If I have a mixture of 25 vol% methanol in water and I mix it with an equal volume of dichloromethane (which is miscible with methanol but not water) can I roughly say that both phases (i.e. water and dichloromethane) will have the same methanol concentration upon reaching equilibrium? Or will it vary significantly based on the activity of each mixture?
This is a partial phase diagram. That seems to indicate that systems with roughly 50% methanol are miscible.