C3.4.14 Detergents

1. C3.4.14 Detergents GCSE Chemistry Extension Module C3.4

2. 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 GCSE Chemistry Extension Module C3.4

3. How is this created?

4. WATER – SURFACE TENSION Surface tension results from an imbalance of molecular forces in a liquid. In the body of the water, each molecule is surrounded and attracted by other water molecules. At the surface, molecules are surrounded by other water molecules only on the water side. A tension is created as the water molecules at the surface are pulled into the body of the water.

5. WATER – SURFACE TENSION Surface 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.

6. WATER - LIMITATIONS Chemicals that are able to reduce surface tension effectively are called surface active agents, or surfactants. They are said to make water "wetter." GCSE Chemistry Extension Module C3.4

7. DETERGENTS Structure HEAD TAIL HYDROPHILIC HYDROPHOBIC LOVES WATER HATES WATER GCSE Chemistry Extension Module C3.4

8. DETERGENTS Cleaning action A detergent molecule 1. Hydrophobic tail of the molecule attracted to grease and sticks into it 3. The grease blob is surrounded by the detergent molecules that break it down into smaller blobs 2. Hydrophilic head of the molecule attracted to the water and starts to pull the grease away from the fabric GCSE Chemistry Extension Module C3.4

9. DETERGENTS - DISPOSAL Biodegradability of detergents When the detergent is washed down the drain, the carbon chains of the molecule are broken down by bacteria in the water. 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.

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

11. DETERGENTS Why are they bad for water quality? 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.

12. 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 blood Enzymes are ‘biological catalysts’ and detergents that contain enzymes are called ‘biological detergents’.

13. 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