This SIR allows you to attempt to determine the molar mass (molecular weight) of an unknown acid or base. These are not real acids and bases. Their molar masses and dissociation constants are selected by the computer at random within a reasonable range.
You select the type of unknown: acid or base; strong, weak or difunctional. The titrant of any acid will be a strong base; the titrant of any base will be a strong acid. The computer then presents you with a roughly calibrated titration curve, which allows you to select the best indicator and the amount of unknown to titrate.
You are now shown the concentration, accurate to 3 significant figures, of your titrant. Using this and the information in the approximate titration curve you must choose the mass of unknown to titrate. Good practice demands a titration volume of at least 20 mL. In the case of a difunctional unknown, you must decide which equivalence point to use.
The mass of unknown is selectable at intervals of 0.05 g, and it cycles at its extremes.
The titration proceeds as in SIR TITRATE. You fill the burette, run down to a starting point, read the initial volume, titrate to an indicator end point and compute the molar mass of the unknown.
The computer will evaluate your titration. The principal emphasis is on the accuracy of your end point and the molar mass. The computer is capable of determining whether your reported molar mass is consistent with the observations, and thus can evaluate your calculation.
This simulation allows you to perform a titration to the accuracy possible with well calibrated modern laboratory equipment: volume readings to 0.01 or 0.02 mL, end points to within about 0.03 mL, and molecular weight determinations to within a couple of tenths of a percent.
Equally important is its ability to simulate the consequences of most of the usual errors and mistakes in judgment. Used with discretion, this SIR can provide students with the equivalent of considerable experience in the laboratory.
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Updated July 17, 2000