Quote:
Originally Posted by WABOOM
Petrol gasoline is very hydrophobic. But since you are a chemistry teacher...
you already know that. Tell me more about gas and water mixing. Have the molecular properties changed recently?
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Yes, gasoline is hydrophobic, but when ethanol is added, it becomes more hydrophilic. "pure" gasoline, which is made up of many types of molecules and additives, absorbs water, but very little. When you mix gasoline with water, they form two layers, but each absorbs a little from the other. There is a small amount of water dissolved in the gas, and a little bit of gas dissolved in the water.
When you add ~10% ethanol to the gas, it gets more complicated. At that percentage, ethanol fully dissolves in gas. Dissolving ethanol in gas makes the gas more hydrophilic, and so if you mix ethanol-gas with water, it will still form two layers, but you will dissolve more water into the ethanol-gas, than you would with pure gas. likewise, you will dissolve some ethanol and more gas into the water (since the water is now more hydrophibic with ethanol dissolved in it).
If you let the 2 layers sit for a while to equilibrate, you will have a layer of gas that is saturated with water and still contains ethanol, and a layer of water/ethanol that is saturated with gas. Even though ethanol is completely miscible with water, you will not be able to remove all the ethanol form the gas. To get close to complete extraction, you would need to repeat the process with fresh water multiple times. Bear in mind that in addition to removing some ethanol from gas, you are also probably removing some other additives, such as detergents as well.
For anyone who does this, aside from the potential hazards of sloshing around gallons of flammable liquid and exposure to vapors, you might also consider what you will do with the water waste that is saturated with gasoline? I hope no one is dumping this "down the drain".