Factors Affecting Solubility

Topics: Solubility, Solution, Concentration Pages: 9 (2481 words) Published: November 14, 2012
There are three main factors that control solubility of a solute. (1) Temperature
(2) Nature of solute or solvent
(3) Pressure
Generally in many cases solubility increases with the rise in temperature and decreases with the fall of temperature but it is not necessary in all cases. However we must follow two behaviours: In endothermic process, solubility increases with the increase in temperature and vice versa. For example: solubility of potassium nitrate increases with the increase in temperature. In exothermic process, solubility decrease with the increase in temperature. For example: solubility of calcium oxide decreases with the increase in temperature. Gases are more soluble in cold solvent than in hot solvent. NATURE OF SOLUTE AND SOLVENT

Solubility of a solute in a solvent purely depends on the nature of both solute and solvent. A polar solute dissolved in polar solvent. Solubility of a non-polar solute in a solvent is large. A polar solute has low solubility or insoluble in a non-polar solvent. EFFECT OF PRESSURE

The effect of pressure is observed only in the case of gases. An increase in pressure increases of solubility of a gas in a liquid. For example carbon dioxide is filled in cold drink bottles (such as coca cola, Pepsi 7up etc.) under pressure. Properties of Solution

The concentration of a solution is the measure of how much solute and solvent there is. A solution is concentrated if it contains a large amount of solute, or dilute if contains a small amount. Molarity

Molarity is the number of moles of solute per litre of solution. It is abbreviated with the symbol M, and is sometimes used as a unit of measurement, e.g. a 0.3 molar solution of HCl. In that example, there would be 3 moles of HCl for every 10 litres of water (or whatever the solvent was). Molality

Molality is the number of moles of solute per kilogram of solvent. It is abbreviated with the symbol m (lowercase), and is sometimes used as a unit of measurement, e.g. a 0.3 molal solution of HBr. In that example, there would be 3 moles of HBr for every 10 kilograms of water (or whatever the solvent was). Mole Fraction

The mole fraction is simply the moles of solute per moles of solution. As an example, you dissolve one mole of NaCl into three moles of water. Remember that the NaCl will dissociate into its ions, so there are now five moles of particles: one mole Na+, one mole Cl-, and three moles water. The mole fraction of sodium is 0.2, the mole fraction of chloride is 0.2, and the mole fraction of water is 0.6. The mole fraction is symbolized with the Greek letter (chi), which is often written simply as an X. Dilution

Dilution is adding solvent to a solution to obtain a less concentrated solution. Perhaps you have used dilution when running a lemonade stand. To cut costs, you could take a half-full jug of rich, concentrated lemonade and fill it up with water. The resulting solution would have the same total amount of sugar and lemon juice, but double the total volume. Its flavour would be weaker due to the added water. The key concept is that the amount of solute is constant before and after the dilution process. The concentration is decreased (and volume increased) only by adding solvent. Thus, the number of moles of solute before and after dilution are equal. moles1 = moles2

By definition of molarity, you can find the moles of solvent.
M x V = moles
Substituting the second equation into the first gives the dilution equation.
M1 x V1 = M2 x V2
To determine the amount of solvent (usually water) that must be added, you must know the initial volume and concentration, and the desired concentration. Solving for V2 in the above equation will give you the total volume of the diluted solution. Subtracting the initial volume from the total volume will determine the amount of pure solvent that must be added.

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