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Ch_08_summary - CHAPTER 8 ACIDS AND BASES(TOPICS 8 AND 18...

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CHAPTER 8 ACIDS AND BASES (TOPICS 8 AND 18) SUMMARY © IBID Press 2007 1 General properties Characteristic Properties of Acids corrosive, taste sour, and turn blue litmus red. Aqueous solutions of acids have pH < 7. Acids react with hydroxides and oxides to form salt and water; Acids react with “active” * metals to form hydrogen gas; Acids react with carbonates to produce carbon dioxide; Similarly acids react with hydrogen carbonates. Characteristic Properties of bases: Bases feel slippery, taste bitter, and turn red litmus blue. Aqueous solutions of bases have pH > 7. React with acids to form salt (and water if a hydroxide): Alkalis are bases that dissolve in water, e.g., NaOH. Substances such as ammonia, NH 3 , soluble carbonates (e.g., Na 2 CO 3 ) and hydrogen carbonates (e.g., NaHCO 3 ) are called bases; undergo base hydrolysis to form OH ; With ethylamine, ethyl ammonium ion is formed: Neutralization is the reaction of an acid and a base to give salt and water; in the salt, cations (e.g., Na + ) come from the base and anions (e.g., Cl ) come from the acid: HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) Brønsted-Lowry and Lewis theories A Brønsted-Lowry acid is a proton donor. A Brønsted-Lowry base is a proton acceptor. A Brønsted-Lowry acid-base reaction is characterised by proton transfer. When an acid transfers a proton, it produces a conjugate base. When a base accepts a proton, a conjugate acid is produced. The 2 related species in a proton transfer reaction, known as a conjugate acid-base pair, differ by a proton. HCl (aq) + CO 3 2– (aq) ' HCO 3 (aq) + Cl (aq) Acid 1 Base 2 Acid 2 Base 1 Lewis acid: a species that can accept an electron pair. Lewis acids are cations or neutral molecules with available empty orbitals, e.g., H + , Cl + , NO 2 + , CH 3 + , AlCl 3 , BF 3 . These are called electrophiles. Lewis base: a species that can donate an electron pair. Lewis bases are anions or neutral molecules with lone e pair(s), e.g., OH , Cl , H 2 O:, :NH 3 . These are called nucleophiles (or nucleophilic reagents). Electrolytes are substances that dissolve in water to give solutions containing ions. Strong Electrolyte is a substance that dissolves and completely dissociates into ions (ionises completely). This is shown by a single arrow. Weak Electrolyte is a substance that dissolves and dissociates into ions partially (to a limited extent) A strong acid ionizes or dissociates essentially completely in water, and K a , the acid dissociation constant for strong acids is large e.g., HCl, HBr, HI, HNO 3 , H 2 SO 4 , HClO 4 . "Strong" refers to complete dissociation, and “weak” refers to partial dissociation into ions. Acid strength relates to the extent of dissociation, not concentration. Concentrated solution contains larger amount of solute per dm 3 volume solution; dilute contains lower amount of solute per dm 3 volume solution (in Chemistry, strong is not the same as concentrated; weak is not the same as dilute).
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