Would you expect the conductivity reading to be high or low, and increasing or decreasing, in each of these situations?
Equivalence Point
In this experiment, you will monitor conductivity during the reaction between sulfuric acid, H2SO4 and barium hydroxide, Ba(OH)2, in order to determine the equivalence point. You will need to recall what you learned from Lab 6 and the conductivity of electrolytes and nonelectrolytes. From the conductivity data you collect, you can find the concentration of the Ba(OH)2 solution. You will also see the effect of ions, precipitates, and water on conductivity. The equation for the reaction in this experiment is:
Ba2+(aq) + 2 OH – (aq) + 2 H+(aq) + SO4
2–(aq) BaSO4(s) + H2O(l)
Before reacting, Ba(OH)2 and H2SO4 are almost completely dissociated into their respective ions. Neither of the reaction products, however, is significantly dissociated. Barium sulfate is a precipitate and water is predominantly molecular.
As 0.0200 M H2SO4 is slowly added to Ba(OH)2 of unknown concentration, changes in the conductivity of the solution will be monitored using a Conductivity Probe. When the probe is placed in a solution that contains ions, and thus has the ability to conduct electricity, an electrical circuit is completed across the electrodes that are located on either side of the hole near the bottom of the probe body (see Figure 1). This results in a conductivity value that can be read by the interface. The unit of conductivity used in this experiment is the microsiemens, or µS/cm.
Figure 1
Prior to doing the experiment, it is very important for you to hypothesize about the conductivity of the solution at various stages during the reaction. Would you expect the conductivity reading to be high or low, and increasing or decreasing, in each of these situations?
When the Conductivity Probe is placed in Ba(OH)2, prior to the addition of H2SO4.
As H2SO4 is slowly added, producing BaSO4 and H2O.
When the moles of H2SO4 added equal the moles of BaSO4
