Chem - Titrations of Acids and Bases

Chem - Titrations of Acids and Bases - T ITRATIONS OF A...

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Unformatted text preview: T ITRATIONS OF A CIDS AND B ASES Objective: To gain and understanding of acid and base titrations by: Observing a strong acid and strong base titration through the titration of HCl by NaOH. Observing a weak base and strong acid titration through the titration of NH 3 by HCl. Observing a weak acid and strong base titration through the titration of an unknown concentration of HC 2 H 3 O 2 by NaOH. Theory: Acids and bases are a fundamental part of chemistry. They are found in numerous chemical processes, industrial and biological, in the laboratory, and in the environment. The definition by the Swedish chemist Svante Arrhenius states that acids are substances that, when dissolved in water, increase the concentration of H + ions, while bases are substances that, when dissolved in water, increase the concentration of OH- ions. However, this definition was too limited. The definition proposed by Danish chemist Johannes Bronsted and English chemist Thomas Lowry states that acids are donators of H + ions, or protons, and bases are acceptors of H + ions. Acid-base reactions involve the transfer of H + from one substance to another. The reaction between an acid and base is called a neutralization reaction. In solution, the H + ion, which is merely a proton, forms the hydronium ion with water. The hydronium ion is represented as H 3 O + (aq) . The formation of hydronium ions is one of the more complex features of the addition of H + to water. In any given acid-base reaction, each acid and base forms a respective base and acid. These are known as conjugate acid-base pairs. Every acid forms a conjugate base through its loss of a proton, and every base forms a conjugate acid by its gain of a proton. In any acid-base reaction, two sets of conjugate acid-base pairs can be found. Some acids are typically more inclined to donate protons. Likewise, some bases are more inclined to accept protons. The more readily a substance gives up a proton, the less readily its conjugate base accepts a proton. Thus, the stronger an acid, the weaker is its conjugate base; the stronger a base, the weaker is its conjugate acid. Strong acids completely transfer their protons to water and leave no undissociated molecules in solution, and thus the conjugate bases have a negligible tendency to gain protons in aqueous solution. Weak acids only partially dissociate in aqueous solution, and therefore exist as a mixture of acid molecules and constituent ions. The conjugate bases of weak acids show a slight ability to remove protons from water. When a strong acid and strong base fully dissociates, it is a complete reaction. When a weak acid reacts, since the conjugate pairs formed can only weakly donate and gain, the reaction reaches equilibrium....
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This note was uploaded on 02/25/2012 for the course CHEM 2142 taught by Professor Roberts during the Fall '10 term at Texas State.

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Chem - Titrations of Acids and Bases - T ITRATIONS OF A...

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