Prepare a solution of a given concentration; understand titration including acid-base reactions, pH, stoichiometry and molar equivalence.
Chemicals and equipment:
NaOH pellets close to purity, HCl 3M, phenolphtalein
Beckers, flasks, burette, magnetic or manual stir
The waste disposal will be handled through neutralization of your excess reactant to a pH between 4.0 and 10.0 and disposal with abundant rinsing. As a preparation for the lab you may want to practice with
We will do a titration in which the reaction type is acid-base. The equivalence point is characterized by a sharp change of pH which can be followed with a pHmeter. A graph of pH versus concentration will indicate the molar equivalence at the inflexion point of the curve. The point observed experimentally is never exactly the molar equivalence but a “best estimate” and is given the name “end point”. It is easier and cheaper to identify the end point with an indicator instead a pHmeter. Some chemicals such as phenolphthalein will change color when the pH changes sharply between two given values called the indicator’s range. The range of phenolphthalein is 8.3 to 10.0. The shape of a pH curve varies widely with the type of reactants and needs to be taken into account when choosing an indicator. We will titrate a strong base (NaOH) of unknown concentration with a strong acid (HCl). The objective is to find the purity of NaOH pellets. The pellets are close to purity but not 100 % because NaOH is very hydrophilic and the pellets are likely to be slightly hydrated. The procedure:
The first part of the laboratory experiment will be the preparation of the reactants and the choice of an indicator. You will need to prepare the analyte, a solution of NaOH, of a chosen concentration and volume and prepare a solution of HCl, the titrant, accordingly. Accordingly means that the end point should be reached after the delivery of...