CHAPTER 5

• Rationality


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Rational agents will select the choice which presents the highest benefits
• Producers act rationally by


  Selling goods/services in a way that maximises their profits
• Workers act rationally by


  Balancing welfare at work with consideration of both pay and benefits
• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• A firm increases advertising

  Demand curve shifts right
• Demand curve shifting right

  Increases the equilibrium price and quantity
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit you get total utility
• The Wealth of Nations was written

  1776
• When analysing markets, a range of assumptions are made about the rationality of economic agents involved in the transactions
• Complexing agent


  EDTA has 6 binding sites: 4 H on carboxylic acid groups and 2 lone pairs of electron on amine groups
• EDTA


  Hexadentate ligand that forms strong 1:1 complexes with most metal ions
• Metal-EDTA complex


  Becomes less stable at pH
• EDTA forms stable chelates with most metal ions
• Central metal atom


  Must have ability to accept 1 or more pairs of electrons in available d orbital - typically a metal ion
• Formation Constant (Kf)


  The equilibrium constant for the reaction between a metal ion (M+n) & a chelating agent
• Chelate effect


  Multidentate chelating agents form stronger complexes (Kf) with metal ions than monodentate ligands
• Monodentate ligand


  A chelating agent with only one pair of free electrons
• Multidentate ligand


  A chelating agent with more than one free electron pair
• Monodentate ligands rarely used as titrants as they provide a sharp end point generally difficult to achieve
• Multidentate ligands (tetradentate & hexadentate) are preferred for titrimetry as they react more completely with metal ion, provide sharper end-points, and usually react in a single step (form a 1:1 complex)
• Metal ion indicator


  A compound which color changes when it binds to a metal ion
• For an indicator to be useful, it must bind metal less strongly than EDTA does
• Metal ion indicators


  • Eriochrome black T (EBT), Xylenol Orange, Fast Sulphon Black, Eriochrome Red B, Patton Reeder or Murexide
• Displacement titration


  The analyte is treated with excess Mg(EDTA)2- to displace Mg2+, which is then titrated with standard EDTA
• Masking agent


  A reagent that protects some components of the analyte from reaction with EDTA
• The titration of a metal ion with EDTA is similar to the titration of a strong acid (M+) with a weak base (EDTA)
• Volumetric analysis can be acid-base, redox, or complexometry
• Oxidation


  The loss of electrons, an increase in oxidation state, the addition of oxygen, or the loss of hydrogen
• Reduction


  The gain of electrons, a decrease in oxidation state, the loss of oxygen, or the addition of hydrogen
• Redox reactions involve one element losing electrons (oxidized) and another gaining electrons (reduced)
• Balancing redox equations using the half-reaction method

  Split the original equation into two half-reactions (oxidation and reduction)

  2. Balance all elements except H and O

  3. Balance O by adding H2O

  4. Balance H by adding H+

  5. For basic conditions, add OH- to balance charges and simplify

  6. For acidic conditions, add e- to balance charges

  7. Recombine the half-reactions into a balanced equation
• Self-indication, starch indication, and redox indicators can be used to detect the end point in redox titrations
• Redox indicators


  • Ferroin, methylene blue
• Dichromate titrations require an indicator like diphenylamine, diphenylbenzidine, or diphenylamine sulfonate
• The color change for these dichromate indicators is green to violet