ACP Chemistry Cornerstone ActivityNomenclature — The Ionic Compounds Puzzle

PurposeIn this experiment you will determine the ratios with which ions combine to form ionic compounds, and to write the corresponding empirical formulas.

IntroductionIonic 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.

MaterialsBe certain that you can identify the equipment and reagents listed below, before starting the experiment.

scissors page with cation puzzle pieces page with anion puzzle pieces laboratory notebook, or the Ionic Puzzle Answer Sheet

Procedure1. 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 AssignmentAnswer 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?

ActivityPart A.  Use the ion puzzle pieces to make each of the compounds in the 5 x 5 matrix. 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.  In each box, write the compound name and the empirical formula.

Part A.             anions

cations

F-

fluorideO2-

oxideN3-

nitrideNO3

-

nitrateSO3 2-

sulfite

Na+

sodium

Al3+

aluminum

Pb4+

lead (IV)

Pb2+

lead (II)

NH4+

ammonium

Part B.  Given the names and empirical formulas in the matrix, fill in all of the blank boxes, including ions.Part B. anions

cationsKClpotassium chloride

Ca(C2H3O2)2

calcium acetate

Fe(OH)3

iron (III) hydroxide

FeSO4

iron (II) sulfate

Cu3PO4

copper (I) phosphate

Post-activity QuestionsAnswer the following questions in your lab notebook or on a separate sheet of paper.

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.