8.2 Factors the Affect Solubility Unit 4 - Solubility 8.2 Factors the Affect Solubility

Context – Review from Friday Things dissolve in water if they can be attracted to water Molecular compounds dissolve by being surrounded by water – the molecules themselves are not broken up Ionic compounds dissociate into ions

Ionic Compounds in Water Not all ionic compounds are soluble in water. It depends on the ionic bonds in the crystal lattice Compounds with strong ionic bonds are hard to pull apart. The water molecules will only be weakly attracted. The compound is insoluble. Compounds with weak ionic bonds are easy to pull apart. The water molecules are strongly attracted. The compound is very soluble. Use the solubility chart Dissolved ions are also called electrolytes – solution can conduct electricity

Solubility Categories Highly soluble: when more than 1.0g of the substance will dissolve in 100mL of solvent Slightly soluble: if between 0.1g – 1.0 g of substance will dissolve per 100mL Insoluble: If less than 0.1g of solute will dissolve in 100mL If something is soluble, there are certain factors that can change how soluble something is…

Factors that affect the RATE of dissolving Temperature Higher temperatures means greater kinetic energy, more collisions between solute and solvent Agitation More collisions with solute and fresh solvent Particle Size Increase the surface area for dissolution by grinding or crushing the solute into powder

Factors that Affect Solubility Molecule Size Small molecules are more soluble than large molecules Temperature Most solids have higher solubility at higher temperature Doesn’t really affect liquid-liquid solubility Gas solubility decreases at higher temperature

3. Intermolecular Forces (molecules only!) “Like dissolves Like” 4. Pressure (gases only!) Changes in pressure do not affect liquid and solids The solubility of gases is directly proportional to the pressure of the gas above the liquid

How much solute?? There is a limit to the amount of solute which can dissolve in a solvent A solution which contains the maximum amount of solute is saturated If the solution contains less than the maximum amount of solute, it is unsaturated The crystals of solute added will continue to disappear.

If there is extra solute which cannot be dissolved, the solution is supersaturated solid may and usually does come out of solution. A change in temperature (cooling a solid dissolved in liquid) can cause a saturated solution to become supersaturated

As we know, the maximum amount of solute which a solution can dissolve depends on the temperature of the solvent ** Different trends for gases We use a graph called a solubility curve to decide on masses

A solubility curve is a plot of solubility versus temperature. The line represents a saturated solution. Points below the line represent unsaturated solutions. Points above the line represent a supersaturated solution.

Solubility Curve for Ionic Compounds

What is the solubility of potassium nitrate at 80ºC ?

At what temperature will sodium nitrate have a solubility of 95 g/100 cm3 ?

What is the solubility of sodium chloride at 25ºC in 100mL of water ? From the solubility graph we see that sodium chlorides solubility is 36 g.

Solubility Curve for Gases Solubility of gases in water shows an opposite trend!

Practice! Worksheet P. 289 # 9, 10 P. 301 # 1-4