Qualitative Analysis - Guided Inquiry
Summary
In this inquiry-based experiment, the students design and carry out a sequence of chemical reactions for the separation and identification of iron, silver, and zinc ions in water. Two parallel series of tests will be carried out, one using a known sample containing all three metal cations and the other using unknown samples containing one, two, or all three cations.
CollapseLearning Goals
Concepts:
1. The students will design a qualitative analysis procedure to separate and identify three metal cations from 6 unknown samples.
2. The students will perform a series of precipitation reactions to selectively precipitate the ions out of solution.
3. These complex ion reactions will allow students to positively identify the ions.
4. Upon completion of all analysis reactions, the students will complete a flow-chart that details their analysis and the identification of each ion. The students will also write a formal lab report to report their lab results.
Skills:
The students will accurately keep good records of procedures and observations.
The students will conduct a series of precipitation reactions with accuracy.
The students will complete a formal lab report to summarize all findings.
1. The students will design a qualitative analysis procedure to separate and identify three metal cations from 6 unknown samples.
2. The students will perform a series of precipitation reactions to selectively precipitate the ions out of solution.
3. These complex ion reactions will allow students to positively identify the ions.
4. Upon completion of all analysis reactions, the students will complete a flow-chart that details their analysis and the identification of each ion. The students will also write a formal lab report to report their lab results.
Skills:
The students will accurately keep good records of procedures and observations.
The students will conduct a series of precipitation reactions with accuracy.
The students will complete a formal lab report to summarize all findings.
Context for Use
This activity can really be implemented wherever the instructor wishes. I have used this activity at the end of the school year with my Chemistry students who are 11th and 12th graders. This is a relatively simple inquiry lab that requires limited lab equipment. The solutions are made up in advance and a brief introduction into the use of the reagents is given. At least two lab periods should be scheduled, but I have found that 3 will work the best. Prior to this lab, the students should understand what is happening in a precipitation reaction, but that really is the extent of the prior knowledge.
Description and Teaching Materials
In this experiment, the students will design a qualitative analysis scheme for the separation and identification of three metal cations. The first thing the students will do is complete a series of pre-lab questions in order to review the reactions and what the students might expect to happen. After completing the pre-lab questions, the students will design a procedure to identify the 6 unknown samples. As the students complete their procedures they will make careful observations of the precipitation reactions. Using these observations, the students will construct a flow-chart that tracks the procedures and identifies the metal cations. Upon completion of the flow-chart, the student will write a formal lab report detailing the steps involved in identifying the unknown samples. A series of post-lab questions could also be given to the students to guide their conclusions (I chose not to do this, but have the students draw their own conclusions).
Reference: Chemical Reactions, Flinn ChemTopic Labs, Vol. 6, Cesa, I., Editor; Flinn Scientific Inc. : Batavia, IL (2004)
Reference: Chemical Reactions, Flinn ChemTopic Labs, Vol. 6, Cesa, I., Editor; Flinn Scientific Inc. : Batavia, IL (2004)
Teaching Notes and Tips
3 50-minute lab periods were scheduled for this activity.
Pre-lab questions are intended to provide the students with the background necessary to proceed with designing their procedures. This is an important step in the process of experimental design. After the students have written their procedures, the instructor should review, edit, and approve before the students carry out their plan.
The main goal of this lab is to have the students apply what they have learned about chemical reactions in a practical manner.
Pre-lab questions are intended to provide the students with the background necessary to proceed with designing their procedures. This is an important step in the process of experimental design. After the students have written their procedures, the instructor should review, edit, and approve before the students carry out their plan.
The main goal of this lab is to have the students apply what they have learned about chemical reactions in a practical manner.
Assessment
The assessment will be done with the evaluation of a formal lab report detailing all steps in the experimental design process.
Standards
9-12. I.B. Scientific Inquiry
9-12. II. B. Chemical Reactions
9-12. II. B. Chemical Reactions