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Following a recent discussion on the relationship of pH to alkalinity, I received a number of messages from cleaners who wanted a better understanding of the chemistry associated with cleaning but found too much scientific gobbledygook confusing.  
 
The following is an attempt to address some of the issues without getting too technical. I have taken slight liberties for the purpose of simplification and avoided such matters as adhesion and cohesion.  
 
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The Wet Stuff
   

The basis of the vast majority of the cleaning we do is water.
 
This simple element, composed of two hydrogen atoms and one oxygen, essential to all life on our planet, is largely taken for granted but can serve as an introduction to chemistry for the cleaner who does not want to get too involved in the science of cleaning.
 
The hydrogen atom is quite content to wander the planet on its’ own. Oxygen atoms, on the other hand are lonely things who do not relish the single life. Take a bucket of oxygen and before you know it they have teamed up in pairs (O2). Introduce some hydrogen atoms and under the right circumstances the friendly little oxygen chaps will persuade the loners (hydrogen) to form the family unit we know as water (H2O).
 
This newly formed family is very happy to include new members and will readily combine with many other substances it encounters, making it the most universal solvent known to man.
 
One introduction to the water family that we engineer is to include another oxygen atom to produce hydrogen peroxide (H2O2). Although it was oxygen that was initially responsible for forming the water family, this new oxygen atom is not comfortable in it’s new home and will readily latch on to molecules of a different substance. This is the basis of using oxidizing agents for stain removal.
 
One other thing we can do to water is to introduce additional energy in the form of heat. When we do this, the atoms in the individual molecules move around faster, causing expansion. This extra space is partly responsible for the fact that as water heats up it becomes a better solvent.
 
Even at low temperatures water is keen to change its’ state from liquid to vapour – the process we know as evaporation. Molecules are constantly trying to escape the liquids’ surface and the more energy (heat) in the water, the more succeed in escaping. Hence hotter water not only cleans better but dries quicker. As the molecules escape the surface and integrate with the air immediately above the liquids’ surface the air approaches its’ saturation point which is why the use of an air mover to clear away this water-laden air and replace it with drier air speeds up drying.  
 
Another substance that is commonly used in cleaning is the detergent. This family has a love/hate relationship with water. One branch of the molecule loves the stuff (is hydrophilic), whilst the other end hates it (is hydrophobic). Consequently the hydrophobic end will latch on to just about anything that is not water. If we then take the water away (extract), the hydrophilic end does its’ utmost to follow. Since the hydrophobic ends have attached themselves to non-water molecules (including the soil in a carpet) they act as ‘chemical tow-ropes’. Between the solvency of the water and the ‘towing’ of the detergent we then have a wash action.
 
In addition to detergents, we employ other additives to water to assist us in the cleaning process.
 
Oils are generally not water soluble but emulsifiers enable them to be suspended within water.
 
Enzymes are proteins that have the ability to break down other proteins into their component parts, thereby easing removal.
 
Cationic surfactants have the ability to neutralize a static electric bond which holds some types of soil (e.g. soot) to fibres. Formulations for soot removal also contain wetting agents which enable water to penetrate soot particles and set up a bond.
 
Of course, we do use solvents other than water – aromatics (mainly distillates of petroleum and alcohols) – but without the wet stuff our cleaning would be very different and much more expensive.

© 2004 J E Bolton MBICSc