Which chemical(s) in this lab is/are considered corrosive? If a chemical gets in your eye, what is the proper response? What should be done with the waste generated in this lab
Experiment 1 and 2
Qualitative Analysis
PURPOSE
To develop a separation scheme and confirmatory tests for Fe3+, Ba2+, and Ag+ cations, and to use it to identify the ions in a sample of unknown composition.
GOALS
- To explore solubilities and reactivities of different metal ions.
- To identify ions present in unknown solutions using "separation methods."
- To gain experience with logically developing a qualitative analysis scheme.
INTRODUCTION
Qualitative analysis is the process by which components of mixtures are separated and identified. Unlike quantitative analysis, where the amount of a particular material is measured, a qualitative analysis scheme simply confirms the presence or absence of certain materials. A common analysis is the identification of aqueous ions. In such an analysis, there are two distinct phases. First, a scheme must be developed to separate the ions from each other. Then, a different test is performed to uniquely confirm the identity of each separated ion. In this lab, we develop a qualitative analysis scheme to separate and identify the components of a chemical mixture. The mixture will be composed of the iron (III) ion (Fe3+), the barium ion (Ba2+), and the silver ion (Ag+).
In addition to analyzing the unknown for its component ions, the development of a qualitative analysis scheme highlights some of the important chemical behavior of these metal salts in aqueous solution. The principles of
Ions are often separated in solution by their different solubilities. A metal ion in a mixture may precipitate (form a solid) in the presence of a specific anion, while the remaining metal ions remain dissolved (in aqueous form). The two ions may be separated by collecting the solid at the bottom of a test tube in a centrifuge, a device that creates a centrifugal force by rotation. After the precipitate is compacted, the supernatant (the liquid solution above the solid) is decanted (carefully poured off) into a separate container. The soluble ion is in the liquid supernatant while the insoluble ion is in the solid precipitate. Thus they are physically separated from each other when the liquid is poured off, leaving the solid behind. The solid precipitate is typically washed with water to help remove any traces of the soluble ions that remain. This prevents "false positive" test results later on.
Once the ions in a mixture have been separated, their identity can be further verified by a confirmatory test. In a confirmatory test, each ion has a unique response to an added chemical, such as a solution color change or the formation of a precipitate. This unique response confirms the presence of that particular ion.
PRELAB Questions
Name: ___________________________________________ Date Performed: _________________
Year and Section: _________________________________ Date Submitted: __________________
- Which chemical(s) in this lab is/are considered corrosive?
- If a chemical gets in your eye, what is the proper response?
- What should be done with the waste generated in this lab
- Which ions are being separated in this qualitative analysis scheme?
- Which of these ions may affect your skin and what is the effect?
- Define the following terms.
- supernatant
- precipitate
- decant
- What safety practices should be followed when centrifuging?
POST-LAB Questions
Name: ___________________________________________ Date Performed: __________________
Year and Section: _________________________________ Date Submitted: __________________
- Question 1:Which ion(s) precipitate when HCl is added?
- Question 2:Which ion(s) precipitate when H2SO4 is added?
- Question 3a:Based upon your observations from Part A, which ion(s) precipitate when HCl is added?
Question 3b: Which ions(s) remain in the supernatant?
- Question 4a:Based upon the solubility rules in the introduction, which ion(s) remaining in the supernatant from step 4 will precipitate in basic solution?
Question 4b: Which ion(s) remain in the supernatant from step 5?
- Question 5a:Based upon your observations in Part A and logic, which ion(s) remaining in the supernatant from step 6 will precipitate when H2SO4 is added?
Question 5b: Which ion(s) remain in the supernatant from step 7?
- Question 6:Use the data you have acquired in Parts A and B to complete the flow chart below. It will serve as a reference for identifying the cations in an unknown solution in Part C.
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