Solubility Curves SCH 3U

Learning Goals By the end of this lesson students will be able to: Use appropriate terminology related to aqueous solutions and solubility Explain the effects of changes in temperature on the solubility of solids, liquids, and gases Analyse quantitative properties of solutions

Saturation Demo!

Solubility Saturated- solution contains all the solute it can hold at a given temperature Unsaturated- contains less solute than it can hold under existing conditions Supersaturated- contains more solute than it would normally hold at a given temperature; usually not stable, may cause solution to crystallize and precipitate out of solution

Solubility

Solubility Factors Molecule Size and Solubility Pressure Temperature Larger molecules of the solute = larger molecular mass and size Therefore it is more difficult for solvent molecules to surround bigger molecules Pressure Solid & Liquids: pressure = little effect Solubility of gas is directly related proportional to the pressure of the gas above the liquid Temperature Solids: Temperature Increase = increases solubility Liquids: Temperature Increase = little effect Gas: Temperature increases = decreases solubility Surfactant - compound like soap which reduces the surface tension with both hydrophobic and part hydrophilic helps break down hydrogen bonds and allow water to form around the oil particles Pressure is a force exerted by the substance per unit area on another substance. The pressure of a gas is the force that the gas exerts on the walls of its container.

Temperature And Solubility Solubility of Solids: When a solid dissolves in a liquid, energy is needed to break the bonds between particles in a solid Higher temperatures = greater energy Example: Caffeine's solubility in water is only 2.2g/100mL at 25oC Caffeine's solubility in water increases to 40g/100mL at 100oC

Temperature And Solubility Solubility of Liquids: The bonds between liquids are not as strong as the bonds between particles in solids When a liquid dissolves in a liquid, additional energy is not needed

Temperature And Solubility Solubility of Gases: Gas particles move quickly and have higher kinetic energies than liquids When a gas dissolves in a liquid it loses energy Increasing temperature = increases kinetic energy Increase in kinetic energy allows greater movement in the gas particles resulting in the gas coming out of solution process is exothermic

Temperature And Solubility Conclusion: A solid becomes more soluble as temperature increases. A liquid’s solubility is not greatly affected as temperature increases A gas becomes less soluble as temperature increases. Slope: A steeper slope reflects more of an effect on solubility as temperature increases.

Solubility Curves Solubility curves have: Solubility is plotted on the y axis Usually in units of g/100mL Temperature on x axis In Units of degrees Celcius Lines represent saturated solution

Saturation of Solutions Any point on the line would be a saturated solution Any point below the line, unsaturated Any point above the line, supersaturated Any solution can be made saturated, unsaturated or supersaturated by changing the temperature

Sample Problem 1 Solubility curves allow us to determine the amount of a solute that can dissolve in 100 grams of water at a given temperature. How to read the data: What amount of KCl dissolved in 100 grams of water @ 90oC? 50g dissolve per 100 ml At what temperature is the solubility of NaCl 40.0g/100g?

Sample Problem 2 How much KCl would dissolve in 500 ml @ 90oC? 50g = xg 100ml 500ml x = 50g x 500 ml 100ml x = 250 g

Sample Problem 3 A saturated solution of KNO3 in 200 g of water at 50°C is cooled to 20°C. How much KNO3 settles out? 
 @50oC: 90g = xg 100ml 200g x = 180g @20oC: 35g = xg 100ml 200g x = 70g 180g - 70g = 110g of KNO3 settle out

Homework Solubility Curve Worksheet