1. Reading Solubility Curves
Introduction Notes and Example Problems

2. What is Solubility?
The maximum amount of a substance that will dissolve in a certain amount of solvent at a given temperature
Example: The solubility of salt is 50 grams of salt (NaCl) in 100 g of water at 20˚C.
RECALL:
Solute = is the substance that is dissolved
Solvent = does the dissolving, dissolves the solute

3. READING THE GRAPH To read the graph, find the line for the substance
READING THE GRAPH To read the graph, find the line for the substance. The amount that dissolves at a given temperature is on the y-axis.

4. Temperature and Solubility
The temperature of the solution affects how much of the solute is dissolved by the solvent.
Increasing the temperature does not always increase the solubility.
Solubility curves are used to show how the solubility of a substance changes with temperature.

5. EX.1 How much KNO3 dissolves in 100g H2O at 50oC?
First double check the amount of water matches the graph you are using. This one does (100 g of water).
Find the substance line.
Find the temperature and follow up to the substance line. (green)
Read across to the y-axis and this is the answer. (blue)
Since it between 80 and 90, you will need to estimate your answer. Around 83 grams.
YOUR TURN!

6. EX.2 How many grams of NaNO3 will dissolve in 60 mL of H2O at 10oC?
First double check the amount of water matches the graph you are using. This one does NOT. That means we’re going to have to set up a proportion.
Find the substance line.
Find the temperature and follow up to the substance line. (green)
Read across to the y-axis. (blue) 81 grams
This is how much that can dissolve in 100 g or mL of water. Set up a proportion (see below) and solve for x.
x=(81 x 60)/100 =48.6 g NaNO3
YOUR TURN!

7. Saturation TERMS: RECALL:
saturated solution-means it is full of solute, can’t hold any more solute or no more solute will dissolve.
unsaturated solution-means it can hold more solute, it is not full or more solute will dissolve
NEW TERM:
supersaturated solution-this solution has been tricked to hold more solute than it can typically hold, this is done by extreme heating and then cooling it down, if one more grain of solute is put in, all the extra solute that was put in will come out.
CHECK IT OUT

8. Saturation Calculations
You can tell which type of solution you have based on where the amount compares to the solubility curve line.
Saturated- the amount will be right on the solubility curve line
Unsaturated-the amount will be below the solubility curve line
Supersaturated-the amount will be above the solubility curve line

9. EX. 3 If you have 40 g of KCl in 100 mL of water at 80oC
EX.3 If you have 40 g of KCl in 100 mL of water at 80oC. Identify the type of solution.
First double check the amount of water matches the graph you are using. This one does (100 g of water).
Find the substance line.
Find the temperature and follow up to the substance line. (green)
Find the amount on the y-axis (blue) and bring it over to the temperature line .
Notice it is below the solubility curve of KCl. At this temperature I should be able to dissolve around 50 grams of KCl in 100 g of water.
Because the intersection is BELOW THE KCl LINE I have a UNSATURATED SOLUTION. I would be able to dissolve more if needed.
ONE MORE EXAMPLE

10. EX. 3 If you have 130 g of KNO3 in 100 mL of water at 60oC
EX.3 If you have 130 g of KNO3 in 100 mL of water at 60oC. Identify the type of solution.
First double check the amount of water matches the graph you are using. This one does (100 g of water).
Find the substance line.
Find the temperature and follow up to the substance line. (green)
Find the amount on the y-axis (blue) and bring it over to the temperature line .
Notice it is above the solubility curve of KNO3. At this temperature I should only be able to dissolve around 102 grams of KNO3 in 100 g of water.
Because the intersection would be ABOVE THE KNO3 LINE I have a SUPER SATURATED SOLUTION.
ON YOUR OWN!