Project II: Identification, Properties, and Synthesis of an Unknown Ionic Compound
For project II, we will follow the lab Identification, Properties and Synthesis of an Unknown Ionic Compound on page 115 of the Cooperative Chemistry Laboratory Manual, 4th edition with some modifications. Each group will be given an unknown ionic compound. Working together as a group, you must identify the unknown compound and determine as many chemical and physical properties of the compound as you can. The third requirement of the project will be to synthesize an insoluble ionic compound.
Requirements for Goal 1:
Requirements for Goal 2:
Requirements for Goal 3:
Requirements for writing your lab report:
Grading Project II:
· Experimental Plan (10 pts)
· Notebook (10 pts)
o Bound pages, not loose leaf or spiral, etc.
o Descriptive Table of Contents
o Numbered pages
o Include date data was collected
o Raw data recorded
o Procedures and observations recorded
o Written in ink
o Mistakes crossed out appropriately
· Three Weekly Reports (5 pts each)
· Lab Report (30 pts)
o Results and discussion- Your lab instructor will be looking for the following when grading your results and discussion section:
* Identity of unknown compound, including unknown letter or number?
* Is data reported in tables?
* Chemical properties?
* Physical properties?
* Complete balanced equation, the complete ionic equation and the net ionic equation?
* Cost analysis?
* LD50 or LC50 value?
· Peer Evaluation (10 pts)
· Quiz (10 pts)
Background Reading:
Cooperative Chemistry Laboratory Manual
· Bunsen Burner (p. 53)
· Dealing with Unknown Compounds (p. 58-63)
· Filtration (p. 70)
· Identification, Properties and Synthesis of an Unknown Ionic Compound (p. 115)
Chemistry & Chemical Reactivity
· Chemical Reactions (sections 3.1, 3.2, 3.4-3.6, Reactions of Acids & Bases)
· Ionic Compounds (section 2.7)
Chemical Principles, The Quest for Insight
· Chemical Equations (F61-F64)
· Compounds, Ionic Compounds (F23, F25-F28)
· Precipitation Reactions (F67-F70)
· Qualitative Analysis (475-477)
Additional Background Information: Chemical analysis can be divided according to quantitative analysis and qualitative analysis. In the last experiment, we were asked to quantitatively find the density of various materials. However, sometimes a chemist is interested in what species are present in a sample, as opposed to the amount of species present in a sample. Thus, a qualitative analysis involves the determination of the types (not amounts) of ions present in a solution. A "qualitative analysis scheme" is then a systematic procedure for separating and identifying various ions present in an aqueous solution.
The procedures in most qualitative analysis experiments involve the use of using precipitation reactions. A precipitation reaction is a reaction in which an insoluble solid compound is formed when solutions of two soluble compounds are mixed. The solid compound that forms during a precipitation reaction is referred to as the precipitate. An example of a precipitation reaction is the reaction between aqueous solutions of KI and Pb(NO3)2:
2KI (aq) + Pb(NO3)2 (aq) ® PbI2 (s) + 2KNO3 (aq)
We know that the ionic compounds KI, Pb(NO3)2, and KNO3 are soluble in water and PbI2 is not soluble in water, see "General Solubility Guidelines of Ionic Compounds in Water" on page 60 of the Cooperative Chemistry Laboratory Manual.
There are some general procedures in qualitative analysis that will be used throughout this experiment. One is the use of a centrifuge to aid the separation of a precipitate from a solution in a test tube. There is a centrifuge at the end of each lab bench. To use the centrifuge, make sure the test tube containing the precipitate and solution (sample test tube) is not overly full. Place the sample test tube in one of the centrifuge tubes. Place a blank tube containing the same amount of water as you have in your sample test tube in the centrifuge tube that is opposite your sample test tube. Turn on the centrifuge and allow it spin for about 1 minute. Once you have centrifuged your sample test tube, now you can decant the supernatant liquid from the precipitate. Simply pour off (decant) the liquid that is above the precipitate (the supernatant).
Safety Precautions:
Qualitative Procedure for the Analysis of Ca2+ and Mg2+ Ions
1. Obtain 1 mL (approximately 20 drops) of the solution to be analyzed in a small test tube.
2. Add 2 drops of 6M HNO3 and then add 1 mL of 6M NH4OH.
3. Add 1 mL of 0.3 M (NH4)2CO3 and stir. If a precipitate forms, Ca+2 ions are present. Centrifuge and decant the supernatant, which may contain Mg+2. Save this solution for analysis in step 4. If no precipitate forms upon the addition of the 0.3 M (NH4)2CO3, Ca2+ are not present and you should continue with step 4.
4. To the solution from step 3, add 1mL of K2HPO4 solution, stir and let stand 1 minute. The slow formation of a white precipitate indicates magnesium.