Chapter 7 Laboratory: Solubility and Solutions 145FIGURE 7-5: Comparing the solution of unknown concentration
against samples of known concentrationoALIpToN ACTIvITIES
If you have the time and the required materials,
consider performing these optional activities:- Refine your estimated mass-volume percentage
for test tube #6 by making up additional known
concentrations of copper sulfate that bracket your
estimated value. For example, if your unknown
falls about halfway between two knowns with
concentrations of 6.0% and 12.0%, you might
estimate its concentration at about 9%. Use the
most concentrated solution (test tube #1) to make
up reference solutions at, for example, 8.0%, 8.5%,
9.0%, 9.5%, and 10.0%, and use those solutions
to determine how accurately you can estimate the
mass-volume percentage of an unknown solution by
using only your eyes.
RQEWEvI UESTIOnS
q 1 : We used copper sulfate in this lab because it is strongly colored, inexpensive, and readily available. But colorimetry is not the
best method for determining the concentration of a solution of copper sulfate. (We could instead simply evaporate the solution in test
tube #6 and determine accurately the mass of the copper sulfate it contains.) Under what circumstances would colorimetry be a good
choice for determining the concentration of a solution?
q: 2 List at least five possible sources of error that may occur with this visual colorimetry procedure.
q: 3 You are presented with an unknown solution that contains different concentrations of four food coloring dyes. Could you use
visual colorimetry to determine the concentrations of those dyes? Why or why not?