Materials Included In Kit

Additional Materials Required

Prelab Preparation

This procedure only needs to be done by the teacher or the first lab group. The labeled pipets may then be stored in the pipet holders (cassette cases) for later labs and may be refilled as necessary. It is best to store the pipets empty and refill them just prior to lab. Be sure to fill the pipets with the correct solutions; always carefully check the labels on the pipets and to avoid accidental contamination.

1. Gather 14 Beral-type pipets and 14 blank labels.
2. Using waterproof ink or a pencil, write the formulas for the 14 solutions listed in the Materials section above. Write on only one-half of the label since the label will be folded in half around the pipet stem. Note: There will be two pipets for lead nitrate since it is used in both Parts I and II.
3. Fold the labels in half around the pipet stem just above the bulb (with the bulb facing downward and the tip pointed upward).
4. Label two pipet (cassette) holders. For the Part I pipet holder, make a label that says “Part I Solutions” and for the Part II pipet holder, make a label that says “Part II Solutions.”
5. Place the seven labeled pipets for Part I in the Part I pipet holder; place the seven labeled pipets for Part II in the Part II pipet holder (see Figure 1).
   {11826_Procedure_Figure_1}

Safety Precautions

Barium chloride, lead nitrate and sodium chromate solutions are toxic by ingestion. Silver nitrate solution is toxic, corrosive, light-sensitive and stains skin and clothing. Sodium hydroxide solution is corrosive and a body tissue irritant. Avoid all eye and body tissue contact with all solutions. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulation that may apply, before proceeding. Any wells that contain reactions which contain lead or chromate salts must be must be disposed of according to Flinn Suggested Disposal Method #27f. The lead nitrate solution may be disposed of according to Flinn Suggested Disposal Method #27f. The silver nitrate solution may be disposed of according to Flinn Suggested Disposal Method #11. Any wells that contain barium compounds must be disposed of by converting it to insoluble barium sulfate according to Flinn Suggested Disposal Method #27h. Remaining amounts of the reagents included in the kit may be stored for future use or disposed of according to the specific method designated on their chemical label.

Lab Hints

Suggested Guide for Analysis of the Substances and the Development of General Solubility Rules

Part III—Making a List of Soluble, Insoluble and Unknown Substances

1. In each circle where a reaction was performed of Data Tables 1 and 2, write the formulas for the two possible double replacement products. This should be done even for those combinations that produced no reaction.
2. Use Table 3 to make a list of all the substances that you know to be soluble in water. Generate this list of soluble substances in two ways.
   1. Write down each solution that you used in this experiment from the materials list. (Since these are all solutions with no precipitates, you can assume they are all soluble.)
   2. Look at your recorded observations in the data tables. For each reaction that did not produce a precipitate (NR), four substances are now known to be soluble—the two starting substances and the two possible products. For example, when mixing two soluble substances, such as sodium carbonate and ammonium sulfate, no reaction occurs. This tells you that sodium sulfate and ammonium carbonate are also soluble.
3. Generate a list of all substances that you know to be insoluble. Look at your data tables. Examine each of the reactions that did produce a precipitate. Each pair of solutions mixed together can produce two new possible substances, as discussed in the background. Make the assumption that if a precipitate is formed when mixing two solutions, the precipitate is formed by only one of the two new substances. Compare each of the new substances to the list of soluble substances. If one of the new substances appears on the soluble list, the other must be the precipitate and can be added to the insoluble column. If neither one of the new substances appears on the soluble list, then place both substances in the unknown column. Write the two substances together as a pair. This way, later you will know that if one substance is found to be soluble, the other must be insoluble.
4. Look at your lists of soluble and insoluble substances. Cross out any duplicate entries. Leave the list of unknown substances unchanged.
5. On a second copy of Table 3, categorize and alphabetize columns 1 and 2 by the anionic part (second word) of the salt. For example, potassium chloride would be listed as “Chloride, potassium” and would be grouped with all other chlorides in that column. Leave column 3 (unknown substances) as is, with the salts written in pairs. Do not mix up the pairs.

Part IV—Analyzing the Solubility List and Developing General Solubility Rules

6. Examine the pairs of substances in the unknown column of Table 3. Remember, if one substance is found to be soluble, the other must be insoluble. Look for any substances that can now be definitely determined to be soluble or insoluble. Write these in the appropriate column of Table 3.
7. Look for any common relationships among the substances in the unknown column and that of the soluble or insoluble substances. The key objective at this point is to remove all of the substances from the unknown column and place them in either the soluble or the insoluble column using logic and the process of elimination. There will be a point where no more substances can be moved from the unknown column by simply looking at laboratory data. At this point, some inferences and generalizations will need to be made. For example, are most (or all) of the nitrate compounds in the same column? How about the ammonium or potassium compounds? Use the categories in Table 4 to help with this step.
8. After completely eliminating the unknown column, examine the substances in the soluble and insoluble columns. Each column should be organized by group (e.g., carbonates, chlorides). Fill in Table 4 with the solubility of each group, including any exceptions that you observe.

Teacher Tips

• The first class that performs this lab will prepare the labels and pipets to be used by the rest of the classes who perform the lab.
• There are 210 pipets (14 pipets per group x 15 groups) included in the kit.
• There are 240 labels included in the kit. Use the 30 extra labels to label the pipet (cassette) holders with “Part I Reactions” or “Part II Reactions.” Be sure to use waterproof ink or pencil on the labels.
• Remind students to hold the pipets vertically when dropping to produce uniformly-sized drops.
• To store the labeled pipets in the pipet holders (cassette cases), cut off the ends of the pipet barrels. You may want to store the pipets empty and then refill them with solution when preparing for the next lab. Note: To fill the pipets once the tips are cut off, pour the solutions into labeled beakers since the pipet will not reach into a reagent bottle.
• Provide two copies each of Tables 3 and 4 to each student. The first copy should be used as a preliminary list; the second as an alphabetized and categorized list.
• Students may need some guidance during the data analysis part. Guide students to look for patterns. For example, there are no ammonium, potassium, sodium or nitrate compounds in the insoluble column.

Sample Data

References

Ciardullo, C. V. Micro Action Chemistry, Vol. 2; Flinn Scientific: Batavia, IL, 1992; pp 49–53.

Introduction

Discover some general rules of solubility for ionic substances. Conduct 42 chemical reactions, determine the solubility of the products, analyze the patterns and formulate the rules.

Concepts

• Precipitation reactions
• Solubility rules

Background

An ionic salt is a compound composed of two parts—cations (positively charged ions) and anions (negatively charged ions). When an ionic salt is dissolved in water, the salt crystal dissociates or separates into its corresponding cations and anions. For example, potassium iodide (KI) dissociates into potassium cations (K⁺) and iodide anions (I^–) according to Equation 1:

Similarly, the ionic salt lead nitrate [Pb(NO₃)₂] dissociates into lead cations (Pb²⁺) and nitrate anions (NO₃^–) according to Equation 2: When two ionic salts are mixed together in water, two new combinations of cations and anions are possible. In some cases, the cation from one salt and the anion from the other salt may combine to form an insoluble solid product, which is called a precipitate. For example, if solutions of potassium iodide and lead nitrate are mixed together, a solid precipitate of lead iodide (PbI₂) forms, as shown in Equation 3: Notice that the potassium cations (K⁺) and nitrate anions (NO₃^–) remain dissolved in solution. They do not combine to form a precipitate and thus do not participate in the reaction. These ions are referred to as spectator ions. Spectator ions do not participate in the overall reaction (hence the term spectators) and are often omitted from the net ionic equation. A net ionic equation is one that includes only the ions participating in the reaction. Thus, Equation 3 can be reduced to Equation 4: The example described above shows that a precipitate of PbI₂ forms when a solution of KI is mixed with a solution of Pb(NO₃)₂. However, when two salt solutions are mixed together and no visible precipitate forms (indicating that no reaction occurs), it can be concluded that all combinations of the cations and anions from the two salt solutions are soluble in water.

It must be noted that every salt has some degree of solubility. Some salts dissolve readily in water while others will not. Even if a salt is considered insoluble (forming a solid precipitate), there is still some small amount of that salt dissolved in the water. Tables of solubilities are available to predict whether or not a precipitate will form when two salts are mixed together. However, observing precipitation reactions in a laboratory setting and becoming familiar with the general rules of solubility can be extremely valuable.

In this laboratory experiment, 14 salt solutions will be combined, two at a time—seven in Part I and seven in Part II—totaling 42 chemical reactions. Observations will be recorded as to which combinations form a precipitate and which do not undergo a reaction. From these results, a list of soluble substances and a list of insoluble substances will be generated. This list will be analyzed and some general rules of solubility will then be developed.

Materials

Safety Precautions

Barium chloride, lead nitrate and sodium chromate solutions are toxic by ingestion. Silver nitrate solution is toxic, corrosive, light-sensitive and stains skin and clothing. Sodium hydroxide solution is corrosive and a body tissue irritant. Avoid all eye and body tissue contact with all solutions. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

Part I—Mixing Pairs of Solutions in Data Table 1

1. Take the pipet holder with the 7 labeled pipets for Part I to the stock solutions table. Fill (about halfway) the 7 pipets with the appropriate solutions and take them back to your lab bench.
2. Place a 48-well reaction plate on top of a black table or black piece of paper as shown in Data Table 1.
3. Using Data Table 1 as a guide, place 4 drops of silver nitrate solution, AgNO₃, into well A1. Be sure to hold the pipet vertically for uniformly sized drops. Continue adding 4 drops of AgNO₃ solution to each well down the vertical column 1, wells B1 through F1.
4. Fill each vertical column with 4 drops of each solution as follows:

   • Place 4 drops of BaCl₂ solution into wells B2–F2.

   • Place 4 drops of Na₂CO₃ solution into wells C3–F3.

   • Place 4 drops of (NH₄)₂SO₄ solution into wells D4–F4.

   • Place 4 drops of Pb(NO₃)₂ solution into wells E5–F5.

   • Place 4 drops of Ca(NO₃)₂ solution into well F6.

5. Now add 4 drops of BaCl₂ solution to the solution already in well A1. Record your observations immediately. (Note: If a precipitate appears, write “PPT” in the correct circle of Data Table 1. Record the color of the precipitate. If no precipitate appears to have formed, write “NR” for No Reaction in the correct circle of Data Table 1. Make sure to leave space in the circles to also write the two possible products of the reactions.)
6. Continue the process of mixing solutions by adding 4 drops of each of the solutions listed along the left side of Data Table 1 to the correct well. Record your observations immediately, as described in step 5.
7. Once Data Table 1 is completed, immediately flush the reaction plate with tap water. The solutions may be rinsed down the drain with plenty of water. Rinse the well plate with distilled water and tap it on a paper towel to dry it out—your plate is now ready for Part II.

Part II—Mixing Pairs of Solutions in Data Table 2.

8. Take the pipet holder with the 7 labeled pipets for Part II to the stock solutions table. Fill (about halfway) the 7 pipets with the appropriate solutions and take them back to your lab bench.
9. Place a 48-well reaction plate on top of a black table or black piece of paper as shown in Data Table 2.
10. Using Data Table 2 as a guide, place 4 drops of iron(III) chloride solution, FeCl₃, into well A1. Be sure to hold the pipet vertically for uniformly-sized drops. Continue adding 4 drops of FeCl₃ solution to each well down the vertical column 1, wells B1 through F1.
11. Fill each vertical column with 4 drops of each solution as follows:

    • Place 4 drops of NaOH solution into wells B2–F2.

    • Place 4 drops of MgBr₂ solution into wells C3–F3.

    • Place 4 drops of K₂CO₃ solution into wells D4–F4.

    • Place 4 drops of Pb(NO₃)₂ solution into wells E5–F5.

    • Place 4 drops of Na₂SO₄ solution into well F6.

12. Now add 4 drops of NaOH solution to the solution in well A1. Record your observations immediately. Note: If a precipitate appears, write “PPT” in the correct circle of Data Table 2. Record the color of the precipitate. If no precipitate appears to have formed, write “NR” for No Reaction in the correct circle of Data Table 2. Make sure to leave space in the circles to also write the two possible products of the reaction.
13. Continue the process of mixing solutions by adding 4 drops of each of the solutions listed along the left side of Data Table 2 to the correct well. Record your observations immediately, as described in step 12.
14. Once Data Table 2 is completed, immediately flush the reaction plate with tap water. The solutions may be rinsed down the drain with plenty of water. Rinse the well plate with distilled water and tap it on a paper towel to dry it out.

Part III—Making a List of Soluble, Insoluble and Unknown Substances

1. In each circle where a reaction was performed of Data Tables 1 and 2, write the formulas for the two possible double replacement products. This should be done even for those combinations that produced no reaction.
2. Use Table 3 to make a list of all the substances that you know to be soluble in water. Generate this list of soluble substances in two ways.
   1. Write down each solution that you used in this experiment from the materials list. (Since these are all solutions with no precipitates, you can assume they are all soluble.)
   2. Look at your recorded observations in the data tables. For each reaction that did not produce a precipitate (NR), four substances are now known to be soluble—the two starting substances and the two possible products. For example, when mixing two soluble substances, such as sodium carbonate and ammonium sulfate, no reaction occurs. This tells you that sodium sulfate and ammonium carbonate are also soluble.
3. Generate a list of all substances that you know to be insoluble. Look at your data tables. Examine each of the reactions that did produce a precipitate. Each pair of solutions mixed together can produce 2 new possible substances, as discussed in the background. Make the assumption that if a precipitate is formed when mixing two solutions, the precipitate is formed by only 1 of the 2 new substances. Compare each of the new substances to the list of soluble substances. If one of the new substances appears on the soluble list, the other must be the precipitate and can be added to the insoluble column. If neither one of the new substances appears on the soluble list, then place both substances in the unknown column. Write the two substances together as a pair. This way, later you will know that if one substance is found to be soluble, the other must be insoluble.
4. Look at your lists of soluble and insoluble substances. Cross out any duplicate entries. Leave the list of unknown substances unchanged.
5. On a second copy of Table 3, categorize and alphabetize columns 1 and 2 by the anionic part (second word) of the salt. For example, potassium chloride would be listed as “Chloride, potassium” and would be grouped with all other chlorides in that column. Leave column 3 (unknown substances) as is, with the salts written in pairs. Do not mix up the pairs.

Part IV—Analyzing the Solubility List and Developing General Solubility Rules

6. Examine the pairs of substances in the unknown column of Table 3. Remember, if one substance is found to be soluble, the other must be insoluble. Look for any substances that can now be definitely determined to be soluble or insoluble. Write these in the appropriate column of Table 3.
7. Look for any common relationships among the substances in the unknown column and that of the soluble or insoluble substances. The key objective at this point is to remove all of the substances from the unknown column and place them in either the soluble or the insoluble column using logic and the process of elimination. There will be a point where no more substances can be moved from the unknown column by simply looking at laboratory data. At this point, some inferences and generalizations will need to be made. For example, are most (or all) of the nitrate compounds in the same column? How about the ammonium or potassium compounds? Use the categories in Table 4 to help with this step.
8. After completely eliminating the unknown column, examine the substances in the soluble and insoluble columns. Each column should be organized by group (e.g., carbonates, chlorides). Fill in Table 4 with the solubility of each group, including any exceptions that you observe.

Student Worksheet PDF

11826_Student.pdf