Where can we find acids and alkalis in nature?

Image: Richard Bartz, 2007. Bee stings contain formic acid and are slightly acidic. Wasp stings, on the other hand, are slightly alkaline.

What are acids and bases?

Before we delve into the different acids and bases found in nature, we need to be clear about what they actually are. In their simplest definition acids are solutions that have a pH below 7 and react with bases in neutralization reactions which means that the acid effect is cancelled out by the base. A more advanced explanation would add that acids release in hydrogen ions (H+) in water.

Bases are the chemical opposite of acids. Their pH values are above 7 and they react with acids in neutralization reactions. You may also have heard the word alkali being used for bases. Alkalis are bases that are soluble in water and release hydroxide ions (OH-). In this article we will use the word alkalis.

Food and digestion

There is one strong acid that you are carrying around with you all the time, the hydrochloric acid in you stomach. Your stomach acid is quite strong with a pH of 2. Its job is to break down food and kill pathogens that enter the digestive system. Pathogens are microorganisms like bacteria and viruses that can cause diseases.

Most of you will have heard that there is a lot of acid in citrus fruit like lemon. They contain an acid called citric acid which also gives them their sour taste. Lemon juice has a very acidic pH between 2 and 3. However, other fruits and vegetables contain acids too. For example, there is malic acid in apples. Tomatoes and pears contain citric acid as well as malic acid.

A sour taste will tell us if food or drinks are acidic. We can also tell from the taste if they are alkaline. The give-away for alkalis is a bitter taste. Examples of alkaline foods are leafy green vegetables like kale, spinach and parsley.

Insect bites and stings

So far we have only talked about beneficial acids and alkalis in food, drinks or our stomach. However, there are some unpleasant acids and alkalis to be found in nature as well.

Bee and ant venoms contain formic acid making their stings or bites slightly acidic contributing to the pain they cause. In fact, formic acid was first extracted from ants which lead to it being named after the Latin word for ant ”formica”. Nevertheless, we need to be aware that insect poisons are a mixture of different unpleasant substances that work together in a sting. Bees and ants do not rely on the formic acid in their venom alone.

Wasp venom, on the other hand, is slightly alkaline. Just like in bees and ants wasp poison too is a cocktail of various chemicals which contribute to the effect of a sting. Also wasps need other substances apart from the alkali in their venom.

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