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Chapter 12: Problem 192

When a small amount of soap is added to a beaker of water, the soap molecules end up positioning themselves at the surface (hence soaps are often called surfactants): Explain why the soap molecules migrate to the surface, and why they orient themselves with their hydrocarbon tails sticking out of the water.

Short Answer

Expert verified
In summary, soap molecules migrate to the water's surface due to their amphiphilic nature having both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties. The hydrophilic heads are attracted to water, while the hydrophobic tails try to stay away from water, resulting in the tail sticking out of the water. This arrangement allows soap to act as a surfactant, lowering the surface tension of water and enabling it to effectively clean and create soap bubbles.

Step by step solution

01

Understanding the structure of soap molecules

Soap molecules, like all other detergent molecules, have a polar 'head' and a nonpolar 'tail'. The polar head is hydrophilic, meaning it is attracted to water. The nonpolar tail, however, is hydrophobic, meaning it repels water.
02

Understanding the behavior of these molecules in water

When soap is added to water, the hydrophilic heads of the soap molecules are attracted to the water, and the hydrophobic tails try to stay as far away from the water as they can. This results in these soap molecules arranging at the surface of the water where they can have the hydrophobic tails sticking out in the air.
03

Role of Soap as Surfactant

Due to such an arrangement of the soap molecules at the water surface, soap acts as a 'surf-actant', it lowers the surface tension of water. It basically allows the boundary between water and air to be 'flexible', which is crucial when it comes to creating things like soap bubbles or getting dirt out of clothes.
04

Summarizing the behavior of soap molecules in water

So, in summary, the soap molecules migrate to the surface of the water due to their amphiphilic nature, which means having both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties. The hydrophilic heads remain in the water, whereas the hydrophobic tails stick out away from the water. This unique arrangement allows soap to perform its functions effectively.

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Most popular questions from this chapter

At \(0.00{ }^{\circ} \mathrm{C}\) and sea level, dry air can be assumed to have a molar volume of \(22.414 \mathrm{~L}\). Given that air is \(21.0 \%\) by volume oxygen, what is the molar concentration of oxygen in the atmosphere at sea level at \(0.00^{\circ} \mathrm{C}\) ?

When \(5.00 \mathrm{~g}\) of a solute is dissolved in sufficient solvent to produce \(100.0 \mathrm{~mL}\) of solution, (a) What is the percent by mass/volume concentration of the solute? (b) What additional information do you need to calculate the percent by mass concentration of the solute, and how would you calculate that concentration once you had the missing information?

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