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APchemsumacidbasebuffer05 - AP Chemistry Summary Acids...

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AP Chemistry Summary Acids, Bases and Buffers Definitions: Arrhenius: Acid - Produces H + ions in solution HCl H + (aq) + Cl - (aq) Base - Produces OH - ions in solution NaOH Na + (aq) + OH - (aq) Dissociation = Is related to the ability of a substance to "break apart" in solution. Brønsted-Lowry: Acid - Proton donor HCl + H 2 O H 3 O + (aq) + Cl - (aq) Usually H + and H 3 O + (hydronium) refer to the same thing. The hydronium form shows the hydrogen ion's association with the water molecule in the aqueous solution. (In reality the hydronium ion is probably associated with several water molecules.) Base - Proton acceptor NH 3 + H 2 O NH 4 + (aq) + OH - (aq) (In reality, ammonium hydroxide is unlikely to exist in solution but this form of the compound is consistent with the Arrhenius/Bronsted-Lowry definition.) Lewis: Acid - Electron pair acceptor (electrophile) Base - Electron pair donor (nucleophile) Ex. BF 3 + NH 3 F 3 BNH 3 In this example, the lone electron pair is donated by the nitrogen in the ammonia to the boron. BF 3 is the electron pair acceptor (acid) and the NH 3 is the electron pair donor (base). The Lewis definition is the most inclusive for identifying substances as acids or bases. The Lewis definition is beneficial in many reactions including those that do not take place in aqueous solutions and in other phases. They are particularly useful in organic chemistry and in the formation of complex ions. Strengths of Acids and Bases The strength of an acid or base is dependent upon the extent to which it performs in one of the ways as defined above (often ionizing). You should be able to differentiate between Strong vs. weak (based on the ability of the substance to dissociate) and Concentrated vs. dilute (based on the concentration (e.g. molarity) of the solute in solution. H 2 O H 2 O Hydronium Proton donor (ammonia) Proton acceptor Proton acceptor Proton donor Hydroxide Proton transfer direction Proton transfer direction
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A strong acid (such as HCl) dissociates completely, as in shown in the right facing arrow. HCl H + + Cl - A weak acid (such as acetic acid, CH 3 COOH) only dissociates to a very small degree CH 3 COOH CH 3 COO - + H + The two arrows show that the bulk of the molecules remain undissociated CH 3 COOH Strong Acids and Bases Make sure you are familiar with the 6 common strong acids HCl, HBr, HI, H 2 SO 4 , HNO 3 , HClO 4 and the 8 common strong bases LiOH, NaOH, KOH, RbOH, CsOH (hydroxides of the alkali metals) and Ca(OH) 2 , Sr(OH) 2 and Ba(OH) 2 (hydroxides of some of the alkaline earth metals. Note: Although these are considered strong bases, their solubility is actually limited) You should also know the weak base, ammonia (NH 3 ) and the weak acid, acetic acid (CH 3 COOH). These are a little tricky because NH
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APchemsumacidbasebuffer05 - AP Chemistry Summary Acids...

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