- Label the test tubesIto 8. Thenpreparea datasheet similar to the one
below and fill in theinformationas youperformthe rest of the experiment.
Follow the procedures as given in the second column of thedatasheet.
Results:Thecombinationof water and soap mixed easily with the kerosene,
lighter fluid, and magnesium sulfate. The oils, however, did not mix with water
or with water and soap together. Nomatterhowhardyou shook the mixture,
the oils alwaysseparatedwhen you allowed the mixture to stand. In other
words, the oils did not dissolve in water.
Grease is onlyanotherword for oil.Itis greasethatmakes dust and dirt
stick to clothing or skin. Sometimes this grease comes from thenormaloils in
our skin and sometimes from things we spilled, like gravy or milk. Since grease
doesn'tdissolve in water, itdoesn'tdo much good to wash dirt with water alone.
Waterand soap mixed quite easily, as you saw in this experiment. When you
added soap to a mixture of water and oil, somethinghappenedto the oil.Itno
longerseparatedout from the water. Instead, it broke up into tiny particlesthat
remained suspended in the water without dissolving in it. The water, with the
grease particles in it, constitutes anemulsion.As you remember from page 44,
an emulsion is a liquid containing small, undissolved fatty particles. Soap
cleanseffectivelybecause it emulsifies grease. Once emulsified, the grease loses
its capacity to make the dirt stick. The dirt washes away, therefore, when you
rinse the soap away.
If, however, a stain is not merely held by grease, but actually consists of
grease, soap will not succeed in washing it away. Inthatcase, you need a grease
solvent, such as carbontetrachloride.
When you added magnesium sulfate to the soap solution, it did not make any
suds. Withoutsuds, no cleaning action can take place, because it is actually
the sudsthatdo thejobof emulsifying the grease. Magnesium sulfatecontains
magnesium, an element found in many parts of the earth. If magnesium or
calcium saltshappento be dissolved in the water people use for washing and
drinking, it is called"hard"water. Nomatterhow much soap is added to hard
water, no suds form and no satisfactory cleaning can be done. The two minerals
thatmake water hard are magnesium and calciumcarbonatesand sulfates.
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