During an electrochemistry lab, you carefully construct a voltaic cell with two electrodes: a lead cathode and magnesium anode based on the standard reduction potentials. You place the two electrodes on the opposite sides of a beaker divided by a porous membrane, and then fill the beaker with a solution of potassium chloride. When you connect the two electrodes using wires and a voltmeter, you notice that no voltage flows through the voltmeter. Which of the following is the most likely cause of the lack of voltage?