In this chapter, you have seen that the voltage of an electrochemical cell is sensitive to the concentrations of the reactants and products in the cell. As a result, electrochemical cells can be used to measure the concentrations of certain species in solution. For example, the voltage of an electrochemical cell based on the reaction H2(g) + Cu2+(aq)-2 H+ + Cu(s) is sensitive to both the Cu2+ concentration and the H+ concentration in solution. If the H+ concentration is held constant, then the voltage only depends on the Cu2+ concentration, and we can use the cell to measure the Cu2+ concentration in an unknown solution. The tabulated data show the measured voltage in the hydrogen/copper electrochemical cell just discussed for several Cu2+ concentrations. Examine the data and answer the questions that follow.
a. Construct a graph of the measured voltage versus the the copper concentration. Is the graph linear?
b. Determine how you might manipulate the data to produce a linear graph. (Hint: See the Nernst equation.)
c. Reconstruct a graph of the data using the method to produce a linear graph from part b. Determine the slope and y-intercept of the best-fitting line to the points in your graph. Could you have predicted the slope and intercept from the Nernst equation?
d. The voltage of two unknown solutions are measured and recorded. Use the slope and intercept from part c to determine the Cu2+ concentrations of the unknown solutions.