For the cell $\mathrm{Zn}\left(\mathrm{s}\right)\left|{\mathrm{Zn}}^{2+}\parallel {\mathrm{Cu}}^{2+}\right|\mathrm{Cu}\left(\mathrm{s}\right)$, the standard cell voltage, ${\mathrm{E}}_{\text{cell }}^0$ is 1.10V. When a cell using these reagents was prepared in the lab, the measured cell voltage was 0.98 V. One possible explanation for the observed voltage is