vanadium iii sulfate is produced by heating vanadium oxide in sulfuric acid. The concentration of sulfuric acid is generally 80% or more, and the heating temperature is 140 to 260 deg C. The vanadium oxide is not dissolved in the sulfuric acid but remains as a solid.
For the reaction to be effective, the oxidizing agent, in this case zinc, must have an Edeg value (the standard redox potential) that is less negative than the vanadium(II) ion – and for the vanadium reaction to move to the left to form the dioxovanadium(V) ion, it needs to have more of a negative Edeg value. The way you can work this out is to write down the equilibria for each step in the reduction, and compare their Edeg values. The one that is more negative will always move to the left; the more positive, to the right.