Chemistry Lab Dissociation-Observing an Ionic Reaction

Chemistry Lab Dissociation-Observing an Ionic Reaction

A teaspoon of salt is added to a glass of water and the crystals disappear. A factory discharges waste containing mercury salts into a river, contaminating an entire fishing industry. Ironically, even though these are very common events, the actual process of how a solid dissociates or dissolves remains one of the least understood processes in science. However, it is known that many dissolving crystals form ions that migrate and diffuse in a suitable liquid medium. These released ions can then recombine by attracting other oppositely charged ions to them. If the solubility of this newly formed compound is very low, the result is that a precipitate forms. It can be said that an ionic reaction has taken place.

In this investigation, you will observe reactions very closely and will be able to watch actual precipitates form.

Purpose

To observe the mechanics of dissociation and double replacement reactions

To predict products and solubility for double replacement reactions

To interpret an ionic reaction by drawing a series of pictures.

Materials

Apparatus

  Petri dish with cover

  2 scoopulas

  Distilled water

Reagents

  Copper (I) chloride crystals CuCl

  Potassium iodide crystals KI

  Calcium chloride crystals CaCl2

  Sodium carbonate crystals Na2CO3

  Copper (II) nitrate crystals Cu(NO3)2

Procedure

1.  Put on your safety goggles, laboratory apron.

PART ONE

2.  Open a Petri dish and ½ fill both halves with distilled water. Place them on the lab bench and allow the water to settle for a minute or two.

3.  One lab partner should have a scoopula with one or two crystals of potassium iodide KI, and the other partner should have a scoopula with one or two crystals of copper (I) chloride CuCl. Carefully add the crystals to the water on opposite sides of the Petri dish. (Teacher may do this step)

4.  Make as many observations as possible for the next five minutes. In Table 1, draw submicroscopic pictures of what you think happened. Using colors for the different ions present might be helpful. You may also take pictures!!

PART TWO

5.  Add distilled water to the second Petri dish and allow it to stand for one or two minutes. Now add one or two small sodium carbonate Na2CO3 crystals to the top of the dish (twelve o’clock position). As soon as possible, add crystals of copper (II) nitrate Cu(NO3)2 and calcium chloride CaCl2 to the dish, equidistant from the sodium carbonate (that is, at the four o’clock and eight o’clock positions). (Teacher may do this step)

6.  Repeat Step 4 for these reactions. Use Table 2 to record observations.

7.  Before you leave the laboratory, wash your hands thoroughly with soap and water.

Data Presentation

TABLE 1. Potassium Iodide KI and Copper (I) Chloride CuCl

TABLE 2. Sodium Carbonate Na2CO3 , Calcium Chloride CaCl2 , and Copper (II) Nitrate Cu(NO3)2

Data Analysis

1.  From Table 1, write the chemical equation and predict the solubility for the chemical reaction of potassium iodide KI and copper (I) chloride CuCl.

2.  From Table 2, write all three equations and predict the solubility for the possible ionic chemical reactions.

Conclusions

1)  Using the observations from Table 2, propose which possible chemical reaction did not occur and explain why. (Hint: think about solubility of double replacement reactions)

2)  Define dissociation and explain its role in the chemical reactions that were observed.