Question

(Evaluating the Equilibrium Constant for the Reaction of Iron(III)Ion with Thiocyanate Ion)

1. When measuring the volumes of Fe(NO3)3 and NaSCN solutions in this experiment, the student mistakenly used a graduated cylinder instead of volumtetric pipets, After collecting all of the data, the student realized he'd used the wrong piece of equipment, but he didn't redo the experiment. Also, he later realized that he had consistenly misread the graduated cylinder and had thus transferred volumes that were actually 5% lower that the recorded volumes.

Incoportate these measurement errors into the data for one of your equilibrium solutions, and recompute Keq for that solution. Determine whether the student's measurements errors would cause each of the following, as recalculated by you, to be higher than, lower than, or identical to the value you originally determinded. Briefly explain.

1) the calculated SCN- ion concentration in standard solution

2)the slope of the Beer's law plot

3) the calculated equilibirum solution concentrations

4) calculated Keq

Answer 1

Influence of experimental error

1) By using the graduated cyllinder instead of pipet, the resulting calculated SCN- concentration would be higher than the actual concentration for the standard solution.

2) the slope which is dependent upon the concentration would thus be lower than the actual value.

3) The calculated equilibrium concentrations would also be higher as all the concentrations have changed by the fixed number (5% lower value)

4) Calculated Keq : would not change as it the ratio of equilibrium concentrations.