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, 4^th 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:

• Identify the unknown compound.  Your compound may be a mixture and thus you must test for all possible cations and anions.
• There is information in your lab manual describing how to test for ions.

 

Requirements for Goal 2:

• To discover as much information about the compound as you can.  Thus, after identifying your unknown, discover as many chemical and physical properties of the compound as you can.

 

Requirements for Goal 3:

• We are going to modify the third goal in the lab manual.  We are going to synthesize calcium carbonate.
• As a group, you will need to synthesize 0.5 g of calcium carbonate be reacting 1 M aqueous solutions of calcium chloride and sodium carbonate.
• Calculate your percent yield and include these calculations in your results and discussion section of your lab report.
• Calcium carbonate is the active ingredient in many antacids.  If one antacid tablet contains 500 mg of calcium carbonate and one bottle contains 150 tablets, how much would it cost to produce the amount of calcium carbonate in one bottle of antacid tablets by reacting calcium chloride with sodium carbonate.  Include these data and calculations in your lab report.
• In the results and discussion section of your lab report, include the complete balanced equation, the complete ionic equation and the net ionic equation for this precipitation reaction.  Be sure to include the physical state of each of the reactants and products.
• Consult a material safety data sheet (MSDS) for each of the reactants and products in this precipitation reaction and find the LD₅₀ or LC₅₀ value for each compound and include it in your report.

 

Requirements for writing your lab report:

• The lab report is an individual project.  Although you collected data in a group, the lab report is an individual project.  Thus each member of the group must generate their own tables and graphs and write their own lab report.
• All lab reports must be typed including all tables.
• All results must be reported in tabular format.  (Use your textbook as a reference to see the proper format for a scientific table.)
• Your lab report will consist of a results and discussion section with data tables and graphs, if appropriate.

 

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:

• Bunsen Burners: The Bunsen burner is a common device used for heating. It is limited in usefulness to warming aqueous solutions or other nonflammable substances. Care must be used when using a Bunsen burner. Your laboratory instructor will demonstrate the proper method for adjusting, lighting, and using a Bunsen burner.
• Wear your safety goggles at all times. You will be using several different acid, base and salt solutions. If you get any solution on you, wash immediately with lots of water.
• Dispose of all waste in the labeled containers in the common equipment area. Use a wash bottle to rinse glassware into the container.
• You will use several different reagents throughout this experiment. Many of the reagents are located in the common reagent area in the front of the lab. When you need a reagent, take it to your lab bench, use it, put the lid back on it and then put it right back. Do not carry open bottles of solutions to the reagent bench (poor etiquette).  Be sure you return it to its proper place.
• Centrifuge safety:  Do not open the centrifuge until it has completely stopped. Do not try to manually stop the centrifuge from spinning. The blank tube filled with water is necessary to balance the instrument.  Do not walk away from a spinning centrifuge.

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.