MCQ Detailed View

Rectified spirit is a highly concentrated form of ethanol obtained by repeated distillation of fermented liquids such as molasses or grains. It is not pure alcohol but a mixture of 95% ethanol and 5% water. The reason it cannotet be distilled beyond this point is due to the formation of an azeotropic mixture bween ethanol and water.

An azeotrope is a mixture of two liquids that boils at a constant temperature and maintains the same composition in vapor and liquid phases. For ethanol and water, this azeotrope occurs at about 95.6% ethanol and 4.4% water by volume, with a boiling point of 78.2°C. This means that during distillation, the vapor produced has the same composition as the liquid, preventing further separation by simple distillation.

Rectified spirit is commonly used in laboratories, medical preparations, and industrial applications. It serves as a solvent for many organic compounds and is also used in the manufacture of pharmaceuticals, cosmetics, and perfumes. In medicine, rectified spirit acts as a disinfectant and preservative.

The options provided can be explained as follows:

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  12% alcohol is typical of wine or beer, not rectified spirit.

  
  


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  90% alcohol can be obtained by distillation but is not rectified spirit.

  
  


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  95% alcohol is correct, as it matches the azeotropic composition.

  
  


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  100% alcohol is called absolute alcohol, which requires special drying agents like quicklime, phosphorus pentoxide, or molecular sieves to remove the last traces of water.

  
  

Therefore, rectified spirit is specifically 95% ethanol with 5% water, an important concept in organic chemistry that highlights the limitations of distillation in separating azeotropes.