What it does
Oil and water don’t mix, so water alone cannot wash oily dirt out of clothes. Soap can, because each soap molecule has two very different ends: a long oil-loving tail and a charged water-loving head. This page shows what happens in a simple model you can change:
- S sets how many soap molecules go into the water, H how many hardness ions (calcium and magnesium) it has, and O how many drops of oily dirt are on the cloth,
- the first molecules line up at the surface, tails out of the water,
- once the surface is full, the rest gather into micelles: balls with the tails inside and the heads outside. Each one picks up a drop of oil and carries it away,
- in hard water, each Ca²⁺ or Mg²⁺ ion takes two soap molecules out as grey scum, so less soap is left to clean,
- switch to Detergent and the scum disappears, because the calcium and magnesium salts of detergents dissolve.
It follows the Class 10 chapter on carbon and its compounds (soaps and detergents, micelles, hard water).
Soap is an ester split by alkali, the reverse of esterification; the alkali, sodium hydroxide, comes from the chlor-alkali process process. Why the tail avoids water comes down to polarity, shown in dipole polarity.
How to use it
- Move the S, H and O sliders, or type numbers in the boxes.
- Choose Soap or Detergent.
- The big line says whether the cloth is clean; the line under it counts micelles, free molecules and scum, and (for soap in hard water) the least soap that would clean it.
- Try the quick buttons: Soft water, Hard water and Too little soap.
A worked example
In this model, the first 20 free soap molecules stay single at the surface, every 24 more make one micelle, and each micelle holds one oil drop.
Soft water, 300 soap molecules, 4 oil drops: no scum, so all 300 are free. (300 − 20) ÷ 24 = 11.7, so 11 micelles form, more than enough for 4 drops: clean.
Hard water with 120 calcium ions: scum uses 2 × 120 = 240 soap molecules, leaving 60. (60 − 20) ÷ 24 = 1.7, so only 1 micelle forms and 3 drops stay on the cloth. The least soap that cleans is 240 + 20 + 4 × 24 = 356. With a detergent, the same 300 molecules make 11 micelles and clean it.
Tips
- The numbers are made up to keep the picture small; a real micelle has around 50 to 100 molecules, and a real wash has billions.
- Hard water can be softened (by boiling for temporary hardness, or washing soda) so soap is not wasted.
- Soap works best in soft water; detergents work in both, which is why washing powders use them.
Check yourself
Four fresh questions each time, using the model’s numbers: soap lost as scum, micelles formed, the least soap needed, and the parts of a soap molecule. Nothing is saved.
FAQ
Is this a measurement of real soap? No. It is a counting model to show the ideas: surface first, then micelles, and scum in hard water. The real amounts depend on the soap and the water.
Is this from the NCERT book? It covers the same topic with fibub’s own model and pictures. fibub is not part of NCERT.
Where the numbers come from
- The structure of soaps and detergents, micelles, saponification and scum formation with Ca²⁺ and Mg²⁺ are standard school chemistry. The numbers (20 single molecules before micelles form, 24 molecules per micelle, one oil drop per micelle) are made-up teaching values, far smaller than real ones. Written for fibub.
- Checked by hand: 300 soap molecules with 50 hardness ions lose 100 as scum, leave 200 free and make 7 micelles; the least-soap formula was checked to be exactly the smallest amount that cleans, for 0 to 5 oil drops and 0 to 56 ions.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.