anachem lec midterms

• Chemical kinetics


  The study of the rates of chemical reactions and the factors that affect them
• Chemical reactions


  Processes that involve the rearrangement of atoms to produce new substances
• Precipitation


  The process of a solid forming from a solution
• Chemical equilibrium


  A state where the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of the reactants and products
• Reactions never go in just one direction
• At equilibrium, the rates of the forward and backward reactions are equal
• Equilibrium constant


  A measure of the relative amounts of reactants and products at equilibrium
• Reversible


  A reaction that can proceed in both the forward and reverse directions
• Guldberg and Waage derived an equilibrium constant by defining equilibrium as the condition when the rates of the forward and reverse reactions are equal
• Chemical reaction


  1. Collision of reacting particles

  2. Sufficient energy for collisions

  3. Proper orientation of colliding particles
• Collision theory


  Explains why different reactions occur at different rates and suggests ways to change the rate of a reaction
• Reacting particles often collide without reacting
• Activation energy


  Minimum amount of energy needed to activate or energize molecules or atoms so that they can undergo a chemical reaction or transformation
• Transition state


  The high-energy intermediate state that forms during a chemical reaction
• Le Chatelier's principle


  When stress is applied to a system at chemical equilibrium, the equilibrium will shift in a direction that tends to relieve or counteract that stress
• Le Chatelier's: Effect of Temperature


  Based on the amount of gaseous phase in a certain equilibrium reaction
• Le Chatelier's: Effect of Pressure


  Addition or removal of one of the components would cause the equilibrium to reestablish itself
• Le Chatelier's: Effect of Concentration


  Addition or removal of one of the components would cause the equilibrium to reestablish itself
• Catalysts


  Speed up or retard the rate at which an equilibrium is attained by affecting the rates of both the forward and the backward reactions
• Catalysts either increase or lower the activation energy of a certain reaction
• Peroxidase is a catalyst
• Gravimetry


  Quantitative measurement of an analyte by weighing a pure, solid form of the analyte
• Precipitation


  1. Solution phase contains more of the dissolved salt than it can carry at equilibrium

  2. Minimum number of particles must come together to produce microscopic nuclei of the solid phase

  3. The initial nucleus will grow by depositing other precipitate particles to form a crystal of a certain geometric shape
• Solubility rules


  Guidelines for predicting the solubility of ionic compounds
• Solubility rules


  • Salts containing Group I elements are soluble
  • Salts containing the ammonium ion (NH4+) are also soluble
  • Salts containing nitrate ion (NO3-) are generally soluble
  • Salts containing Cl-, Br-, or I- are generally soluble
  • Most silver salts are insoluble
  • Most sulfate salts are soluble
  • Most hydroxide salts are only slightly soluble
  • Most sulfides of transition metals are highly insoluble
  • Carbonates are frequently insoluble
  • Chromates are frequently insoluble
  • Phosphates are frequently insoluble
  • Fluorides are frequently insoluble
• Steps in gravimetric analysis

  1. Precipitation process

  2. Impurities in precipitates
• Coprecipitation


  Precipitates tend to carry down from the solution other constituents that are normally soluble, causing the precipitate to become contaminated
• Inclusion


  When ions, generally of similar size and charge, are trapped within the crystal lattice
• Occlusion


  Material that is not part of the crystal structure is trapped within a crystal
• Surface adsorption


  The surface of the precipitate will have a primary adsorbed layer of the lattice ions in excess, resulting in contamination
• Isomorphous replacement


  Two compounds have the same type of formula and crystallize in similar geometric forms, allowing one ion to replace another in a crystal
• Postprecipitation


  When the precipitate is allowed to stand in contact with the mother liquor, a second substance will slowly form a precipitate with the precipitating reagent
• Precipitation equilibria


  Insoluble compounds actually have a definite solubility (i.e., a definite amount that will dissolve) in g/L, or mol/L, at a given temperature (a saturated solution)
• Solubility constant


  A measure of the solubility of a compound
• Steps in Analytical Process


  1. Define the problem

  2. Select a method

  3. Obtain a representative sample

  4. Prepare the Sample for analysis

  5. Perform any necessary chemical separations

  6. Perform the measurements

  7. Calculate the Results and Report
• Accuracy


  Closeness to its true value
• Precision


  How close with each other
• Kinds of Error


  • Determinate (Systematic)
  • Indeterminate (Random)
• Determinate Error


  Nonrandom, occur when something is intrinsically wrong in the measurement
• Indeterminate Error


  Cannot be controlled, possible to affects measurement's precision