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Acid Base Equilibrium

Acid Base Equilibrium - Acids Base Equilibrium Unit IV I...

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- 24 - Chemistry 12 Schmidt Acids / Base Equilibrium Unit IV I. Arrhenius acids and bases (1884) According to Arrhenius acids are substances that dissociate in water to produce Hydrogen ions (H + ), and bases are substances that dissociate in water to produce hydroxide ions (OH - ) Acid: HCl (aq) H + (aq) + Cl - (aq) Base: NaOH (aq) Na + (aq) + OH - (aq) Arrhenius’ definition accounts for many of the properties of common acids however it has some weaknesses! 1. Definition does not apply to NON-AQUEOUS solutions. 2. The hydrogen ion is NOT responsible for acid characteristics. It is a hydronium ion (H 3 O + ) H 2 O + H + H 3 O + 3. It could not explain certain types of reactions. NH 3 + H 2 O NH 4 + (aq) + OH - (aq) base? II. Bronsted-Lowry Acids and Bases (1923) IN 1923, Johannes Bronsted and Thomas Lowry proposed a new definition for acids and bases. Their theory states that an acid is any substance that can transfer a proton (H + ion) to another substance, and a base is any substance (molecule or ion) that can accept a proton. ¾ ACID : A substance that donates a proton (H + ) in an aqueous solution. Therefore an acid is a Hydrogen donor. HCl + H 2 O H 3 O + + Cl - ¾ BASE : A substance which accepts a hydrogen ion (H + ). Therefore a base is a proton acceptor! NH 3 + H 2 O NH 4 + + OH - OH - is called a hydroxide ion H 3 O + is called a hydronium ion H + is called a hydrogen ion (proton) Other substances can act as an acid or a base. These substances are referred to as amphiprotic or amphoteric. The role played by water depends on the reaction in which it is involved! HCl + H 2 O H 3 O + (aq) + Cl - (aq) NH 3 + H 2 O NH 4 + (aq) + OH - (aq) If a substance possesses a negative charge and still has removable hydrogen It will be amphiprotic .
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