C3.4.14

Detergents

04/22/2023 GCSE Chemistry Extension Module C3.4 1

C3.4.14 • Describe the uses of sulphuric acid to illustrate its

economic importance in producing detergents

• Explain the detergent action of surfactants in lowering surface tension to remove dirt and/or oil/grease

• Describe the differences between ‘biological’ and ‘non-biological’ detergents

• Consider the effects of detergents on the environment

04/22/2023 GCSE Chemistry Extension Module C3.4 2

How is this created?

Surface tension results from an imbalance of molecular forces in a liquid.

At the surface, molecules are surrounded by other water molecules only on the water side.

WATER – SURFACE TENSION

In the body of the water, each molecule is surrounded and attracted by other water molecules.

A tension is created as the water molecules at the surface are pulled into the body of the water.

WATER – SURFACE TENSIONSurface tension causes water to bead up on surfaces (glass, fabric), which slows wetting of the surface and inhibits the cleaning process.

In the cleaning process, surface tension must be reduced so water can spread and wet surfaces.

04/22/2023 GCSE Chemistry Extension Module C3.4 6

WATER - LIMITATIONSChemicals that are able to reduce surface tension effectively are called surface active agents, or surfactants. They are said to make water "wetter."

04/22/2023 GCSE Chemistry Extension Module C3.4 7

DETERGENTSStructure

HEAD TAIL HYDROPHILIC HYDROPHOBIC LOVES WATER HATES WATER

04/22/2023 GCSE Chemistry Extension Module C3.4 8

A detergent molecule

1. Hydrophobic tail of the molecule attracted to grease and sticks into it

2. Hydrophilic head of the molecule attracted to the water and starts to pull the grease away from the fabric

3. The grease blob is surrounded by the detergent molecules that break it down into smaller blobs

DETERGENTSCleaning action

DETERGENTS - DISPOSALWhen the detergent is washed down the drain, the carbon chains of the molecule are broken down by bacteria in the water.

Biodegradability of detergents

Some early synthetic detergents had molecules which were non-biodegradable, which caused big problems in rivers, with foam forming on the surface of the river. All detergents on sale in Britain now have to be biodegradable.

DETERGENTS

The detergent created a white foam which was deadly for fish

Experts are trying to trace the source of the detergent which has devastated the fish population but left other forms of wildlife unharmed. Four miles of the River Ebbw, between Crumlin and Cwmcarn in Caerphilly borough, are hit. A misconnection in a drainage culvert is suspected.

A third unexplained pollution incident on a south Wales river has killed more than 20,000 fish.

River pollution kills 20,000 fish

DETERGENTS

One of the most threatening contaminates of storm water is soaps from the washing of cars. Carried to local waterbodies after entering storm drains, soaps cause excessive algae growth, starving the water of oxygen when the algae begins to decompose. Soaps also destroy the mucus layer in fish, which protects them from harmful parasites, and alters the aquatic environment.

Why are they bad for water quality?

DETERGENTS‘Biological’ and ‘non-biological’ detergents

Some detergents have enzymes added to them to help the detergent to remove stains containing protein, e.g. egg, and bloodEnzymes are ‘biological catalysts’ and detergents that contain enzymes are called ‘biological detergents’.

DETERGENTS‘Biological’ and ‘non-biological’ detergents

Some people find that wearing clothes that have been washed with biological detergents can cause an allergic reaction so…non-biological detergents are also available