Final answer:
The standard potential differences between iron and chromium, and between chromium and zinc, can be found by using the standard reduction potentials for Fe2+/Fe, Cr3+/Cr, and Zn2+/Zn from reference tables. The sum is the absolute sum of both potential differences.
Step-by-step explanation:
To determine the standard potential differences between iron and chromium, and between chromium and zinc, we use standard electrode potentials from the reference tables. Since the standard potential of a half-cell cannot be measured directly, it is always measured against another half-cell. By comparing the half-cells to a common reference, such as the Standard Hydrogen Electrode (SHE), we can indirectly determine the potential difference between them.
Unfortunately, the necessary standard electrode potentials for iron, chromium, and zinc are not provided in the question. To answer it precisely, we would look up the standard reduction potentials for Fe2+/Fe, Cr3+/Cr, and Zn2+/Zn. Let's denote these standard potentials as EFe, ECr, and EZn respectively. The potential difference between iron and chromium is given by |EFe - ECr| and the potential difference between chromium and zinc is |ECr - EZn|. The sum of these two potential differences would be the absolute sum of both values.
Note: The actual values must be obtained from standard reduction potential tables to perform these calculations.