explain why adding soap to water will help remove dirt and oil?

Question

3 questions in one
why does a needle float on water

why does the needle sink after soap is added to the water

Answer 1

Soap contains enzymes that break down the oil, these enzymes allow the soap and water to mix.

A needle floats on water due to surface tension.

The soap breaks the surface tension (or breaks the bonds of the water).
The proteins in soap (enzymes) act as catalysts

Answer 2

Soap is made up of what is called a surfactant; surfactant is simply a molecule that has a charged head, with a very long hydrophobic tail; surfactant has traditionally been derivatives of fat. When soap is dropped into water, the hydrophobic tails will zoom together and the surfactant form what's called a micelle. Things like dirt and oil, which usually sits in a separate layer than water, will start to break up and sit into these spherical micelles, and the layer of what you might recognize as "fat" is simply your surfactant holding the oil and dirt.

A needle can float on top of water by surface tension. This also explains why some insects can crawl across water. But to accomplish this, the needle must be placed carefully on top of the water - any disturbance will make the needle lose its grip and it will sink.

When you add soap to water, the soap disturbs the normal hydrogen bonds that makes the water's surface tension so strong. Instead of hydrogen bonding with each other, the water begins to hydrogen bond with the polar head of the surfactant; also, the water must deal with the long hydrophobic tail. This effectively ruins the surface tension, and the needle sinks.

Answer 3

1. Water is hydrophillic and dirt & oil are hydrophobic (dear lord i hope you know what that means or this will make no sense). The two are in seperate solutions, so dirt/oil will not dissolve in water to be carried away and thus sticks to your hand. Soap is a "detergent" (yes the actual scientific name) and, much like a magnet, has hydrophobic and hydrophillic regions which interact with both the water and the dirt/oil allowing the solutions to dissolve.

2. A needle floats on water due to the high surface tension causes by hydrogen bonding in water molecules

3. After soap is applied the hydrogen bonds are disrupted because they now interact with the soap, rather than the tightly bound net of water molecules. The surface tension is no longer high and the needle sinks.

Answer 4

Soaps are sodium salts of long chain fatty acids. How do soaps remove grease from your hands?



In water, the molecules ionize and leave a charged [COO-] head to the fatty acid. This charged head is attracted to water but the long carbon tail is not. As a result, several of these charged fatty acid molecules come together and form a "ball" with the charged heads facing outwards and the hydrophobic tails facing into the center of the ball. In this arrangement, this "micelle" of fatty acids can be surrounded by water molecules. Grease is hydrophobic and will be attracted and isolated in the middle of the micelle where it also is hydrophobic. When you wash your hands with soap, the micelle, which is surrounded by water, will carry away the grease trapped in its center.


enzymes??? hmmm :S

Answer 5

A soap molecule is a long one with one end somewhat ionic and the other covalent, so it will bind onto oil (covalent) and water (ionic) at the same time, and the oil is washed away.

Answer 6

Soap traps dirt molecules and when you rinse they all go bye bye.

Answer 7

problematic problem. research using yahoo or google. that might help!