Which element is common to all acids?

All acids, whether organic or inorganic, contain the element hydrogen. The presence of hydrogen is what gives acids their characteristic properties, such as sour taste, ability to turn blue litmus red, and their ability to react with bases to form salts and water.

For example:

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  Hydrochloric acid (HCl) contains hydrogen bonded to chlorine.

  
  


• 
  

  Sulfuric acid (H₂SO₄) contains hydrogen bonded to the sulfate group.

  
  


• 
  

  Acetic acid (CH₃COOH) contains hydrogen in the carboxyl (-COOH) group.

  
  

The reactive hydrogen atom in acids is often referred to as a proton (H⁺). When an acid dissolves in water, it releases H⁺ ions, which are responsible for the acidic behavior of the solution. This is why hydrogen is universally present in all acids, regardless of the other elements present in the molecule.

Other options are incorrect:

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  Carbon is only present in organic acids like acetic acid, but not in inorganic acids such as HCl or H₂SO₄.

  
  


• 
  

  Sulphur is present only in sulfur-containing acids like H₂SO₄, but not in all acids.

  
  


• 
  

  Oxygen is common in many acids, but some acids, like hydrochloric acid (HCl), do not contain oxygen.

  
  

Understanding the role of hydrogen in acids is fundamental to chemistry, as it explains reactions like neutralization, acid-base titrations, and pH calculations. Hydrogen is the defining element that allows acids to donate protons, making it the common element in all acids.

This knowledge is essential in everyday science to understand chemical reactions, industrial applications, and biological processes, since acids are widely used in food, medicine, and laboratory experiments.