11-20-08[lecture20]tc - November 20, 2008 Chem 116 Lecture...

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Unformatted text preview: November 20, 2008 Chem 116 Lecture 20 Notes TC pH (information about): ‐ The measurement of the Hydronium ion concentration. ‐ Finding the pH of an acid given its concentration: > pH = ‐log[H+] > [H+] = Concentration in M (mols/liters) ‐ Finding the concentration ([H+]): > [H+] = antilog(‐pH) > antilog = 10x (on some calculators) > to get 10x on some graphing calculators you have to type it: 10 ^ x ‐ H3O+ are called ‘Hydronium Ions’. ‐ H+ (ions) don’t actually exist in a solution. ‐ The lower the pH, the more acidic it is. ‐ The higher the pH, the less it is acidic, and it is more basic instead. Acid‐Base Problems: > Predicting pH: ‐ Amount of Acid, Base, and/or salt (added to water) are given. ‐ The variables are ‘strong’, ‘weak’, acid, and/or base. ‐ Salts in this type of problem can break apart in water into ions that are actually weak acids or weak bases. > Equilibrium: ‐ The measurement of the pH is often given. ‐ Figuring out how much acid, base, or salt added in water in order for you to match the pH value given. > Titration: ‐ Concentration of an unknown acid or base solution is given. ‐ Neutralize it by the known amount of acid or base to get the unknown concentration. ‐ Stoichiometry is involved because a neutralization reaction is occurring. ‐ “Equivalence point” of a titration (the inflection point on the titration curve) is the point where moles of acid = moles of base ‐ Weak acids or bases involve equilibrium calculations. Strong Acids or Bases: > Strong Acids: > HCl, H2SO4, HNO3, HClO4, and HBr > Strong Bases: > Most metal cations with OH‐ ions. > Stronger acids and bases dissociate more than others or completely. The easier that ‘H+’ can be removed, it indicates that it is a strong acid. > Weak acids and bases only partially ionize. Acid‐Base Equilibria: > A general Acid Reaction has the equilibrium constant Ka. > Its form: > HA + H2O →← A‐ + H3O+ > A general Base Reaction has the equilibrium constant Kb. > Its form: > B + H2O →← HB+ + OH‐ > If an Acid‐Base reaction is given, the direction of equilibrium can be determined. Buffers: > A buffer is when approximately equal amounts of a weak acid and its conjugate base are both present in the solution. Hydrolysis: > An ion that comes from a ‘salt’. When ‘salt’ is added to water, it breaks apart into its basic + and – ions. > The broken up ions can be weak acids or bases by themselves. ...
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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