How many gallons of water will a quart of oil pollute?

Answer 1

In general, oil will float on the water surface. That is, it will spread out in a layer on the top of the water. This is because oil is less dense than water, and is immiscible with it (meaning it doesn't mix with the water).

So if you think about it, the question is ambiguous. The answer does not depend on the volume of water (e.g. "gallons") but rather on the surface area (e.g. square feet, sq miles, etc).

For example you could have a very deep lake that contains many hundreds of thousands of gallons of water, but if the perimeter of the lake is very small, the oil may cover the entire lake. Conversely, a puddle in a parking lot may be only an inch deep, but if the puddle extends across the entire parking lot, it may contain relatively few gallons of water, but the oil may only cover a small fraction of it if the size of the puddle is very very large.

So the quest really is, how THICK will a layer of oil be if it spreads out on the water surface. Knowing this, you can calculate the amount of surface AREA that a quart of oil will spread out over.

I like to do my calculations in metric, but I'll convert back into English units for the result.

Assume that the oil makes a 1 mm film over the surface. (About 1/25th inch)

Some conversions:

1 mm = 0.1 cm

1 quart = 946 mL = 946 cm3

The area the oil would take up is the volume divided by the thickness:

A = 946 cm3/0.1 cm = 9460 cm2

So that's your estimated answer, but now let's convert it into something more meaningful.

1 m = 100 cm, so 1 m2 = 10,000 cm2

So 9460 cm2 = 0.946 m2

Rounding up slightly, we can say that this is close to 1 square meter, which is close to 1 square yard (i.e. 9 square feet).

So if the oil is 1/25th of an inch thick, the quart of oil will cover about one square yard of water (regardless of how DEEP the water is).

But remember, this was just a guess at the thickness of the oil. Additionally it assumes that the oil sticks together in a film and does not disperse.

If the oil is 10 times thinner (i.e. 0.1 mm) then the area covered will be ten times as great (i.e. 10 sq yards or 90 square feet)!