Materials Included In Kit

Additional Materials Required

Prelab Preparation

Part 1. Ion Testing

Place 2–3 labeled pipets next to each bottle for dispensing. Labels are provided to help control accidental contamination. To label the pipets, use waterproof ink and write on only one-half of the label. Fold the label in half around the pipet barrel just below the bulb as shown in Figure 1. Labels do not stick well to the pipet but they adhere very well to themselves.

Part 2. Unknowns

The tests in this kit are simplified by testing for one ion at a time. This allows students to clearly see the result from each individual reaction. Therefore, we suggest making the unknowns using a single ion solution. If solutions with more than one ion are desired, it is suggested that a combination of ions that will not interfere with each other are used.

Prepare unknowns by placing approximately 10 mL of unknown ion solution into the provided disposable test tubes. Be sure to label the test tubes and pipets with the provided labels. Assign a number to each unknown. More than one number can be assigned to an ion solution. For example, the chloride ion may be placed in 3 different unknown test tubes (i.e., 1, 7, 12). Unknowns may be presented to the students at the instructor’s discretion. One option is to prepare unknown solutions and place them into test tubes. Then give each lab group tubes of unknowns for testing.

Safety Precautions

See the Safety Precautions section in the student handout. Wear chemical splash goggles, chemical-resistant apron and chemical-resistant gloves. 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 regulations that may apply, before proceeding. Very small amounts of dilute solutions and solid products are generated in this lab. Check with local wastewater authorities to determine if these quantities of barium, lead, silver, chromate and iron can be safely flushed down the drain. If safe, rinse the well plates in the sink with plenty of tap water. If not safe, have students place the compounds from the well plate in a centralized waste container or dispose of the individual compounds according to the following Flinn Suggested Disposal Methods: wells A1, A2, B2, D1 and D2 should the disposed of according to Flinn Suggested Disposal Method #26b. Well B1 should be disposed of according to Flinn Suggested Disposal Method #12a. Well C1 should be disposed of according to Flinn Suggested Disposal Method #27f. Remaining amounts of the reagents included in the kit can be saved for later use or disposed of according to the following Flinn Suggested Disposal Methods. Sodium carbonate, sodium chloride, ferric chloride, potassium phosphate, potassium thiocyantate and sodium sulfate solutions are all disposable by Flinn Scientific Disposal Method #26b. Barium chloride solution should be disposed of following Flinn Scientific Disposal Method #27h. Potassium chromate solution should be disposed of following Flinn Scientific Disposal Method #12a. Hydrochloric acid and nitric acid should be disposed of following Flinn Scientific Disposal Method #24b. Hydrogen peroxide solution should be disposed of following Flinn Scientific Disposal Method #22a. Lead nitrate solution should be disposed of following Flinn Scientific Disposal Method #27f. Silver nitrate solution can be disposed of following Flinn Scientific Disposal Method #11.

Teacher Tips

• This “super kit” and will easily serve 5 sections of 30 students working in pairs, providing enough chemicals for 300 tests for each ion. This lab experiment is designed to be completed in one 50-minute lab period.
• There are 80 labels included in this kit. This will be enough to label the pipets for the 15 solutions and the test tubes and pipets for the unknowns. Labeled pipets can be rinsed out with distilled water, saved and reused with the same solution. Be sure to use waterproof ink or pencil on the labels.
• This activity is designed to be performed in eight stations. Set up the ion tests on eight lab tables and have the student lab groups move from table to table. After students have completed the ion tests in Part 1, have them repeat the stations and perform the tests with the unknowns.
• Caution students to read the labels on the pipets carefully and place the correct pipet back into the corresponding bottle to avoid contamination. Put out only what is needed for that class period in case contamination does occur. To help avoid further contamination, tape or rubberband a small test tube on the side of the bottles and place a pipet in the test tube.
• All of the tests are qualitative. Also, all of the tests depend on the absence of interfering substances in the ion solutions. This may not be the case in actual water samples.
• Prepare enough unknowns to prevent the students from knowing what the unknown solutions are before they even perform the tests.

Sample Data

Record detailed observations inside the circles on the table. Record all color changes that occur. Record whether any gases evolve. If any solid precipitates form, use the abbreviation PPT. If no reaction at all occurs, use the abbreviation NR.

Answers to Questions

Part 1

Answers to Questions 1 and 3 will vary depending on the level of your students. This lab may be performed before your students have the ability to write overall and net ionic equations. Overall and net ionic equations are included for advanced students.

Part 2 

Answers to Questions 2 and 3 will vary depending on the unknown.

References

Heikkinen, H. ChemCom; Kendall/Hunt: Dubuque, Iowa, 1988; pp 29–32.

Mitchell, M. K.; Stapp, W. B. Field Manual for Global Low-Cost Water Quality Monitoring; Kendall/Hunt: Dubuque, Iowa, 1997; pp 29, 35, 36, 47.

Sarkis, V. J. Chem. Ed. 1974, 51, 745–747.

TED Case Studies Minamata Disaster, www.american.edu/projects/mandala/TED/MINAMATA.HTM.

Introduction

What types of pollutants are in our waters? How do these pollutants affect us? In this procedure, the presence of eight different types of polluting ions in water will be tested.

Concepts

• Chemical pollution
• Effects of pollution
• Water quality
• Precipitates

Background

Water is an essential resource for humans. It is used for almost every activity in life and is required for life itself. It is needed for agricultural and industrial use, drinking, transportation, and in recreation. Water often seems to be available in an almost endless supply, but as populations rise and our world becomes increasingly industrialized, more and more water is being utilized. With this extensive use of water, a problem arises: the water becomes polluted and contaminated. This pollution leads to a strain on water’s ability to recycle and cleanse itself of contaminates. It is now estimated that over one billion people are unable to obtainade quate drinking water. The amount of water available, its distribution, and its quality are critical issues that continue to affect all life. An increasing awareness of the need to monitor the quality of water and to locate the sources of pollution is becoming more prevalent in today’s society.

There are two main types of water pollution, point specific pollution and nonpoint pollution. Point specific pollution is contamination that comes from a specific location. An example of point pollution is a factory that has a chemical discharge pipe that leads directly to a water source. This type of pollution can be pinpointed and limited much more readily than the second class of pollutants, nonpoint sources.

Nonpoint water pollution does not come from a specific location. Some examples are runoff of water from city areas, agricultural land, or from poor forestry practices. This type of pollution occurs when runoff water such as snowmelt or rainfall travels over an area of land. As this water moves over the ground, it picks up waste and carries it to a body of water. This water enters rivers and will seep down through the soil and eventually enter the groundwater supply.

As polluted water enters the groundwater supply or any other water source, the concentrations of certain ions may alter the water’s purity. If the concentration of an ion reaches a certain level, the water could become hazardous. Here are some of the sources and potentially dangerous effects of the ions that will be studied in this activity:

Carbonate Ion: Comes from the high water solubility of carbonate material and rocks such as limestone and dolomite. Another source of carbonate ion is from dissolved atmospheric carbon dioxide. When heated in the presence of calcium and magnesium, alkaline water containing carbonates will form crust-like scales in pipes restricting the flow of fluids and also causing the release of carbon dioxide gas.

Chloride Ion: Dissolved from rocks and soils and present in sewage and industrial wastes. When chloride is in excess of 100 parts per million, water has a salty taste and when it is in excess of 150 parts per million, physiological damage may occur. Chloride also increases the corrosiveness of water when it is present in higher concentrations.

Chromate Ion: Comes from industrial waste and is used to prevent corrosion in cooling towers. When chromate accumulates in large amounts in the human body it may cause cancer.

Iron Ion: Present in natural sources such as rocks and soils. Iron is also found in industrial waste and is present from the corrosion of iron pipes. When the concentration of iron is above 100 parts per billion, it will precipitate when it comes in contact with air. This will in turn stain laundry, plumbing fixtures, and silverware. It will also cause food and drinks to taste and look peculiar.

Lead Ion: Found in water from plumbing, coal and gasoline sources. A major source of lead pollution came from lead additives in gasoline prior to the 1980s (the structure of the gas has since been changed to cut down on the pollution risk). The EPA estimates that 20% of our exposure to lead comes from drinking water. At blood levels greater than 100 parts per billion, anemia, kidney damage, and mental retardation can result.

Phosphate Ion: Comes from fertilizers, detergents, wastewater of domestic origin (e.g., human, animal and plant residue) and from wastewaters of industrial origin. Phosphate is added to farm and city water systems to control hardness. Phosphates from laundry detergents can result in overgrowth of algae, which in turn will cause the algae to die at a high rate and undergo decomposition. This decomposition process depletes oxygen from the water and will result in increased fish kill.

Sulfate Ion: Dissolved from rocks and soils that contain sulfides and gypsum. Sulfate is also due to industrial waste in liquid or gaseous forms. When sulfate is present with calcium, scale will result in pipes and steam boilers. Sulfate concentrations of 500 parts per million produce water that tastes bitter and sulfate concentrations of 1,000 parts per million may be cathartic.

Materials

Safety Precautions

Barium chloride solution is toxic by ingestion. Ferric chloride solution may be a skin and tissue irritant. Hydrochloric acid solution is toxic by ingestion or inhalation and is corrosive to the skin and eyes. Hydrogen peroxide solution is an oxidizer and a skin and eye irritant. Lead nitrate solution is moderately toxic by ingestion and inhalation; a strong oxidant and a dangerous fire risk in contact with organic material; a body tissue irritant and is a possible carcinogen. Nitric acid solution is corrosive, moderately toxic by ingestion and inhalation and is a strong oxidizing solution; avoid contact with acetic acid and readily oxidized substances. Potassium chromate solution is moderately toxic by ingestion and may be corrosive to body tissue. Potassium thiocyanate solution is moderately toxic by ingestion and may emit toxic cyanide gas if heated to decomposition or in contact with concentrated acids. Silver nitrate solution is a corrosive solid, causes burns and is highly toxic; avoid contact with eyes and skin. Sodium carbonate solution may be a skin irritant. Wear chemical splash goggles, chemical-resistant apron and chemical-resistant gloves. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part 1. Testing for the Presence of Ions in Known Solutions

Carbonate Ion, CO₃^2–

1. Place 10 drops of carbonate ion solution into well A1 of the reaction plate.
2. Add 7 drops of 1.0 M hydrochloric acid solution. Record all observations in the data table.

Chloride Ion, Cl^–

3. Place 5 drops of chloride ion solution into well A2 of the reaction plate.
4. Add 5 drops of 0.1 M silver nitrate solution to this well. Be sure to avoid contact with skin, as silver nitrate will stain skin and clothing. Record all observations in the data table.

Chromate Ion, CrO₄^2–

5. Place 4 drops of 3.0 M nitric acid solution into well B1 of the reaction plate.
6. Add 4 drops of the chromate ion solution to the well.
7. Add 7 drops of distilled water. Stir the solution with the water pipet.
8. Quickly add 4 drops of 3% hydrogen peroxide. Record all observations in the data table.

Iron(III) Ion, Fe³⁺

9. Put 5 drops of the iron(III) ion solution into well B2 of the reaction plate.
10. Add 3 drops of 0.5 M potassium thiocyanate solution. Record all observations in the data table.

Lead Ion, Pb²⁺

11. Place 3 drops of the lead ion solution into well C1 of the reaction plate.
12. Add 2 drops of the chromate ion solution (also used in the chromate ion test). Record all observations in the data table.

Phosphate Ion, PO₄^3–

13. Put 5 drops of the phosphate ion solution into well D1 of the reaction plate.
14. Add 3 drops of 0.1 M silver nitrate solution to the well. Record all observations in the data table.

Sulfate Ion, SO₄^2–

15. Place 5 drops of sulfate ion solution into well D2 of the reaction plate.
16. Add 3 drops of 0.1 M barium chloride solution. Record all observations in the data table.

Part 2. Testing for the Presence of Ions in Unknown Solutions

17. Obtain an unknown solution from your instructor. Be sure to record the unknown number in the data table.
18. Repeat the testing procedure steps outlined in Part 1 using wells A3, A4, B3, B4, C3, D3 and D4. In each case, use your unknown solution in place of the ion solution. For example, when testing for the presence of carbonate ion, you will add 10 drops of your unknown solution plus 7 drops of 1.0 M hydrochloric acid solution to well A3. The chromate ion test solution will be used to test for the presence of lead ions.
19. Record all observations in the data table.
20. Repeat steps 19–21 for a second unknown solution using wells A5, A6, B5, B6, C5, D5 and D6.
21. See instructor for appropriate disposal procedures. After the final products have been disposed of, rinse each well thoroughly with distilled water and dry with a cotton swab.

Student Worksheet PDF

11883_Student1.pdf