Gravimetric Analysis (In Person)
VIDEO LINKS:
Lab Experiments (Write protocols and perform experiments based on these):
- Making a 1 M HCl Solution
- Extracting the Calcium from Chalk
- Making the Saturated Na₂CO₃ Solution
- Precipitating the Calcium from Calcium Chloride
Data analysis and calculations (Use these if you need help with your data and interpretations)
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
- (Existing knowledge, research, and views) Identify the main ingredient in chalk.
- (Representation) Write the balanced chemical equation for the observed reaction between the chalk and the hydrochloric acid.
- (Manipulation) Assuming that your chalk only contains the main ingredient, calculate the volume of the 1 M HCl needed to fully react with it. Show all your work with the appropriate units.
- (Manipulation) Assuming that your chalk only contains the main ingredient, calculate the number of moles of calcium chloride produced in the reaction. Show all your work with the appropriate units.
- (Representation) Write the balanced chemical equation for the reaction that produced the calcium carbonate precipitate.
- (Manipulation) Using the mass of the calcium carbonate precipitate, calculate the mass of the calcium ions in the powdered chalk. (Hint: You will need to use both balanced chemical equations.) Show all your work with the appropriate units.
- (Manipulation) Calculate the percent calcium in chalk. Show all your work with the appropriate units.
- (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 ... |
| There is no calcium in hydrochloric acid. | ||
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. You may use the outline included at the end of this document on how to build your essay to address each category.
- (Existing knowledge, research, and views) Identify the ingredients in chalk.
- (Interpretation) Using your balanced chemical equations that describe the observed reactions, interpret the meaning of each equation on the microscopic and macroscopic scale.
- (Representation) Starting with the molecular equations, derive the total ionic and net ionic equations for each balanced chemical equation.
- (Analysis) Using your balanced chemical equations and your observations, identify the limiting reactant and excess reactant in each reaction.
- (Experiment design) Provide a supported argument for using the sodium carbonate solution to precipitate the calcium and not sodium carbonate powder. (Hint: consider the definition of a precipitation reaction for this answer.)
- (Analysis) If you didn’t have sodium carbonate available, what other compounds could you have used to precipitate the calcium ions? (Hint: consider the solubility table.)
- (Assumptions and Limitations) Describe at least one assumption you made when calculating the amount of calcium from your chalk. Identify at least two reasons from your experiment that make it impossible to determine the exact amount of calcium in the chalk.
- (Analysis) Compare the percent calcium of your chalk with the other groups in the class. Provide at least one argument that explains the similarity and one for the difference.
- (Existing knowledge, research, and views) Calcium carbonate is a white powder, and yet chalk comes in a variety of colors. Describe how colored chalk is made.
- (Existing knowledge, research, and views) Describe the difference between pigments and dyes.
- (Analysis) Predict if adding food coloring to calcium carbonate would result in colored chalk. Provide a supported argument for your choice.
- (Existing knowledge, research, and views) Calcium carbonate is commonly found in nature. List at least 3 materials, beyond chalk that are made of calcium carbonate. Comment on the difference in their properties despite their similar composition.