An Introduction to Acids and pH

Acids are possibly the most fundamental chemicals in nature. They can be found everywhere and chemists have been studying them for thousands of years. Finding out what they are and how we can use them is one of the first things a chemist learns. This article will explain what acids are, how to measure them and some of the ways we use them today!


An acid is something that contains positive hydrogen ions, often called H+ ions. The more H+ ions a substance has in it, the stronger it is as an acid.

Chemists use a number called pH to measure how many H+ ions are in a substance. Most substances have a pH somewhere between 0 and 14.

The lower the pH of a substance, the more H+ ions are in it. Acids have pH values lower than 7.

As well as acids (which add H+ ions) there are also chemicals called bases. They are the opposite of an acid and remove H+ ions. They have pH values higher than 7.

Some chemicals are neither acids nor alkalis and are called “neutral” substances. They have a pH of 7.


pH indicators are chemicals that change colour depending on the pH of whatever they are added to. Phenolphthalein, methyl orange and phenol red are indicators chemists use in the lab. However you can make natural DIY pH indicators yourself at home very easily! You can do this with red cabbage or turmeric powder:

Red cabbage: First, mix ¼ cup of grated red cabbage with 2 cups of water in a small pan. Next, boil the mixture until the water turns purple. Strain the mixture to remove the rest of the cabbage. The liquid we have left is now our indicator! You should find that by mixing it with acids, like vinegar and lemon juice, it should go a red to purple colour. Mixing with neutral things, like water, should make it go violet to blue. Mixing with bases, like baking soda, will give a turquoise to green colour!
Turmeric: Just mix ¼ teaspoon of turmeric powder with ¼ cup of rubbing (isopropyl) alcohol. This indicator will go yellow in acidic and neutral things but bright red in alkali things!


Being able to measure the acidity or pH of a substance is useful in a number of areas.

Different soils can have different pH values. Most plants prefer neutral or slightly acidic soils, but some prefer more acidic or even alkali soils. It is possible for farmers to check their soil’s pH and change it to match their crop if necessary. This means we can grow crops on soils that would otherwise not support them!

The conservation of lakes, rivers and the wildlife that live in them also relies on pH measurements as some animals can only survive at a certain pH. We can protect them by monitoring this.



Leave a reply

Your email address will not be published. Required fields are marked *