Determine the voltage of the electrochemical cell. Zn(s) + 2e- -> Zn E°= -0.76 V, Ni2+ (aq) + 2e- -> Ni E°= -0.25 V. State what would be observed when ethanoic acid reacts with CaCO3. Calculate the volume of oxygen required to burn completely 4 moles of C3H8 at s.t.p.

The species with the more negative standard reduction potential will be oxidized. In this case, $\text{Zn}$ has a more negative $E^\circ$ ($-0.76 \text{ V}$) compared to $\text{Ni}$ ($-0.25 \text{ V}$).
Therefore, $\text{Zn}$ will be oxidized (anode) and $\text{Ni}^{2+}$ will be reduced (cathode).

Anode (oxidation): $\text{Zn}(s) \longrightarrow \text{Zn}^{2+}(aq) + 2e^- \quad E^\circ_{ox} = +0.76 \text{ V}$
Cathode (reduction): $\text{Ni}^{2+}(aq) + 2e^- \longrightarrow \text{Ni}(s) \quad E^\circ_{red} = -0.25 \text{ V}$

The voltage of the electrochemical cell is $\boxed{\text{0.51 V}}$.

From the balanced equation, $1 \text{ mole}$ of $\text{C}_3\text{H}_8$ reacts with $5 \text{ moles}$ of $\text{O}_2$.

At s.t.p., $1 \text{ mole}$ of any gas occupies $22.4 \text{ dm}^3$.

The volume of oxygen required is $\boxed{\text{448 dm}^3}$.