Unit D - Stoich

• Stoichiometry is the process by which we are able to calculate relative quantities of the reactants and products of a chemical reaction according to chemical amount (number of moles). 
• • Stoichiometry: description of the relative quantities of the reactants and products by chemical amount, in moles.
• • We assume that all reactions are stoichiometric, spontaneous (reactions will occur), fast, and quantitative (all reactants will form products).
• • 1.Write a balanced equation for the reaction
  • 2. List  your given and your required substances.
  • 3. Set up a mole ratio using coefficients of the balanced equation for the two substances
  • 4. Substitute values in mole ratio for the given and unknown
• • Filtration is used to separate the mass of precipitate actually produced in a reaction
  • Stoichiometry is used to predict the mass of precipitate that will be produced
• • Theoretical yield is the maximum amount of product that could be formed from a given amount of reactant
  • The amount of product that forms when the reaction is carried out in the laboratory is called the actual yield
• • The actual yield is often less than the theoretical yield some reasons for this are experimental uncertainties such as:
  • All measurements 
  • Purity of chemical used
  • Washing a precipitate
  • Any qualitative judgments that affect measurements
• • Amount concentration and volume of solution are used as conversion factors to convert to or from the chemical amount of substance.
  • Recall: c= n/v
  • Amount concentration is measured in mol/L
• • Limiting reagent: reactant whose entities are completely consumed in a reaction
  •  when this substance has run out, the reaction stops
• Excess reagent: reactant whose entities are present in surplus amounts

  •  there is always extra of this substance at the end of a reaction
• Determining Excess and Limiting Reagents

  • We use an ICE table to do this:
  • I = initial moles (unreacted reactants)
  • C = change moles
  • E = end moles (the amount of moles left
• • Titration: adding a solution from a burette into an Erlenmeyer flask until a chemical reaction takes place (change in colour).
  • A process that chemists use to determine a concentration of a solution.
• • Note: the solution in the burette is called the titrant and the solution in the flask is called the sample.
• When do you stop adding Titrant to the Sample?

  • ou stop titrating when chemically equivalent amounts of reactants, as determined by the mole ratio, have been combined. 
  • This is called the equivalence point.
  • An equivalence point can be seen by an endpoint.
  • An endpoint is visible by a permanent change in colour.
• • The key to titration analysis is making sure that the endpoint  and equivalence point occur at the same time. 
  • This is achieved by using an appropriate indicator.
• • When a strong monoprotic acid completely reacts with a strong monoprotic base, the equivalence points are always neutral.
  • pH = 7
• • A buffering region occurs when the solutions are resisting a pH change.
  • It appears as the flat-line on the graph.