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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Acids and Bases Unit 4 - 25 - Chemistry 12 Schmidt III. Characteristics of Acids and Bases ACID BASE Taste Touch Litmus Paper Ion Produced Reaction Conductivity Neutralization Bronsted acids are also classified according to how many protons can be donated per molecule. Monoprotic acid HCl , HBr; Diprotic acid H 2 SO 4 Triprotic acid H 3 PO 4 Organic acid CH 3 COOH ± Formula equations to show neutralization a) HNO 3 + KOH b) 2HCL + Ba(OH) 2 c) H 2 SO 4 + 2NaOH ± Examples of amphiprotic/amphoteric substances: a) H 2 SO 4 + H 2 O b) HSO 4 + H 2 O c) NH 3 + H 2 O IV. Conjugate Acid-Base Pairs A conjugate acid base pair is a pair of chemical species that differ by only one proton. When 1 compound acts as an acid in solution, the other acts as a base. For the reverse reaction, the compounds on the product side also act as acids and bases. H 2 SO 4 + H 2 O HSO 4 - + H 3 O + acid base base acid ± HSO 4 - is the conjugate base of H 2 SO 4 - ± H 3 O + is the conjugate acid of H 2 O Taste Sour ex. Lemons, vinegar… Taste Bitter ex. old tea, soap Feels Watery Feels Slippery Blue Red Red Blue Hydrogen Ion H + Hydroxide Ion OH - React with some metals to form H 2(g) Both conduct electricity when in solution Acid reacts with a base to produce a salt and water
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Acid Base Equilibrium - Acids / Base Equilibrium Unit IV I....

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