1.11: Experiment 9 - Precipitation
- Page ID
- 291230
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By the end of this lab, students should be able to:
- Describe precipitation reactions from the molecular perspective
- Record detailed observations for a reaction.
- Predict if a precipitate will form when combining two solutions.
- Write molecular, ionic, and net ionic equations for various reactions.
Prior Knowledge:
Introduction
Aqueous solution is any solution where water is present as a solvent. Rain, vinegar, orange juice are all examples of aqueous solutions that you come across in your everyday life. In chemistry, aqueous solution is indicated by adding "(aq)" to the reactant formula. For example, NaCl(aq) present as individual ions Na+ and Cl- dissolved in water. You might have heard that water is the universal solvent, however, water only dissolves substances that are hydrophilic (from the Greek "hydros" - water and "philia" - bonding or friendship). Compounds that do not dissolve in water remain a solid and indicated by "(s)", for example, AgCl(s).
Solubility rules could be useful in our everyday life, but they are also extremely important in medicine. Sometimes doctors prescribe more than one solution to be administered by the intravenous (IV) route. Mixing two solutions that form a precipitate can lead to very serious consequences. For example, magnesium sulfate is used as an electrolyte replenisher or anticonvulsant, calcium chloride is indicated in the immediate treatment of hypocalcemic tetany (abnormally low levels of calcium in the body that cause muscle spasm), and intravenous sodium bicarbonate is a medication primarily used to treat severe metabolic acidosis. But what will happen if you mix them?
Pre-Lab Primer
This pre-lab assignment is an individual assignment to be completed on your own with the help of the links in the document and at the top of this page. All work must be in your own words. Do not copy and paste information from the internet. The assignment will be due 10 minutes before your lab begins. Late work will not be accepted.
The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.
Interactive Element
In-Lab Assignments
Safety if you were to complete this lab in person:
- Obtain and wear goggles and gloves!!!
- Do not ingest any chemicals or inhale the vapors.
- Clean up all spills immediately! If contact with skin, rinse with water for 15 minutes.
- Before proceeding with this or any other experiment, students must sign the chemical lab safety form.
In these assignments, you will look at some aqueous reactions, and record your observations, molecular equation, total ionic equation and net ionic equation. Make sure to write any evidence of a chemical reaction with sufficient detail to help you distinguish between similar precipitation reactions. Don't write “became cloudy” or “white solid”. Indicate if a gel is produced or crystals form, if the solid was powdery, etc. Keep in mind that some reactions will not occur and you should write NR (for No Reaction). You will know that a reaction occurred if a precipitate, a gas, or color change occurred. Heat (whether it was consumed or evolved) can also be an indicator that reaction occurred, but you may not be able to tell in these videos.
Individual Assignment
Part A: Aqueous Reactions Simulation
Your instructor will play a simulation for you during lab and guide you through the questions in the first part of this assignment. You should answer these questions based on what you observe in the simulation. Be as specific as possible in your answers. You MUST use the correct formatting when writing chemical equations and formulas. Use superscripts, subscripts, and parentheses when necessary.
Part B. Predictions using the solubility table
You will be given a document called a "solubility table" like the one below to use to answer the questions in Part B of your assignment. Your instructor will show you how to use this table to predict whether a reaction will form a precipitate or not. You MUST use the correct formatting when writing chemical equations and formulas. Use superscripts, subscripts, and parentheses when necessary.
The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.
Interactive Element
Group Worksheet
Before watching each video, predict the outcome of the reaction (precipitate or no reaction). Then, watch the video with your group and fill out your worksheet with 1) your observations, 2) molecular equation, 3) ionic equation and 4) net ionic equation for each reaction before moving to the next video.
1. Copper(II)* sulfate and sodium phosphate
* The video says Cu2SO4, but the reaction shown in this video is between copper (II) sulfate and sodium phosphate.
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Query \(\PageIndex{2}\) |
2. Cadmium (II) chloride and sodium sulfide
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Query \(\PageIndex{3}\) |
3. Nickel (II) chloride and sodium carbonate
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Query \(\PageIndex{4}\) |
4. Lead (II) nitrate** and sodium sulfide
** The video says Pb2NO3, but the reaction shown is between lead (II) nitrate and sodium sulfide
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Query \(\PageIndex{5}\) |
5. Nickel(II) chloride and sodium phosphate
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Query \(\PageIndex{6}\) |
6. Silver nitrate and sodium carbonate
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Query \(\PageIndex{7}\) |
The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.
Interactive Element
Post-Lab Problem Set
After you have had a chance to work with your group during lab, you will be given the Precipitation Reactions Post-Lab Problem Set. This is an individual assignment that must be completed on your own, and it is based on your Pre-Lab Primer and your In-Lab Assignments. This assignment will be due the day after your lab meets by 5 p.m. For example, if your lab is on Monday, the Post-Lab Problem Set will be due on Tuesday at 5 p.m. No late work is accepted.
The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.
Interactive Element
Contributors and Attributions
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Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry) led the creation of this page for a 5 week summer course.
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Elena Lisitsyna contributed to the creation and implementation of this page, including the generation of the HP5 question modules.
- Mark Baillie coordinated the modifications of this activity for implementation in a 15 week fall course, with the help of Elena Lisitsyna and Karie Sanford.