Surface tension allows pond skaters and other insects to walk across water and also allows a pin to float. You can demonstrate this yourself by taking a bowl of water and floating a pin on the surface.
Carefully add just one drop of washing-up liquid and see what happens to the pin. It should sink immediately because the detergent molecules break apart the forces holding the water together. The pin is no longer supported and so sinks to the bottom! You can measure surface tension yourself by making your own button balance, like the one used by the famous nineteenth century home experimentalist, Agnes Pockels.
You will need:. You can set up the balance in one of two ways, as shown in the diagram above. You'll soon find out which one works best for you. The lollystick is used for the lever and the nylon thread has the advantage of not soaking up water and influencing the balance. The piece of card can be suspended from the lollysick with the nylon thread to act as a counterbalance pan.
To use your balance:. With your button balance, try measuring the surface tension of a range of liquids and comparing them. For example: cold water, salt water, warm water and soapy water. You can also try changing the size of the button used or the material it is made out of.
About us. Detergents are the next most abundant ingredients in shampoo. Detergents are surfactants that react with the surface in order to remove oil and dirt particles from the hair follicle. Common detergents include ammonium laurel sulfate, sodium laurel sulfate, and sodium laurel ether sulfate. The sulphates are made from either natural or synthetic linear CC15 alcohols. Thickeners are then added in order to increase viscosity. Popular thickeners include sodium chloride and methylcellulose.
Shampoo strips the hair of its sebum, which is required to protect the hair shaft. Therefore, shampoos must also contain an ingredient to replace the lost sebum.
Silicones, polymers, and quaternary agents coat the hair and replace the lost sebum. Because shampoos consist of mostly water and organic compounds, preservatives such as parabens are added to prevent the growth of bacteria and maintain freshness.
Ophardt, Charles E. Elmhurst College, Virtual Chembook. From Wikibooks, open books for an open world.
Soap [ edit edit source ] Soap is a form of lipid which is a mixture of sodium salts of various naturally occurring fatty acids. Structure [ edit edit source ] Micelles are formed when a certain molecule are added with water.
Types of Soap: The unique properties of different soaps are based on the type of fatty acid and length of the carbon chain of the molecule. Cleansing Action of Soap: The cleansing action of soap is determined by its amphipathic properties- polar and non-polar structures, as well as its solubility characteristics.
What you need: Jam jar or other small container with lid Cooking oil Water Washing up liquid How to: Put some cooking oil and water in the jam jar. Screw the lid on tightly and shake. Let the jar stand for a few minutes. What do you notice? The oil and water should separate into layers. Add a few drops of washing up liquid to the oil and water and screw the lid on tightly again. Shake and leave for a few minutes. What do you see? You should see a cloudy mixture.
The oil and water are no longer in separate layers. Carboxylic acids and salts having alkyl chains longer than eight carbons exhibit unusual behavior in water due to the presence of both hydrophilic CO 2 and hydrophobic alkyl regions in the same molecule.
Such molecules are termed amphiphilic Gk. Fatty acids made up of ten or more carbon atoms are nearly insoluble in water, and because of their lower density, float on the surface when mixed with water.
Unlike paraffin or other alkanes, which tend to puddle on the waters surface, these fatty acids spread evenly over an extended water surface, eventually forming a monomolecular layer in which the polar carboxyl groups are hydrogen bonded at the water interface, and the hydrocarbon chains are aligned together away from the water.
This behavior is illustrated in the diagram on the right. Substances that accumulate at water surfaces and change the surface properties are called surfactants.
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