1. Solutions – Learning Outcomes  Define solute, solvent, solution.  Examine and describe the difference between dilute, concentrated, and saturated solutions.  Define solubility.  Investigate solubility in water and the effect of temperature on solubility. 1

2. Solutions – Learning Outcomes  Draw a solubility curve.  Define crystallisation.  HL: Grow crystals using alum or copper sulfate. 2

3. Solutions  Consider making a cup of coffee.  Coffee starts as grains or powder. 3

4. Solutions  The grain breaks apart into smaller pieces – it has partially “dissolved”. 4

5. Solutions  Eventually the grain is completely broken up – it has fully dissolved. 5

6. Solutions  We say the coffee is a solute because it dissolves in the water.  The water is a solvent because it dissolves the coffee.  The mixture of coffee dissolved in water is called a solution. 6

7. Solutions  A solvent is a substance that dissolves other materials to form a solution.  A solute is a substance that dissolves in a solvent.  A solution is a mixture of a solute and a solvent.  If a material can dissolve in a solvent, it is said to be soluble (e.g. coffee in water).  If a material cannot dissolve in a solvent, it is said to be insoluble (e.g. sand in water). 7

8. Solution examples 8

9. Solutions  Which of these will dissolve in water?  Cocoa powder  Sand  Dirt 9

10. Concentration  Depending on how much solute is dissolved, we use different words to describe the resulting solution.  Dilute solutions have little solute dissolved in a lot of solvent.  Concentrated solutions have a lot of solute dissolved in a little solvent.  Saturated solutions have as much solute dissolved as possible at that temperature. 10

11. Solubility  How many spoons of sugar will dissolve in a cup of tea?  Depends on: 1.volume of tea 2.temperature of tea  We define solubility as being the amount of solute that will dissolve in a solvent at a particular temperature. 11

12. Effect of Temperature on Solubility  Solubility usually increases with higher temperatures.  e.g. at 70 o C, you could dissolve more sugar in tea than you could at 20 o C.  One exception is oxygen in water – less oxygen can be dissolved in hot water than in cold water. 12

13. Solubility Curves  Solubility curves are graphs of solubility vs. temperature.  We plot solubility in g/100g (amount of solute in 100g of solvent) on the y-axis and temperature on the x-axis.  This question comes up a whole lot in exams, learn it really well! 13

14. Solubility Curves  e.g. The table below shows the amount of ammonium chloride that will dissolve in 100 g of water at different temperatures. i.Plot a graph of solubility vs. temperature. ii.Use the graph to estimate the solubility of ammonium chloride at 70 o C. 14 Solubility (g/100g)293746556677 Temperature ( o C)020406080100

15. Crystallisation  Crystallisation is the formation of crystals by cooling a saturated solution.  Since colder solutions can be less saturated, when you cool saturated solutions, some of the solute “undissolves” and forms crystals. 15