MCQ Detailed View

Surfactants are surface-active agents that reduce the surface tension of water and help in cleaning by emulsifying oils, greases, and dirt. Their effectiveness can vary depending on the type of surfactant and the nature of water, especially its hardness and pH. Water hardness is mainly caused by dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions, which can react with some surfactants and reduce their efficiency.

Surfactants are classified into four main categories: anionic, cationic, nonionic, and amphoteric.

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  Anionic surfactants carry a negative charge. They are excellent foaming and cleaning agents but perform poorly in hard water because calcium and magnesium ions form insoluble salts with them.

  
  


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  Cationic surfactants carry a positive charge. They are more useful as disinfectants and fabric softeners rather than as general cleaning agents, and their activity is limited under variable water conditions.

  
  


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  Nonionic surfactants do not carry any charge on their hydrophilic group. Instead, they rely on polar functional groups like alcohols, ethers, or polyethylene oxides. Since they lack electrical charge, they are not affected by the presence of calcium or magnesium ions in hard water. This unique property makes them suitable for use in both soft and hard water. Moreover, they are stable across a broad pH range, whether acidic, neutral, or alkaline.

  
  


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  Amphoteric surfactants can act as anionic or cationic depending on pH, but they are not the standard choice for commercial detergents.

  
  

Because of their stability, nonionic surfactants are widely used in dishwashing liquids, shampoos, industrial cleaning agents, textile processing, and emulsifiers. They provide reliable cleaning action across various conditions, which makes them superior when water hardness and pH vary significantly.

Thus, the type of surfactant that performs effectively across a wide range of water hardness and pH is nonionic surfactants.