--- title: Soap and why washing works — a lesson of Mova's school · trees and pragmatics description: «Soap and why washing works», a lesson of the chemistry course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: After pizza your fingers are greasy, and rinsing under the tap does almost nothing: water and grease do not mix. --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Chemistry](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/) / Soap and why washing works # Soap and why washing works Lesson 24 of the chemistry course of Mova's primary school: 19 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/chemistry/24-soap-and-why-washing-works/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/0/) — After pizza your fingers are greasy, and rinsing under the tap does almost nothing: water and grease do not mix. - [1](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/1/) — Add soap and the grease slides away. - [2](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/2/) — Each soap particle has a water-loving head and a grease-loving tail; the tails grab the grease and the heads pull it into the water. - [3](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/3/) — Soap also breaks apart many germs, which is why washing your hands properly, for about 20 seconds, or two rounds of "Happy Birthday", helps stop illness. - [4](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/4/) — Soap weakens the "skin" of water, its surface tension. - [5](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/5/) — Sprinkle pepper on water, touch it with a soapy finger, and the pepper races to the edges, pulled by the stronger skin there. - [6](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/6/) — Soapy water also makes a stretchy film that you can blow into bubbles, and a free bubble always pulls itself into a ball. - [7](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/7/) — Long ago people made soap by boiling fat with lye from wood ash, a very harsh alkali, so not a kitchen experiment. - [8](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/8/) — Today washing powders also carry enzymes that break down food stains, and hand gel uses alcohol to kill germs, though it does not lift dirt. - [9](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/9/) — Each soap particle has a water-loving head and an oil-loving tail; the tails grab grease and the heads pull it into the water. - [11](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/11/) — Soap weakens the surface tension of water; the stronger "skin" at the edges pulls pepper away from a soapy finger, and a paper boat with soap at the back zooms forward for the same reason. - [12](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/12/) — Soap makes the water's skin flexible so it does not snap, which is why plain water cannot be blown into bubbles; a little glycerine or sugar makes bubbles last longer. - [13](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/13/) — A free bubble always becomes a sphere, because a sphere holds the air inside with the smallest surface; even square wire frames make round bubbles. - [14](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/14/) — In hard-water areas, minerals in the water react with soap to make grey scum, and kettles get white crusts of limescale. - [15](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/15/) — In history, soap was made by boiling fat with lye from wood ash; the alkali breaks fats into soap, and lye is very caustic. - [16](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/16/) — Washing powder contains detergents and enzymes that break down protein and fat stains, so many modern powders work well at 30 °C and save energy. - [17](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/17/) — Foam is just lots of bubbles; soap particles do the cleaning whether there is foam or not. - [18](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/18/) — Dishwasher detergent is made not to foam, so washing-up liquid must never go in a dishwasher: the foam would overflow. - [19](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/24-soap-and-why-washing-works/19/) — Alcohol hand gel kills many germs by damaging their outer coat, but it does not remove dirt, works poorly on dirty hands, is flammable and must not be swallowed. - ← previous: [Browning apples, rotting and mould](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/23-browning-apples-rotting-and-mould/) - next →: [Cleaning chemicals and safety at home](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/25-cleaning-chemicals-safety/) - ↑ back to [Chemistry](https://md.mova.elamur.ai/free/en/corpora/school/chemistry/)