Example

1. Reading Solubility Curves Example 50 40 Grams of solute in 100 g of water 30 20 10 5 10 15 20 25 30 35 40 45 50 55 60 Temperature Another way to observe the solubility of a solution is to graph the saturation point at different temperatures Chart G Shows how much solute can be dissolved in 100 g of water At 10oC, 100 g of water can hold 18 g of KNO3 At 20oC, 100 g of water can hold 20 g of KNO3 At 45oC, 100 g of water can hold 80 g of KNO3

2. 50 40 Grams of solute in 100 g of water 30 20 10 5 10 15 20 25 30 35 40 45 50 55 60 Solubility curve Curve showing the maximum amount of solute that can be dissolved in a solvent Each point on the curve represents a saturated solution Temperature Let’s add 30 g of substance X to 100 g of water at 28oC. Find the 28oC mark and the 30 g mark and see where they come together Since this point is on the line, the solution is SATURATED

3. 50 40 Grams of solute in 100 g of water 30 20 10 5 10 15 20 25 30 35 40 45 50 55 60 Temperature Lets add 30 g of X to 100 g of water at 45oC. Can add about 35 g more Unsaturated Find the two points. See how it is below the line? The solution can hold more solute. This is considered Unsaturated Any point below the line is considered unsaturated We can also determine how much more can be added until it is saturated

4. 50 40 Grams of solute in 100 g of water 30 20 10 5 10 15 20 25 30 35 40 45 50 55 60 Temperature Any point that is above the line could indicate one of two things. 1. Supersaturated solution Solvent is holding more solute than it should This only occurs in very few cases, usually we cannot make supersaturated solutions 2. The solution will only dissolve some of the solute. The amount of solute above the line will fall out to the bottom

5. Answers to Example questions (Use the curve from your notes!) Question 1 A. Find the temperature 25oC on the graph, and follow it up until it meets the KNO3 line B. Move across to determine the grams of KNO3 we can dissolve in 100 g of water About 22 g can dissolve

6. Question 2 Use the 30oC point and follow it up to the KNO3 line This indicates we can dissolve about 32 g of KNO3 in 100g of water (Remember, the whole chart is set up for 100 g of water!) Now set up a proportion to determine KNO3 in 50 g of water. 32 . 100 g of water X . 50 g of water = Cross multiply to get about 16 g in 50 g of water

7. Question 3 In this problem, we need to find the amount of water. Using the temperature 35oC, the chart tells us we can dissolve about 42 g of KNO3 in 100 g of water. Now set up a proportion to determine the water needed for 20 g of KNO3 42 g of KNO3. 100 g of water 20g of KNO3 . X = We can cross multiply to get about 47.6 g of water needed.

8. Question 4 From the chart we can determine that at 15oC we can dissolve about 18 g in 100 g of water. Since we are using 200g of water in the question, we can set up a proportion 18 . 100 g of water X . 200 g of water = We can cross multiply to get 36 g of KNO3. Now we need to convert to moles. G = gmm x moles 36 = 101.11 g/ mole x moles Moles = 0.356 moles

9. Question 5 We can use the chart to determine that at 30oC, we can hold about 32 g of KNO3 in 100 g of water. Since we added 50.0 g, the first 32 g will dissolve, the rest will fall to the bottom. 50 – 32 = 18 g will fall out. You may now work on your homework with ONE other person.