Solutions and Colligative Properties (Remote)
VIDEO LINKS:
Lab Experiments (Write protocols and perform experiments based on these):
- Weighing:
- Making the molar solution:
- Making the molal solution:
- Preparing the liquids:
- Determining the freezing point:
- Determining the melting point:
Data analysis and calculations (Use these if you need help with your data and calculations)
- Beginning Solutions:
- Expressing Concentrations:
- Concentration Unit Interconversion:
- Freezing Point Depression:
The prelab must include Experimental Protocol, Chemical Table and Equipment Table.
The lab report requires all sections (including prelab sections) to be completed in one document.
Experimental Protocol
(Analysis) Watch the experiment videos. Take notes on the protocol. Stop the video and re-watch as necessary to acquire the details of the procedure. Write out the protocol for each part of the experiment. (It can be written in sequential steps. Complete sentences are not necessary.) This is the protocol you will follow, so be detailed.
Chemical Table
(Representation) Prepare your chemical table including the materials you will use in the experiment. Here is a general template that you may use.
| Chemical Name | Chemical Formula | Molar Mass (g/mol) | Hazards | Reference | PPE |
| Sodium Chloride | NaCl | 58.5 | Skin irritation | https://fscimage.fishersci.com/msds/21105.htm | |
Equipment Table
(Analysis) Identify the equipment (type AND size) needed for the experiment and include the name and an image of each. Be sure to describe the equipment, how to use it, and why it is suitable for this use.
| Equipment Name | Equipment Picture | Intended Purpose |
Data Collection
(Acquiring competencies) Following your detailed protocol based on the videos, perform all the experiments. Record your observations and take pictures of your key steps in the process. Your observations and images need to be incorporated in your data section and this section should be as detailed as possible as you will use this information to complete your discussion.
Data Processing
- (Manipulation) Calculate the molarity of a 5%vinegar solution.
- (Manipulation) Calculate the molality of a 5%vinegar solution.
- (Manipulation) Calculate the mole fraction of a 5%vinegar solution.
- (Existing knowledge, research and views) Find and list the molarity, molality and mole fraction of the 5% white vinegar solution using the published literature. Include your reference.
- (Manipulation) Calculate the molarity of a 5% NaCl solution.
- (Manipulation) Calculate the molality of a 5% NaCl solution.
- (Manipulation) Calculate the mole fraction of a 5% NaCl solution.
- (Analysis) Compare the molarity, molality and mole fraction values for the 5% vinegar solution and the 5% NaCl solution. Provide at least one supported argument for any observed differences.
- (Manipulation) Calculate the freezing point depression for 5% vinegar solution.
- (Manipulation) Calculate the freezing point of the 5% vinegar solution.
- (Manipulation) Assuming that your calculated freezing point for the 5% vinegar is the true value, and the measured temperature is the experimental value, calculate the percent error of your experiment.
- (Manipulation) Calculate the freezing point depression for the 5% NaCl solution.
- (Manipulation) Calculate the freezing point of the 5% NaCl solution.
- (Manipulation) Assuming that your calculated freezing point for the 5% NaCl is the true value, calculate the percent error of your experiment.
- (Representation) Draw the heating curve for the freezing of the three liquids. Identify each curve either with a different color or other identifier.
- (Representation) Draw the heating curve for the melting of the three frozen liquids. Identify each curve either with a different color or other identifier.
- (Assumptions and Analysis) Fill in the following table using the observations and data from your experiments.
| Assumptions made | Testing the assumption | If assumptions are wrong ... |
| Acetic acid does not ionize in water. | Compare the freezing point of the solution with the freezing point of a nonelectrolyte of identical molality. | Changes will be apparent. |
| Distilled water is pure. | The freezing point will be 0.00 °C. | |
Discussion
Write a minimum one-page (12 font, single spaced) discussion on the experiment conducted this week. Address at least one question in each category as fully as possible integrating the collected data, providing explanations for the observed trends, and evaluating whether your original assumptions about the experiment were validated by the results. The assignment will be graded on completeness, clarity of the explanations and the meaningful integration of the collected and calculated data. Correct grammar and appropriate format for the chemical formulae and chemical reactions is expected.
- (Existing knowledge, research and views) Define molarity, molality, mass percent and mole fraction.
- (Acquiring competencies) Identify the appropriate glassware needed to make molar vs molal solutions and describe the purpose of both.
- (Existing knowledge, research and views) Define the freezing point; and describe the properties of the solvent that will contribute the most to the freezing point.
- (Existing knowledge, research and views) Define the freezing point constant and describe how its value is found.
- (Existing knowledge, research and views) Define aqueous solutions and describe what kind of solutes can be used to prepare them. (Hint: address both molecular and ionic compounds)
- (Representation) Classify the chemicals used in this experiment as strong, weak or nonelectrolytes and describe what happens to the chemicals when dissolved in water using the appropriate chemical equations. (Hint: your equation may have a single or a double arrow)
- (Analysis) Describe how the amount and nature (ionic or molecular) of the solute influences the freezing point depression.
- (Existing knowledge, research and views) Define molality. Provide at least one supported argument for why this unit of concentration is more appropriate for this experiment compared to others, such as molarity.
- (Analysis) Identify at least one reason for why the freezing point depression of materials with similar molar masses may be different. Provide at least one supported argument for your choice.
- (Analysis) Compare the freezing point depression values of the 5% vinegar and 5% NaCl solution and provide at least two supported arguments for the difference.
- (Assumptions) Describe at least one assumption that you made when you selected an i value of 2 for salt and an i value of 1 for vinegar.
- (Analysis) Compare the same freezing points from your team. Discuss the accuracy and precision of the experiment.
- (Existing knowledge, research and views) If you lived in an area where it snowed, what would be put on the roads and sidewalks to keep people safe? Provide a supported argument for why that choice is preferable over NaCl
- (Experiment design) Propose a protocol for testing boiling point elevation that is similar to the freezing point depression experiment that you just did.
Recommended Discussion Outline:
Concentration can be expressed in multiple ways. The main four are: …..
Colligative properties are …. In this experiment we studied …. which uses …. as the most useful form of concentration, because …..
Materials based on their interaction with water can be classified as: ….. In our experiment, vinegar is …. and salt is …. This classification is useful for colligative properties because …..
Acetic acid and salt are similar in …. and they are different in …. This results in …. as observed in our experiment ….
Freezing and melting are ….. Consequently, freezing point is … and it is …. as the melting point.
The freezing point constant is …. and depends on …. In our experiment, the freezing point constant was ….
Some practical applications of colligative properties are …..