04-12-2012, 11:40 AM
Experiment on Saturated Solutions (Measuring Solubility)
[attachment=42373]
Introduction
A good part of the substances we deal with in daily life, such as milk, gasoline, shampoo, wood, steel and air are mixtures. When the mixture is homogenous, that is to say, when its components are intermingled evenly, it is called a solution. There are various types of solutions, and these can be categorized by state (gas, liquid, or solid). Many essential chemical reactions and natural processes occur in liquid solutions, particularly those containing water(aqueous solutions) because so many things dissolve in water. In fact, water is sometimes referred to as the universal solvent. Two examples of such important processes are the uptake of nutrients by plants, and the chemical weathering of minerals. Chemical weathering begins to take place when carbon dioxide in the air dissolves in rainwater. A solution called carbonic acid is formed. The process is then completed as the acidic water seeps into rocks and dissolves underground limestone deposits.
Basic Concepts:
A saturated solution is a mixture in which no more solute can be practically dissolved in a solvent at a given temperature. It is said practical because theoretically infinite amount of solute can be added to a solvent, but after a certain limit the earlier dissolved solute particles start rearranging and come out at a constant rate. Hence overall it appears that no solute is dissolved after a given amount of solute is dissolved. This is known as a saturated solution.
In an unsaturated solution, if solute is dissolved in a solvent the solute particles dissociate and mix with the solvent without the re-arrangement of earlier dissolved solute particles.
Solubility depends on various factors like the Ksp of the salt, bond strength between the cation and anion, covalency of the bond, extent of inter and intramolecular hydrogen bonding, polarity, dipole moment etc. Out of these the concepts of H-bonding, covalency, ionic bond strength and polarity play a major role if water is taken as a solvent.
Also physical conditions like temperature and pressure also play very important roles as they affect the kinetic energy of the molecules.
Determining Solubility
1. Measure 100 mL of distilled water and pour into a clean, empty beaker or jar.
2. Use the kitchen balance to weigh out the suggested amount (see below) of the solute to be tested.
a. 50 g Non-iodized table salt (NaCl)
b. 50 g Epsom salts (MgSO4)
c. 250 g Sugar (sucrose, C12H22O11)
3. Add a small amount of the solute to the water and stir with a clean disposable spoon until dissolved.
4. Repeat this process, always adding a small amount until the solute will no longer dissolve.
5. Weigh the amount of solute remaining to determine how much was added to the solution.
6. Try and add more solute at the same temperature and observe changes if any.
7. Now heat the solutions and add more solute to the solutions.
Precautions:
1. While adding the solute to the solvent, the solution should be stirred slowly so as to avoid the formation of any globules.
2. Stirring should not be vigorous as the kinetic energy of the molecules might change due to which solubility can increase.
3. While stirring, contact with the walls of the container should be avoided as with every collision, an impulse is generated which makes the dissolved solute particles rearrange themselves. As a result solubility can decrease.
4. The temperature while conducting all the three experiments should be approximately same.
5. Epsom salt should be first dried in order to remove the water of crystallization (MgSO4.7H2O).
[attachment=42373]
Introduction
A good part of the substances we deal with in daily life, such as milk, gasoline, shampoo, wood, steel and air are mixtures. When the mixture is homogenous, that is to say, when its components are intermingled evenly, it is called a solution. There are various types of solutions, and these can be categorized by state (gas, liquid, or solid). Many essential chemical reactions and natural processes occur in liquid solutions, particularly those containing water(aqueous solutions) because so many things dissolve in water. In fact, water is sometimes referred to as the universal solvent. Two examples of such important processes are the uptake of nutrients by plants, and the chemical weathering of minerals. Chemical weathering begins to take place when carbon dioxide in the air dissolves in rainwater. A solution called carbonic acid is formed. The process is then completed as the acidic water seeps into rocks and dissolves underground limestone deposits.
Basic Concepts:
A saturated solution is a mixture in which no more solute can be practically dissolved in a solvent at a given temperature. It is said practical because theoretically infinite amount of solute can be added to a solvent, but after a certain limit the earlier dissolved solute particles start rearranging and come out at a constant rate. Hence overall it appears that no solute is dissolved after a given amount of solute is dissolved. This is known as a saturated solution.
In an unsaturated solution, if solute is dissolved in a solvent the solute particles dissociate and mix with the solvent without the re-arrangement of earlier dissolved solute particles.
Solubility depends on various factors like the Ksp of the salt, bond strength between the cation and anion, covalency of the bond, extent of inter and intramolecular hydrogen bonding, polarity, dipole moment etc. Out of these the concepts of H-bonding, covalency, ionic bond strength and polarity play a major role if water is taken as a solvent.
Also physical conditions like temperature and pressure also play very important roles as they affect the kinetic energy of the molecules.
Determining Solubility
1. Measure 100 mL of distilled water and pour into a clean, empty beaker or jar.
2. Use the kitchen balance to weigh out the suggested amount (see below) of the solute to be tested.
a. 50 g Non-iodized table salt (NaCl)
b. 50 g Epsom salts (MgSO4)
c. 250 g Sugar (sucrose, C12H22O11)
3. Add a small amount of the solute to the water and stir with a clean disposable spoon until dissolved.
4. Repeat this process, always adding a small amount until the solute will no longer dissolve.
5. Weigh the amount of solute remaining to determine how much was added to the solution.
6. Try and add more solute at the same temperature and observe changes if any.
7. Now heat the solutions and add more solute to the solutions.
Precautions:
1. While adding the solute to the solvent, the solution should be stirred slowly so as to avoid the formation of any globules.
2. Stirring should not be vigorous as the kinetic energy of the molecules might change due to which solubility can increase.
3. While stirring, contact with the walls of the container should be avoided as with every collision, an impulse is generated which makes the dissolved solute particles rearrange themselves. As a result solubility can decrease.
4. The temperature while conducting all the three experiments should be approximately same.
5. Epsom salt should be first dried in order to remove the water of crystallization (MgSO4.7H2O).