Following precipitation reactions with conductivity measurements
KünyeESLEK, Z., TULPAR, A. (2013). Following precipitation reactions with conductivity measurements. Journal of Chemical Education, 90 (12), pp. 1668-1670. http://dx.doi.org/10.1021/ed300594f.
This general chemistry laboratory exercise is based on the analysis of precipitation reactions via conductivity. In the first part of the experiment, the aim is to teach students how to prepare solutions from a solid (Na2CO3) and by dilution from a stock solution [Cu(NO3)(2)]. In the second part of the experiment, the students use the solutions to perform precipitation reactions: (1) Cu(NO3)(2) (aq) + Na2CO3 (aq) and (2) Cu(NO3)(2) (aq) + 2 NaOH (aq). Observations are made on the appearance of the solutions and the precipitates. Conductivities of the solutions are measured at each step of the experiment. For the laboratory report, students perform stoichiometric calculations to determine the theoretical conductivities of the reaction mixture. The students also calculate hypothetical conductivities of the mixture in the case of no precipitation reaction and compare them with the measured data. Most of the students conclude that the number and concentration of free ions decrease during these precipitation reactions. Overall, the students learn how to prepare solutions and gain experience in doing conductivity measurements and stoichiometric calculations.