Let's address each part of your query:
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Irreversible Acid-Base Reaction: The reaction of a strong acid with water is considered essentially irreversible. When a strong acid, like hydrochloric acid (HCl), dissociates in water, it completely ionizes, resulting in a significant increase in the concentration of hydrogen ions (H⁺). This reaction effectively goes to completion.
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Dissociation Constants: Your statement is correct. Hydrochloric acid (HCl) is a strong acid and dissociates completely in solution, meaning its dissociation constant (K_a) is very large, effectively approaching infinity. Acetic acid (CH₃COOH), being a weak acid, has a much smaller dissociation constant, indicating that it does not dissociate completely. Thus, \( K_a \) for HCl is indeed greater than \( K_a \) for acetic acid.
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Conductivity Order of Acidic Solutions: Conductivity in solutions is primarily determined by the concentration of ions present. Strong acids (like HCl) dissociate completely, producing a higher concentration of ions compared to weak acids (like acetic acid). Therefore, in the list provided:
- HA (presumably a weak acid, like acetic acid)
- HB (possibly another weak acid or even a strong acid, depending on its nature)
- HC (likely a strong acid)
The order from least to most conductive would likely be: HA < HB < HC, assuming HA is a weak acid, HB is another weak or a lesser strong acid, and HC is a strong acid.
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Effect on pH: Decreasing the concentration of OH⁻ ions in a solution will lead to an increase in the concentration of H⁺ ions, as the system shifts to maintain equilibrium. According to the relationship pH = -log[H⁺], if [H⁺] increases, the pH will decrease. Therefore, decreasing the concentration of OH⁻ ions in a basic solution would indeed lead to a decrease in pH.
If you have any more questions or need further clarification, feel free to ask!
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