Solubility
Solubility
Objectives
In this unit, students will explore characteristics of different solutions. They will compare solid and gas solutes in liquid solutions under varying environmental changes (temperature and pressure). Students will also apply a variety of mathematical formulas and graphs to express the concentration levels of different solutions. Students will:
- recognize varying saturation levels.
- use a solubility curve graph to examine varying levels of saturation and solubility present in different solutions.
- compare and contrast the influence of temperature and pressure on different solutions.
- create different types of solutions during a hands-on lab.
- recognize that solutes and solvents are components of a solution.
- compare different methods of expressing the concentration of liquid solutions (percent composition, molarity, and molality).
Essential Questions
Related Unit and Lesson Plans
Related Materials & Resources
The possible inclusion of commercial websites below is not an implied endorsement of their products, which are not free, and are not required for this lesson plan.
- Sodium Thiosulfate Lab
http://atlantis.coe.uh.edu/texasipc/units/solution/solutions.pdf
- Sodium Thiosulfate Safety Information
http://cartwright.chem.ox.ac.uk/hsci/chemicals/sodium_thiosulphate.html
- Chemistry in the Community (ChemCom), 4th ed. by the American Chemical Society. W. H. Freeman, 2000.
Formative Assessment
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View
Multiple-Choice Items:
1. Which statement best describes a supersaturated solution?
A
A solution that is able to dissolve more solute at a given temperature
B
A solution with more solute dissolved in the solution than its saturation point allows
C
A solution that has the maximum amount of dissolved solute at a given temperature
D
A solution that has an equal amount of solute and solvent dissolved at a given temperature
Use the graph below to answer questions 2–4.
2. How many grams of KNO3 can dissolve into 100 g H2O at 50°C?
A
75 g
B
80 g
C
85 g
D
90 g
3. Which salt is supersaturated when 10 g are dissolved at 10°C?
A
KlCO3
B
NaCl
C
NaNO3
D
NH3
4. Which salt has a saturation point of 55 g at 20°C in 100 g H2O?
A
KlCO3
B
NaCl
C
NaNO3
D
NH3
5. Which statement best describes the relationship between the solubility of solids in a liquid solution and temperature?
A
As temperature increases, solubility increases.
B
As temperature increases, solubility decreases.
C
As temperature increases, solubility is unaffected.
D
As temperature increases, solubility increases by a factor of 3.
6. What two factors can increase the solubility of a gas in a liquid solution?
A
An increase in temperature and pressure
B
A decrease in temperature and pressure
C
An increase in temperature and a decrease in pressure
D
A decrease in temperature and an increase in pressure
7. What is the formula for the molarity of a solution?
8. A scientist dissolves a type of salt into 100 g of distilled water until no more will dissolve. The scientist looked up the solubility curve for this particular salt and found out 10 g more of the salt was dissolved into the water than the solubility curve suggested was possible. What explanation best explains why the solubility of this solution was greater?
A
The amount of H2O was less than 100 g.
B
The scientist used a different salt by mistake.
C
The water was a higher temperature than the solubility curve suggested.
D
The scientist stirred the mixture, which caused the intermolecular bonds to strengthen between the salt crystals.
9. Which statement best describes the difference between a solution’s molarity and its molality?
A
Molarity is equal to the moles of solute per liter of solvent; molality is equal to the moles of solute per kilogram of solvent.
B
Molarity is equal to the moles of solute per liter of solvent; molality is equal to the moles of solute per kilogram of solution.
C
Molarity is equal to the moles of solute per liter of solution; molality is equal to the moles of solute per kilogram of solvent.
D
Molarity is equal to the moles of solute per liter of solution; molality is equal to the moles of solute per kilogram of solution.
Multiple-Choice Answer Key:
1. B
2. C
3. A
4. D
5. A
6. D
7. B
8. C
9. C
Short-Answer Items:
10. Create a chemical equation representing 8 g of NaCl being dissolved into 100 g of distilled water to create a salt water solution. Label the following on the chemical equation: solute, solvent, solution.
11. What is the prominent gas in soda and what are two ways to increase the solubility of that gas in the soda?
Short-Answer Key and Scoring Rubrics:
10. Create a chemical equation representing 8 g of NaCl being dissolved into 100 g of distilled water to create a salt water solution. Label the following on the chemical equation: solute, solvent, solution.
Points
Description
3
Student completes all three of the objectives for full credit:
- Chemical equation is accurately written as:
NaCl + H2O = salt water
- Units are labeled accurately and the sum of the solution is accurately written as:
8g NaCl + 100 g H2O = 108g of salt water
- Formula is labeled correctly with the provided terms:
8g NaCl (solute) + 100 g H2O (solvent) = 108g of salt water (solution)
2
Student completes two of the objectives.
1
Student completes one of the objectives.
0
Student completes none of the objectives or fails to attempt the task.
11. What is the prominent gas in soda and what are two ways to increase the solubility of that gas in the soda?
Points
Description
2
Student completes both of the objectives for full credit:
- Student identifies carbon dioxide (CO2) as the gas in soda.
- Student identifies a decrease in temperature and an increase in pressure as ways to increase the solubility of the gas in soda.
1
Student either correctly identifies the gas in soda or identifies both ways to increase solubility of gas in soda, but not both.
0
Student completes none of the objectives or fails to attempt the task.
Performance Assessment:
Use the Performance Assessment Lab handout (S-C-9_Performance Assessment Lab and KEY.doc). Prepare the lab ahead of time and hand out copies of the lab sheets to each student.
Safety Note: Goggles, gloves, and aprons must be worn throughout the lab. Please follow your school safety guidelines for handling chemicals.
- Eye contact: Flush the eye with plenty of water. If irritation persists, call for medical help.
- Skin contact: Wash off with water.
- If swallowed: Call for medical help.
Disposal: Small amounts of dilute sodium thiosulfate solution can be flushed down a sink with a large quantity of water, unless local rules prohibit this. Larger amounts of solution or solid should be stored for later disposal. Check local rules before disposing of this chemical.
Source: http://cartwright.chem.ox.ac.uk/hsci/chemicals/sodium_thiosulphate.html
Performance Assessment Scoring Rubric:
See Answer Key in the Performance Assessment Lab (S-C-9_Performance Assessment Lab and KEY.doc).
DRAFT 06/01/2011
