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Correct Answer: a and b
the arrhenius theory, formulated by svante arrhenius in the late 19th century, provides a fundamental explanation of acid-base chemistry, specifically defining acids as substances that increase the concentration of h+ ions in water, and bases as substances that increase the concentration of oh- ions in water. this theory, however, has its limitations, particularly when considering acid-base reactions that occur outside aqueous solutions or involve compounds that do not fit neatly within these definitions.
one significant limitation of the arrhenius theory is its applicability only to reactions occurring in aqueous solutions. this theory does not account for acid-base reactions that can occur in other solvents or in a solvent-free environment. for instance, the reaction between gaseous hydrogen chloride (hcl) and ammonia (nh3), which forms solid ammonium chloride (nh4cl), cannot be explained by the arrhenius theory because it does not involve the formation of h+ and oh- ions in water.
additionally, the arrhenius theory fails to adequately describe the behavior of certain substances that act as bases but do not produce hydroxide ions when dissolved in water. common examples include ammonia (nh3) and sodium bicarbonate (nahco3). ammonia, a typical base, does not contain hydroxide ions but nonetheless increases the ph of water by reacting with water molecules to form ammonium (nh4+) and hydroxide (oh-) ions. similarly, sodium bicarbonate acts as a base due to its ability to neutralize acids, but it does so through a reaction that produces bicarbonate (hco3-) and carbonate (co32-) ions, again not involving direct formation of oh- ions.
these examples illustrate that the arrhenius theory is constrained by its reliance on the presence of water and the specific formation of hydroxide ions for bases, and hydrogen ions for acids. the theory does not cover acid-base reactions where these specific ions are absent or where the reaction medium is not water. this has led to the development of more generalized theories, such as the brønsted-lowry and lewis theories, which accommodate a broader range of acid-base phenomena across different solvents and without the strict requirement for ion formation as specified by arrhenius.
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