Final answer:
To find the emf of a voltaic cell under standard conditions, you need to look up the standard reduction potentials for the redox couples involved in the cell reaction and calculate the sum. Unfortunately, the standard potentials for the Ce⁴⁺/Ce³⁺ and Cr³⁺/Cr²⁺ redox couples are not provided, so you will need to consult a reliable source to find these values and calculate the emf.
Step-by-step explanation:
The emf (electromotive force) of a voltaic cell under standard conditions can be determined using the standard cell potential (E°cell). In this case, the reaction is given as:
3Ce⁴⁺(aq) + Cr(s) → 3Ce³⁺(aq) + Cr³⁺(aq)
The standard cell potential of this reaction can be found in a table of standard reduction potentials. Look up the reduction potentials for the Ce⁴⁺/Ce³⁺ and Cr³⁺/Cr²⁺ redox couples, and then find the overall reaction standard potential by summing these values. Once you have the standard potential, you can use the Nernst equation to account for non-standard conditions.
Unfortunately, the reduction potentials for Ce⁴⁺/Ce³⁺ and Cr³⁺/Cr²⁺ are not provided in the provided information. Please refer to a reliable source, such as a textbook or reference guide, to find the standard potentials for these redox couples and calculate the emf of the cell.