Ch8. Acids and Bases
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Definitions
Amphoteric: Can have the properties of both a base and an acid, depending on whether it is reacting with a base or an acid.
Brønsted-Lowry: An acid is defined as a proton donator, while a base is a proton acceptor.
Buffer: A solution that resists changes in pH when small amounts of acid or alkali are added to it.
When a small amount of acid is added, the excess of H+ ions causes the equilibrium to shift to the left -> balances the difference. When a small amount of alkali is added, the OH- ions react with the H+ ions to form water. The decrease in [H+] is compensated for by an equilibrium shift to the right. Vice versa for alkali buffers. Buffer solutions are made by several means:
**strong base + excess weak acid; **strong acid + excess weak base; **weak acid + same acid’s salt; **weak base + same base’s salt.
Concentrated: High number of moles of solute per volume of solution.
Conductivity: The more a solution is dissociated into its ions, the greater its conductivity.
Conjugate: The species remaining after an acid has lost a proton (conjugate base) or a base has gained one (conjugate acid). pKa + pKb = pKw
Diprotic: Where one mole of an acid produces two moles of hydrogen ions, e.g. H2SO4.
End point: The point at which the indicator changes colour most rapidly.
Equimolar: Containing moles at a ratio equal to the stoichiometric ratio.
Equivalence point: Where the acid and base are in equimolar quantities. Exactly enough to react with each other.
Indicator: A weak acid or base in which the dissociated form is a different colour to the undissociated form. The end point occurs when the pH is approximately equal to the pKin value. Ideally, the end point corresponds to the equivalence point in a titration.
Lewis theory: An acid is defined as an electron pair acceptor (e.g. BF3) and a base is an electron donator (e.g. NH3).
Monoprotic: Where one mole of the acid produces one mole of hydrogen ions, e.g. HCl.
pH: Power of hydrogen. – log[H+]
Salt hydrolysis: The process by which a salt is broken down by water.
Strong: An acid or a base that dissociates completely into its ions. Ka >> 1.
Some strong acids: hydrochloric, sulphuric, nitric (weaker than other two). Strong bases: hydroxides of alkali metals.
Water, ionic product of: The equilibrium constant for the dissociation of water into its ions, where [H2O] is taken to be constant. Value of Kw increases as temperature is increased, as the dissociation is an endothermic process.
Weak: An acid or base that only slightly dissociates into its ions. Ka << 1. Some weak acids: ethanoic, carbonic. *Weak bases: ammonia, aminoethane.
Presentation on acids & bases SL [.ppt]
Mindmap of the acids & bases chapter [.png]
Acid-base titration curves (weak acid on strong base) [.swf]
Acid-base titration curves (strong base on weak acid) [.swf]
How buffers work [.swf]
