Final answer:
To obtain a 0.6 M KOH solution from a 0.2 M KOH solution with an initial volume of 3 liters, 66.67% of the water needs to evaporate.
Step-by-step explanation:
To determine what percent of water should evaporate to obtain a 0.6 M KOH solution from a 0.2 M KOH solution with an initial volume of 3 liters, we use the concept of conservation of mass where the amount of solute (KOH) before and after evaporation is the same. The equation for the molarity (M) is:
M = moles of solute / liters of solution
The initial moles of KOH can be calculated as follows:
Initial moles = Initial molarity (0.2 M) × Initial volume (3 L) = 0.6 moles
Since the moles of KOH stay constant, the final volume (Vfinal) can be found using the desired molarity (0.6 M):
0.6 M = 0.6 moles / Vfinal
Vfinal = 0.6 moles / 0.6 M = 1 liter
The amount of water that needs to evaporate is 3 liters - 1 liter = 2 liters. The percentage of water that should evaporate is:
(Amount of water evaporated / Initial volume) × 100
Percentage = (2 L / 3 L) × 100 = 66.67%
Therefore, 66.67% of the water should evaporate to obtain a 0.6 M KOH solution.