There are several factors that affect the rate of dissolving a solute in a solvent. These include surface area, movement, and temperature. Show Sometimes we want a thing to dissolve quickly because we get bored sitting in front of a beaker watching it. Sometimes we want a larger quantity of a solute to dissolve than we could normally achieve. Before this section, both of these things would be impossible. However, now that you understand how solutions work, I feel confident in handing you the following ways of affecting solubility. Surface Area of the SoluteLet's imagine that you're trying to dissolve 1.0 grams of sodium chloride in a glass of water. Which would dissolve more quickly: a large 1.0 gram crystal or 1.0 grams of salt ground into a fine powder? If you guessed that the powder would dissolve more quickly, you're right. Because the powder has a larger surface area than the crystal, more of the ions in the salt are exposed to the solvent at any given time, causing them to dissolve more quickly. It should be noted that breaking a solute into smaller pieces doesn't change how much of it will dissolve, it only changes how quickly it will dissolve. PressureWhen dissolving a gas within a liquid, the pressure of the gas has a huge effect on its solubility. When the pressure of a gas is low, the number of gas molecules that hit the surface of the liquid at any given time is low; as a result, there are fewer chances for the gas to dissolve. However, if the pressure of the gas is increased, the number of collisions between the gas molecules and the solvent increases, which causes more of the gas molecules to dissolve.
The relationship between pressure and solubility was first expressed in 1801 in Henry's Law:
When divers are deep underwater, the pressure of the water increases the amount of gas from the air they breathe that dissolves in their blood. As they rise, the pressure goes down and the gas becomes less soluble, forming small bubbles in the bloodstream. Because gas bubbles accumulate in one's joints, rising too quickly can increase this amount of gas to dangerous levels. The agony caused by this condition causes people to curl up in the fetal position, so it's called "the bends." In this equation, P represents the pressure of the gas above the solvent, k is a mathematical constant with positive value that depends on the particular solution being studied, and C represents the concentration of the gaseous solute in the solution. As you can see from the equation, the higher the pressure of the gas, the more concentrated the solution will be. Though pressure is an important factor in the solubility of a gas, pressure has very little effect on the solubilities of liquids or solids. TemperatureThe temperature of a liquid affects the solubility of both solids and gases. Generally, increasing the temperature of a solvent increases the solubility of most ionic compounds (though there are exceptions). More important, increasing the temperature of a solvent usually increases the rate at which a solute dissolves, which is why it's easier to dissolve sugar in hot tea than cold tea. Gases, on the other hand, become less soluble as the temperature of the solution increases, which is why carbonated beverages (which contain CO2) go flat more quickly on hot days than on cold ones. Excerpted from The Complete Idiot's Guide to Chemistry © 2003 by Ian Guch. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc. To order this book direct from the publisher, visit the Penguin USA website or call 1-800-253-6476. You can also purchase this book at Amazon.com and Barnes & Noble.
IntroductionLiquids In LiquidsSolids In LiquidsGases In Liquids IntroductionA solution is a homogeneous mixture of one or more solutes in a solvent. Sugar cubes added to a cup of tea or coffee is a common example of a solution. The property which helps sugar molecules to dissolve is known as solubility. Hence, the term solubility can be defined as a property of a substance (solute) to dissolve in a given solvent. A solute is any substance which can be either solid or liquid or gas dissolved in a solvent. On this basis, the factors affecting solubility vary on the state of the solute:
Liquids In LiquidsWater is known as a universal solvent as it dissolves almost every solute except for a few. Certain factors can influence the solubility of a substance. Solubility is the new bond formation between the solute molecules and solvent molecules. In terms of quantity, solubility is the maximum concentration of solute that dissolves in a known concentration of solvent at a given temperature. Based on the concentration of solute dissolves in a solvent, solutes are categorised into highly soluble, sparingly soluble or insoluble. If a concentration of 0.1 g or more of a solute can be dissolved in a 100ml solvent, it is said to be soluble. While a concentration below 0.1 g is dissolved in the solvent it is said to be sparingly soluble. Thus, it is said that solubility is a quantitative expression and expressed by the unit gram/ litre (g/L). To Know About Solvents And Solutes, Watch The Below Video:
Based on solubility, different types of solution can be obtained. A saturated solution is a solution where a given amount of solute is completely soluble in a solvent at given temperature. On the other hand, a supersaturated solution is those where solute starts to salting out or precipitate after a particular concentration is dissolved at the same temperature. Factors Affecting Solubility:The solubility of a substance depends on the physical and chemical properties of that substance. In addition to this, there are few conditions which can manipulate it. Temperature, pressure and the type of bond and forces between the particles are few among them.
Solids In LiquidsIt has been observed that solid solubility depends on the nature of solute as well as the solvent. We often see that substances like sugar, common salt (NaCl), etc readily dissolve in water while substances like naphthalene do not dissolve in water. From the various observations and experimental results, it has been seen that only polar solutes tend to dissolve in the polar solvent and non-polar solvents dissolve only non-polar solutes. Hence, the nature of solvent can be seen as one of the prominent factors affecting solubility. The above observation led to the statement that like dissolves like, that is polar solvents will dissolve polar solutes and non-polar solvents dissolve non-polar solutes. Crystallization: Now let us understand the process by which a solid dissolves in a solvent. Once a solid solute is added to a solvent, the solute particles dissolve in the solvent and this process is known as dissolution. Solute particles in the solution collide with each other and some of these particles get separated out of the solution, this process is called crystallization. A state of dynamic equilibrium is established between these two processes and at this point, the number of solute molecules entering the solution becomes equal to the number of particles leaving the solution. As a result, the concentration of the solute in the solution will remain constant at a given temperature and pressure. A solution in which no more solute can dissolve in the solvent at a given temperature and pressure is said to be a saturated solution as the solution contains the maximum amount of solute. The concentration of solute in such a solution is called its solubility at that temperature and pressure. If more solute can be added to a solution than it is called an unsaturated solution. Factors Affecting Solubility
Gases In LiquidsGas solubility in liquids deals with the concept of gas dissolving in a solvent. Let us first define solubility. For any substance, solubility is the maximum amount of solute that can be dissolved in a given solvent at a particular temperature. Now our concern is gas solubility in liquids. The gas solubility in liquids is greatly affected by temperature and pressure as well as the nature of the solute and the solvent. There are many gases that readily dissolve in water, while there are gases that do not dissolve in water under normal conditions. Oxygen is only sparingly soluble in water while HCl or ammonia readily dissolves in water. Factors Affecting Solubility
Hydrated salts are solutions of liquid in solid. The solubility of a solute decreases with increase of temperature if dissolution is exothermic. As pA = KHxA . Thus, at constant temperature, for same partial pressure of different gases, xA ∝ 1/KH . So, higher the value of KH, lower is the solubility of the gas. Dissolution of gas in liquid is an exothermic process. As the temperature is increased, equilibrium shifts backwards. For more details and examples join us on byjus.com or download BYJU’S – The Learning App.
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