Activity

Activity 1

Activity 2

Factors Affecting Solubility

Glory Grace E. Ortiga

Ivan Mary A. Pascual

De La Salle University-Dasmarinas

Dasmarinas, Cavite Philippines

ABSTRACT

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The activity entitled Factors Affecting Solubility demonstrated how temperature and polarity of solute and solvent affects solubility. A gram of KCl was heated to 40ºC in an ignition tube. The solution was stirred and noted of the take noted of the solubility of KCl. Another gram of KCl was added to the mixture and does the same procedure again. The whole procedure was repeated with NaCl. The solubility of solids in liquids with the effect of temperature shows that the higher the temperature the higher the solubility will be. On the other hand, in determining the effect of polarity of the solute and solvent experiment, it resulted that the highly polarity of the solvent, the higher the miscibility is. In the third procedure, which is the influence of another substance, a pinch of iodine crystal shakes with 10mL water. It was added a pinch of potassium iodide crystals and shake the mixture and it resulted to highly solubility.

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INTRODUCTION

Thesolubility of a solute is the maximum quantity of solute that can dissolve in a certain quantity of solvent or quantity of solution at a specified temperature. The solubility of a solid in a liquid is most affected by temperature, nature of solute particles, and nature of the solvent particles. In general, an increase in temperature increases the solubility of a substance but there are some exceptions to this rule. In order for a solvent to dissolve a solute, the particles of the solvent must be able to separate the particles of the solute and occupy the intervening spaces. Polar solvent molecules can effectively separate the molecules of other polar substances. This happens when the positive end of a solvent molecule approaches the negative end of a solute molecule. A force of attraction then exists between the two molecules. The solute molecule is pulled into solution when the force overcomes the attractive force between the solute molecule and its neighbouring solute molecule. Ethyl alcohol and water are examples of polar substances that readily dissolve in each other.

In the case of gases, an increase in temperature decreases the solubility of gases in liquids while

increased pressure increases their solubility.

Polar solvent dissolve polar solutes to produce solutions, while non-polar solvents dissolve non- polar solutes. The rule of thumb then is “Like dissolves like”. A substance tends to dissolve in a solvent which is chemically related in composition to the substance.

The rate of solution is a measure of how fast a substance dissolves. Some of the factors determining the

rate of solution are size of the particles, stirring, amount of solute already dissolved and temperature.

MATERIALS AND METHODS

A gram of KCl was heated at 400C in an ignition tube. The solution was stirred and take noted of the solubility of KCl. Another gram of KCl was added to the mixture and do the same procedure again. The whole procedure was repeated with NaCl.

A gram or 1mL of the solutes of potassium chloride, coconut oil, toluene, copper sulfate was determined

the solubility in 1mL water, 1mL isopropyl alcohol and 1ml (1:1V/V water: isopropyl alcohol.

Factors Affecting Solubility

Temperature

Basically, solubility increases with temperature. It is the case for most of the solvents. The situation is though different for gases. With increase of the temperature they became less soluble in each other and in water, but more soluble in organic solvents.

Polarity

In most cases solutes dissolve in solvents that have a similar polarity. Chemists use a popular aphorism to describe this feature of solutes and solvents: "Like dissolves like". Nonpolar solutes do not dissolve in polar solvents and the other way roud.

Pressure

• Solid and liquide solutes

For majority of solid and liguide solutes, pressure does not affect solubility.

• Gas solutes

As for gasses the Henry's law states that solubility of gas is directly proportional to the pressure of this gas. This is mathematically presented as: p = kc, where k is a tempreture dependent constant for a gas. A good proof of Henry's law can be observed when opening a bottle of carbonated dring. When we decrease the pressure in a bottle, the gas that was dissolved in the drink bubbles out of it.

Molecular size

The larger the molecules of the solute are, the larger is their molecular wieght and their size. It is more difficult it is for solvent molecules to surround bigger molecules. If all of the above mnetioned factors ale excluded, a general rule can be found that larger particles are generaly less soulble. If the pressure, and temperature are the same than out of two solutes of the same polarity, the one with smaller particles is usually more soluble.

Stirring increares the speed of dissolving

Stirring does not have an affect on solubility of a substance, but everyone knows that if he puts sugar in his tea and does not stirr, it will not dissolve. Actually, if we left the tea to stand for a long enough time, the sugar would dissolve. Stirring only increases the speed of the process - it increases move of the solvent what esposes solute to fresh portions of it, thus eabling solubility. As molecules in liquide substances are in costant move, the process would take place anyway, but it would take more time.

Factors Affecting Solubility 2

The solubility of a solute is the maximum quantity of solute that can dissolve in a certain quantity of solvent or quantity of solution at a specified temperature.

 The main factors that have an effect on solubility are:

	the nature of the solute and solvent  --  While only 1 gram of lead (II) chloride can be dissolved in 100 grams of water at room temperature, 200 grams of zinc chloride can be dissolved.  The great difference in the solubilities of the of these two substances is the the result of differences in their natures.
	temperature  --  Generally, an increase in the temperature of the solution increases the solubility of a solid solute.  A few solid solutes, however, are less soluble in warmer solutions.   For all gases, solubility decreases as the temperature of the solution rises.
	pressure  --  For solids and liquid solutes, changes in pressure have practically no effect on solubility.  For gaseous solutes, an increase in pressure increases solubility and a decrease in pressure decreases solubility.  (When  the cap on a bottle of soda pop is removed, pressure is released, and the gaseous solute bubbles out of solution.  This escape of a gas from solution is called effervescence.)

 The rate of solution is a measure of how fast a substance dissolves.  Some of the factors determining the rate of solution are:

	size of the particles  --  When a solute dissolves, the action takes place only at the surface of each particle.  When the total surface area of the solute particles is increased, the solute dissolves more rapidly.  Breaking a solute into smaller pieces increases its surface area and hence its rate of solution.  (Sample problem:  a cube with sides 1.0 cm long is cut in  half, producing two pieces with dimensions of 1.0 cm x 1.0 cm x 0.50 cm.  How much greater than the surface area of the original cube is the combined surface areas of the two pieces? 2.0 cm2
	stirring  --  With liquid and solid solutes, stirring brings fresh portions of the solvent in contact with the solute, thereby increasing the rate of solution.
	amount of solute already dissolved  --  When there is little solute already in solution, dissolving takes place relatively rapidly.  As the solution approaches the point where no solute can be dissolved, dissolving takes place more slowly.
	temperature  --  For liquids and solid solutes, increasing the temperature not only increases the amount of solute that will dissolve but also increases the rate at which the solute will dissolve.  For gases, the reverse is true.  An increase in temperature decreases both solubility and rate of solution.

 Solubility and the nature of a solvent and a solute:

	In order for a solvent to dissolve a solute, the particles of the solvent must be able to separate the particles of the solute and occupy the intervening spaces.  Polar solvent molecules can effectively separate the molecules of other polar substances.  This happens when the positive end of a solvent molecule approaches the negative end of a solute molecule.  A force of attraction then exists between the two molecules.  The solute molecule is pulled into solution when the force overcomes the attractive force between the solute molecule and its neighboring solute molecule.  Ethyl alcohol and water are examples of polar substances that readily dissolve in each other.
	Ammonia, water, and other polar substances do not dissolve in solvent whose molecules are nonpolar.  The nonpolar molecules have no attraction for polar molecules and exert no force that can separate them.  However, nonpolar substance such as fat will dissolve in nonpolar solvents.
	Polar solvents can generally dissolve solutes that are ionic.  The negative ion of the substance being dissolved is attracted to the positive end of a neighboring solvent molecules.  The positive ion of the solute is attracted to the negative end of the solvent molecule.  Dissolving takes place when the solvent is able to pull ions out of their crystal lattice or structure.  The separation of ions by the action of a solvent is called dissociation.  When you sprinkle table salt (NaCl) in water and stir, the grains of salt disappear.  From what you have just read (on solubility), you have a model to explain what actually happens to the salt.  Sodium chloride, an ionic compound, is made of sodium ions and chloride ions.  The slightly charged ends of water molecules attract these ions.  As a result the ions are dissociated, or separated by the water molecules and spread evenly throughout the solution.

Dissolving

Factors Affecting Solubility