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Name: Kayla H.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 11/14/2004


Question:
After completing a lab that I created, in which I compared a basic acid cleaner, vinegar, to a basic base cleaner, laundry detergent, I noticed that the acid cleaner cleaned metal better and the base cleaner cleaned stains on cloth better. Why is this, and I no the laundry detergent cleaned the cloth better because it is laundry detergent, but why was the acid cleaner unable to do the same?


Replies:
The acidic vinegar dissolved oxidation and corrosion on the metal thus giving the appearance of "cleaning" the metal. It would not have been so effective at removing greasy dirt from the metal. The detergent has a molecular structure that is has a hydrophobic tail and a hydrophilic head. These molecules form aggregates called micelles in which the hydrophobic tails are buried inside the micelle and the hydrophilic head is oriented toward the water. Oily dirt migrates into the micelles and is held in suspension. stabilized by the hydrophilic shell.

Vince Calder


Hi Kayla,

Your lab experiment sounds intriguing. Clearly you were able to demonstrate two different types of cleaning which can occur.

For many metals, and you do not specify what you used, much of the dullness comes from the creation of an oxide layer on the surface. This coating actually helps the metal resist chemical attack to some degree. By cleaning with an acid, you were able to react with and dissolve this coating making the metal shiny again.

On cloth, most stains like dirt, etc. are non-polar. Laundry detergent is made up of non-polar surfactants which help to dissolve the stain and make it soluble in water. As you may remember from chemistry, like dissolves like. The detergent was better suited for handling non polar stains.

Bob Hartwell


Kayla,

In general, cleaning effects can be divided into two categories: (1) solubility, and (2) chemical reaction. When cleansers act to aid or speed up the dissolution of dirt into water, then the cleanser is acting like a bridge between the solvent - water, and the dirt. When the cleanser is acting like a chemical reactant, then the cleaning action is done by reacting with the dirt and changing the chemical composition of the dirt into something that is more soluble in water.

So now you need to look into how the acid in vinegar might act on metals or the particular "dirt" that is on metals, and how this might be different from the way a base-derived cleanser would act on the same "dirt.

Greg (Roberto Gregorius)



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