The minimum amount of water needed to dissolve 3 mol of potassium dichromate can be calculated using its solubility data. The solubility of potassium dichromate is 12.5 g per 100 g of water at room temperature (around 25°C).

To determine the minimum amount of water required, we can set up a proportion:

(Mass of potassium dichromate) / (Solubility) = (Mass of water) / 100

Substituting the given values:

(3 mol * 294.18 g/mol) / (12.5 g / 100 g) = (Mass of water) / 100

Solving for the mass of water:

Mass of water = (3 mol * 294.18 g/mol) * (100 g / 12.5 g) = 7058.4 g

Therefore, the minimum amount of water needed to dissolve 3 mol of potassium dichromate is approximately 7058.4 g or 7.058 kg.