Video Transcript
A sample is tested using the
emulsion test with ethanol. What will the result be if the
sample contains lipids? (A) A purple solution. (B) A layer of cloudy white
emulsion. (C) A blue-black solution. (D) A brick-red precipitate. Or (E) a pale blue solution.
As suggested by this question, the
emulsion test with ethanol is a test to determine whether a substance, such as a
food item, contains lipids. In order to perform the emulsion
test, solid food is crushed using a pestle and mortar. If the sample is liquid, this step
is obviously not required. The sample is then put into a test
tube. Then, ethanol is added, and the
test tube is shaken vigorously. This allows any lipid there may be
in the food to dissolve in the ethanol.
Finally, cold distilled water is
added. Since lipids are insoluble in
water, if there are any lipids in the food sample, the lipids dissolved in ethanol
will be repelled by the water. And cloudy white droplets will
disperse through the water. This is called an emulsion. The droplets appear cloudy white
due to their scattering of light as it passes through the water. The droplets end up forming a milky
white layer at the top of the test tube, with a clear or color-transparent solution,
the aqueous layer, at the bottom of the test tube. This is the positive test result
for lipids. If the sample does not contain
lipids, the top milky white layer will be absent. That would be a negative test
result.
So the correct answer to this
question is (B). For a sample that contains lipids,
the result of the emulsion test with ethanol will be a layer of cloudy white
emulsion.
