Nomenclature — The Ionic Compounds Puzzle
Nomenclature — The Ionic Compounds Puzzle
Purpose
In this experiment you will determine the ratios with which ions combine to form ionic compounds, and to write the corresponding empirical formulas.
Introduction
Ionic compounds consist of positively charged ions (cations) and negatively charged ions (anions) stacked together in an orderly fashion (a crystal!). The empirical formula of the ionic compound, which is the smallest whole number ratio of the ions, depends upon the number of positive charges in the cation, and the number of negative charges in the anion. The ions combine in a ratio that allows all positive charges to balance all negative charges.
This activity will allow you to see the relationship of positive to negative charges in ionic compounds, and how to write empirical formulas for ionic compounds based upon this relationship.
Materials
Be certain that you can identify the equipment and reagents listed below, before starting the experiment.
Scissors, page with cation puzzle pieces, page(s) with anion puzzle pieces, laboratory notebook, or the Ionic Puzzle Answer Sheet
Safety and Waste Management
A large surface area is best for this activity, so it is convenient to work on the laboratory benches. Be certain to clean your workspace carefully, before starting. Safety eyewear is not required for this activity. Scissors can cut skin as well as paper, so be careful.
Clean up all scraps of paper, and return all tools and materials to their assigned locations.
Procedure
1. Cut out the puzzle pieces from the sheets provided. Cut them out quickly — they need not be perfect! There are three or four of each type. Keep each type in a separate stack.
2. Arrange the stacks of cations in alphabetical order in a horizontal line on the lab bench.
3. Arrange the stacks of anions in alphabetical order in a horizontal line on the lab bench.
4. Work through the formulas in the data section, below (or on the answer sheet.) Model the charge balancing by placing the puzzle pieces together such that each positive charge (+) from a cation neighbors a negative charge (-) from an anion. You may need more than one cation and/or anion to achieve this. Every completed ionic compound puzzle will be a rectangle, if you correctly balance charges.
5. Write the formula for each ionic compound by writing the formula for the cation, leaving out the charge, and writing a subscript for the number of cations required for the model, and writing the formula for the anion, leaving out the charge, and writing a subscript for the number of anions required in the model. Use parentheses for polyatomic ions if more than one is needed.
Pre-activity Assignment
Answer the following pre-activity questions. Record your answers in your laboratory notebook or on a blank piece of notebook paper, according to the instructions from your teacher
1. What is an ion?
2. What makes an ion a cation?
3. What makes an ion an anion? (Isn't that a mouthful to say!)
4. What is an empirical formula?
Activity
Use the ion puzzle pieces to make each of the compounds in the table below. Examine the relationship of the number of puzzle pieces of each ion type and how the empirical formula is written. Pay particular attention to the subscripts in the empirical formulas.
| |Compound Name |Empirical Formula |Compound Name |Empirical Formula |
| |sodium chloride |NaCl |aluminum oxide |Al2O3 |
| |sodium oxide |Na2O |magnesium chloride |MgCl |
| |iron(II) oxide |FeO |magnesium nitrite |Mg(NO2)2 |
Record the empirical formula for each compound listed below in your laboratory notebook, or on the report form provided per the instructions of your teacher.
|1) |calcium sulfide |18) |aluminum nitride |35) |Aluminum nitrate | |
|2) |lead(IV) oxide |19) |copper (II) oxide |36) |calcium fluoride | |
|3) |calcium hypochlorite |20) |copper (I) oxide |37) |ammonium sulfate | |
|4) |aluminum oxide |21) |sodium phosphate |38) |ammonium nitrate | |
|5) |iron(II) oxide |22) |calcium nitrate |39) |sodium thiosulfate | |
|6) |magnesium nitrate |23) |calcium sulfide |40) |Aluminum sulfate | |
|7) |sodium nitrate |24) |calcium sulfate |41) |Potassium isocyanate | |
|8) |potassium oxide |25) |lead(II) sulfide |42) |sodium nitrate | |
|9) |sodium fluoride |26) |lead(IV) sulfide |43) |copper(II) acetate | |
|10) |sodium sulfide |27) |lead(IV) phosphate |44) |lithium thiosulfite | |
|11) |magnesium oxide |28) |lead(IV) oxide |45) |iron(III) hydroxide | |
|12) |aluminum chloride |29) |iron(III) oxide |46) |calcium phosphide | |
|13) |aluminum sulfide |30) |iron(II) oxalate |47) |calcium phosphate | |
|14) |potassium cyanate |31) |iron(III) oxalate |48) |ammonium phosphate | |
|15) |magnesium nitride |32) |Potassium phosphate |49) |Potassium iodide | |
|16) |magnesium nitrite |33) |magnesium bromide |50) |sodium cyanide | |
|17) |potassium sulfide |34) |magnesium sulfate | | | |
Post-activity Questions
Answer the following questions either in your laboratory notebook or on the post-activity question sheet supplied according to the instructions from your teacher.
1. What is a monatomic ion? Give three examples.
2. What is a polyatomic ion? Give three examples.
3. What makes ionic compounds charge neutral?
4. What type of solids do ionic compounds make?
5. Why do ionic compounds have empirical formulas and not molecular formulas?
6. Do you expect lead(II) chloride and lead(IV) chloride to have the same chemical properties? Explain.
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