Cleaning Chemistry: How science scrubs away dirt

How we use simple science to clean items in our homes and workplaces

If you’ve ever washed a frying pan and become frustrated with the stubborn oily residue left behind or seen mould growing in the cracks of the kitchen tap, you know that cleaning is far more complex than giving things a lazy wipe with a cloth. The trick to cleaning effectively usually requires a combination of chemical degradation of molecules, mechanical force and rinsing to remove the dirt from the item.

Dirt comes in three broad categories: organic, inorganic and combination. Organic soils include everything from a biological source, such as grease, mould and food products. Inorganic soils include rust (which builds up when air and water react together) and minerals such as sand, silt and clay.

Most organic soils are best removed by alkaline cleaners or solvents, which work by breaking down the grease or fats, making them easier to remove by scrubbing, while inorganic soils are best tackled with acids. Acid-based sprays are most commonly used in cleaning baths, sinks and taps, where their corrosive effects will dissolve the dirt but leave the surface materials unaffected.

Specialised cleaning products, like stain remover and bleach, use various chemicals designed with this chemistry in mind. These products are applied with equipment like sponges and cloths. Together, they are the best way to keep your home free from mould, harmful bacteria and other nasties that grow in the time it takes to pile up the dirty dishes.

Organic stain remover

These chemicals, usually hydrogen peroxide, break down colour-causing molecules and are effective when the item is washed at a temperature higher than 40°C. Hydrogen peroxide needs to mix with tetraacetylethylenediamine to work at lower temperatures.

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Usually with one soft side and one rougher side, scouring pads are designed to mechanically remove dirt using friction to break the particles loose.

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Dry cleaning clothes

Dry-cleaning shops use chemical solvents other than water to wash delicate clothing and textiles that would be damaged in a washing machine or dryer.

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Dish detergent

Detergents use chemicals called surfactants that allow water to penetrate grease and separate the particles, making it easier to loosen the dirt from your plate.

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Pressyre washer

This uses a powerful jet of water under high pressure. It effectively blasts dirt off sturdy surfaces like paths and walls and washes it away.

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This article was originally published in How It Works issue 121, written by Charlie Evans 

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