a natural pH indicator. This is because these foods get their colors from a compound called anthocyanin, which changes its conformation, and color, based on the pH of a solution. Each natural pH indicator has their own unique color chart. You can see the difference between the cabbage pH color chart and the beetroot pH color chart displayed here.

What applications use pH indicators?

cabbage pH indicator experiment labFor kids, the applications of natural pH indicators are a whole lot of play. Because natural pH indicators change color depending on the acidity of a solution they are fun to incorporate into mixing and potion making. You can use them to dye Easter eggs, reveal hidden messagescreate color changing paint and more!

Kids can discover what items are considered acidic and basic and see if they can make connections between how edible acids and bases might taste, or the uses of acidic or basic solutions.

Gardners use pH indicators to help their plants grow well. If you are looking for a quick experiment you can look at how a set of plants grow in neutral soil (with just water), acidic soil (with citric acid crystals incorporated), and basic soil (with baking soda incorporated). How do the plants grow based on the soil pH?

As you delve deeper into chemistry pH indicators are often used to find out how much two chemicals reacted with each other. 

Hopefully, this helped you learn what is a pH indicator!