Understanding Acids and Bases
Acids and bases can be defined using two key theories: the Arrhenius theory and the Brønsted-Lowry theory.
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Arrhenius Theory: An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions (H⁺). A base is a substance that increases the concentration of hydroxide ions (OH⁻) in solution.
- Example: HCl is an Arrhenius acid because it dissociates in water to produce H⁺ ions. NaOH is an Arrhenius base as it dissociates to produce OH⁻ ions.
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Brønsted-Lowry Theory: An acid is a proton (H⁺) donor, while a base is a proton acceptor. This theory expands the definition beyond aqueous solutions.
- Example: In the reaction between HCl and NH₃, HCl donates a proton to NH₃, making HCl the acid and NH₃ the base.
Understanding these definitions is crucial for identifying substances in various chemical reactions and for predicting their behavior in different environments.
Key points to remember
- Arrhenius acids produce H⁺ ions in water.
- Arrhenius bases produce OH⁻ ions in water.
- Brønsted-Lowry acids donate protons (H⁺).
- Brønsted-Lowry bases accept protons (H⁺).
- Both theories help classify substances in chemistry.
Worked example
Define an acid and a base according to the Arrhenius and Brønsted-Lowry theories.
- An Arrhenius acid is a substance that increases H⁺ concentration in water, e.g., HCl.
- A Brønsted-Lowry acid donates protons, e.g., HCl donates H⁺ to NH₃.