Properties of Acids

All acids contain hydrogen ions (H+). These determine how strong or weak an acid is. For example, strong acids release all hydrogen ions when added to water, transforming the water into an acidic solution. On the other hand, weak acids only let go of some of their hydrogen ions, making for a less concentrated solution.

So, the higher the concentration of hydrogen ions in water or aqueous solutions, the stronger the acid. Strong acids typically have pH levels between 1 and 3, while weak acids register in the 4-6 range on the pH scale.

pH = power of hydrogen. The pH scale, which runs from 0 to 14, measures how many hydrogen ions are present in a water-based solution. The pH scale goes like this:

0-6: acid

7: neutral

8-14: base

Acids and Bases – What’s the Difference?


Characteristic Acid Base
Behavior in aqueous solutions Acidic substances release hydrogen ions (H+) in aqueous solutions. Bases release hydroxide ions (OH-) when added to water.
Smell Acids can have a powerful, acrid odor. Typically base substances are odorless, with ammonia being the main exception.
Taste Sour. Bitter – a bit like eating soap.
Feel Acids should be treated carefully – they can cause skin irritation and burning. Bases can feel slippery because they react with the fatty acids in your skin. Some commands are also harmful, so take care when handling them.
Litmus test result Acids will turn the litmus paper from blue to red. No change on its own. Able to neutralize results of a positive acid test and return litmus paper to blue.
Can they conduct electricity? Yes, in aqueous solutions Yes, in aqueous solutions
pH level < 7 > 7

Common Acids

Acids aren’t just confined to the science lab; they’re a large part of everyday life. From food to cleaning products and fizzy drinks to digestion, acids have a hidden role in many aspects of our daily lives. Here are five of the most common everyday acids:

  1. Acetic acid – or HC2H3O2, to its friends – gives vinegar its sharp flavor. Malt vinegar is between 5-20% acetic acid.
  2. Carbonic acid is an aqueous solution of carbon dioxide to water, known as carbonated or fizzy water.
  3. Citric acid is a natural acid in all citrus fruits, e.g., lemons and limes.
  4. Hydrochloric acid is a solution of hydrogen chloride in gastric acid, which helps us break down and digest food. Also known as HCl, hydrochloric acid is a strong, corrosive acid.
  5. Sulphuric acid is a highly corrosive substance in car batteries and cleaning products.

Facts about Acids

  • Under the Bronsted-Lowry definition, an acid is any substance capable of donating a proton or hydrogen ion.
  • A Lewis acid is a compound that forms a covalent bond by absorbing electron pairs.
  • An Arrhenius acid is a substance that increases the number of hydrogen ions in a water solution.
  • To be considered an acid by any definition, a substance must have a pH level of below 7.
  • The word acid comes from the Latin words “acidus” and “acere,” meaning sour.
  • The chemical opposite of an acid is a base. Base substances contain negatively charged hydroxide ions (OH-) and can neutralize acids. Bases that are not water-soluble are known as alkalis.
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