Why hydrocarbons are not soluble in water

Part of the cleaning action of soap results from the fact that soap molecules are surfactants they tend to concentrate on the surface of water. Water can't wash the soil out of clothes by itself because the soil particles that cling to textile fibers are covered by a layer of nonpolar grease or oil molecules, which repels water.

The nonpolar tails of the soap molecules on the surface of water dissolve in the grease or oil that surrounds a soil particle, as shown in the figure below. The soap molecules therefore disperse, or emulsify , the soil particles, which makes it possible to wash these particles out of the clothes. Most soaps are more dense than water. They can be made to float, however, by incorporating air into the soap during its manufacture. Most soaps are also opaque; they absorb rather than transmit light.

Translucent soaps can be made by adding alcohol, sugar, and glycerol, which slow down the growth of soap crystals while the soap solidifies. The primary reason for the decline in the popularity of soap is the reaction between soap and "hard" water.

Hard water interferes with the action of soap because these ions combine with soap molecules to form insoluble precipitates that have no cleaning power. These salts not only decrease the concentration of the soap molecules in solution, they actually bind soil particles to clothing, leaving a dull, gray film.

Many water softeners are filled with a resin that contains -SO 3 - ions attached to a polymer, as shown in the figure below. When this happens, it has to be regenerated by being washed with a concentrated solution of NaCl. There is another way around the problem of hard water. Synthetic detergents are examples of such cleaning agents.

Detergent molecules consist of long, hydrophobic hydrocarbon tails attached to polar, hydrophilic -SO 3 - or -OSO 3 - heads, as shown in the figure below.

By themselves, detergents don't have the cleaning power of soap. These builders are often salts of highly charged ions, such as the triphosphate P 3 O 10 5- ion. Cloth fibers swell when they are washed in water. This leads to changes in the dimensions of the cloth that can cause wrinkles -- which are local distortions in the structure of the fiber or even more serious damage, such as shrinking. These problems can be avoided by "dry cleaning," which uses a nonpolar solvent that does not adhere to, or wet, the cloth fibers.

The nonpolar solvents used in dry cleaning dissolve the nonpolar grease or oil layer that coats soil particles, freeing the soil particles to be removed by detergents added to the solvent, or by the tumbling action inside the machine.

Dry cleaning has the added advantage that it can remove oily soil at lower temperatures than soap or detergent dissolved in water, so it is safer for delicate fabrics. When dry cleaning was first introduced in the United States between and , the solvent was a mixture of hydrocarbons isolated from petroleum when gasoline was refined.

The concentration of a solution is defined as the amount of solute dissolved in a given amount of solvent or solution. The molarity M of a solution is defined as the ratio of the number of moles of solute in the solution divided by the volume of the solution in liters. At 25 o C, a saturated solution of chlorine in water can be prepared by dissolving 5. Calculate the molarity of this solution.

Click here to check your answer to Practice Problem 3. Click here to see a solution to Practice Problem 3. Mass percent is literally the percentage of the total mass of a solution that is due to the solute. The concentration of a solution in units of moles per liter can be calculated from the mass percent and density of the solution.

It is also possible to describe the concentration of a solution in terms of the volume percent. This unit is used to describe solutions of one liquid dissolved in another or mixtures of gases. Molarity is the concentration unit most commonly used by chemists.

It has one disadvantage. It tells us how much solute we need to make a solution, and it gives us the volume of the solution produced, but it doesn't tell us how much solvent will be required to prepare the solution.

We can make a 0. But how much water is enough? Because the CuSO 4 5 H 2 O crystals occupy some volume, it takes less than a liter of water, but we have no idea how much less. When it is important to know how much solute and solvent are present in a solution, chemists use two other concentration units: molality and mole fraction. The molality m of a solution is defined as the number of moles of solute in the solution divided by the mass in kilograms of the solvent used to make the solution.

The total volume of the solution, however, will be larger than 1 liter because the CuSO 4 5 H 2 O crystals will undoubtedly occupy some volume. As a result, a 0. A saturated solution of hydrogen sulfide in water can be prepared by bubbling H 2 S gas into water until no more dissolves. Calculate the molality of this solution if 0.

Click here to check your answer to Practice Problem 4. Click here to see a solution to Practice Problem 4. With the polar and nonpolar mix, this does not occur and the two distinct layers form.

The concept of like dissolves like has practical applications. In the laundry room, detergents dissolve in water, decreasing its polarity and dissolving oils for better cleaning. However, applying a prewash solution, containing slightly polar organic solvents that dissolve in water while retaining enough nonpolar characteristics to dissolve grease stains, offers a more effective method of stain removal.

World View. What is the lewis structure for co2? What is the lewis structure for hcn? How is vsepr used to classify molecules? What are the units used for the ideal gas law? How does Charle's law relate to breathing?

What is the ideal gas law constant? How do you calculate the ideal gas law constant?