Materials Included In Kit

Additional Materials Required

Prelab Preparation

Unknown Sulfate Ion Sample: Reduce the 0.1 M sodium sulfate solution concentration to a concentration of 0.005 M by pipetting 5 mL of the 0.1 M solution into a 1-L volumetric flask. Fill the flask to the mark with distilled or deionized water. Mix well.

Unknown Chloride Ion Sample: Reduce the 0.1 M sodium chloride solution concentration to a concentration of 0.010 M by pipetting 10 mL of the 0.1 M solution into a 1-L volumetric flask. Fill the flask to the mark with distilled or deionized water. Mix well.

Safety Precautions

Silver nitrate solution is toxic and irritating to body tissue; avoid contact with eyes and skin. Silver nitrate also will stain skin and clothes. Barium nitrate solution is toxic by ingestion. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. 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. Leftover silver nitrate solution may disposed of by precipitating as silver chloride according to Flinn Suggested Disposal Method #11. Unused barium nitrate solution may be disposed of by precipitating as barium sulfate according to Flinn Suggested Disposal Method #27h.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• Two of the most basic and important techniques to master in chemical analysis are filtering and decanting. These two techniques of quantitative transfer occur as crucial steps in many analytical determinations. To make sure the filtering speed is as rapid as possible, the filter paper must be seated properly in the funnel. The filter paper should make complete contact with the sides of the funnel and drain with few, if any, air bubbles in the stem. This is done by folding the filter paper as shown in Figure 4 and tearing off the corner. This allows the subsequent cone of filter paper to be placed smoothly against the sides of the funnel. Place the filter paper cone in the funnel. Wet the filter paper thoroughly with distilled or deionized water and use your fingers to smooth the paper against the sides of the funnel until no air bubbles are visible in the stem.
  {13505_Hints_Figure_4}
• Proper decanting technique ensures that the precipitate is transferred from the beaker to the filter paper and little, if any, is lost during the transfer. Start by holding a stir rod against the lip of the beaker and pour the liquid from the beaker into the funnel. The liquid should run down the rod and into the funnel without splashing (see Figure 5).
  {13505_Hints_Figure_5}
  Keep the level of the liquid in the funnel below the top of the filter paper. When all the liquid has been transferred to the funnel, begin transferring the remaining precipitate from the beaker to the funnel. Add a stream of distilled or deionized water to the beaker. Use a rubber policeman on the end of the stir rod to loosen any precipitate clinging to the beaker. Rinse the rubber policeman with a stream of distilled or deionized water, swirl the beaker to suspend the precipitate, and transfer the suspension to the funnel using the technique outlined in Figure 5. Repeat this rinsing until nearly all the precipitate has been transferred. Rinse the beaker again and transfer the liquid to the flask. Hold the beaker and stir rod as shown in Figure 6 and rinse the sides and bottom of the flask with distilled or deionized water. Rinse at a rate that allows the liquid to flow down the stir rod into the funnel without splashing and doesn’t allow the liquid level to rise above the top of the filter paper. Repeat this rinse until no precipitate is visible in the beaker.
  {13505_Hints_Figure_6}
  Teachers should demonstrate these techniques to the students and allow those not yet proficient sufficient time to practice setting up the filter paper in the filter cone and decanting a liquid from a flask.
• If no drying oven is available, an evaporating dish or large porcelain crucible and Bunsen burner can be used. Place the solid and paper in the evaporating dish or crucible and heat gently over a Bunsen burner for a few minutes. Make sure the paper is not exposed to the flame and do not allow the paper to char. In this manner, the moisture can be driven off without destroying either the filter paper or the precipitated calcium carbonate.
• You can vary the amount of sample the student uses to increase or decrease the amount of precipitate formed.

Teacher Tips

• There are many examples worldwide of heavy metal pollution gone undetected with tragic consequences. Mercury contamination in the fishing village of Minamata, Japan; heavy metal contamination from abandoned mines in Colorado; and heavy metals and radioactive releases from a weapons plant in Hanford, Washington, to name a few.

Answers to Prelab Questions

Read the Background section and procedure thoroughly, and then answer the following questions.

A sample was submitted to determine the identity of copper pollutant and its concentration. The initial testing gave a positive test for the presence of sulfate ion, with little to no positive test for chloride ion.

The sample volume was reduced from 500 mL to 50 mL. A quantitative test for sulfate ion was performed on this 50-mL sample and yielded the following data:
Mass of filter paper + BaSO₄ ___1.102 g___
Mass of filter paper ___1.001 g___
Mass of BaSO₄ ___0.101 g___

1. Determine the moles of sulfate ions in the 50-mL sample.

   Moles SO₄^2– = moles BaSO₄ = (mass of BaSO₄)/233.43 g/mol BaSO₄ = 0.101 g/233.43(g/mol) = 4.33 x 10^–4 moles

2. Assuming all the sulfate came from copper sulfate contamination; determine the mass, in milligrams, of copper ions in the 50-mL sample.

   Moles of sulfate = moles of copper = 4.33 x 10^–4 moles
   Grams of copper = moles of copper x 63.54 g copper/mole

   = (4.33 x 10^–4 moles) x 63.54 g copper/mole
   = 0.0275 grams copper

3. Parts per million (ppm) is a standard unit of concentration used to identify levels of pollutants in lakes, streams and ground waters. The units are microgram, μg, per gram, or milligram, mg, per liter.

   Calculate the ppm (mg/L) of copper in the original 500 mL sample. If the EPA standard for copper concentration sanctions is 5.0 ppm, are legal proceedings in order for this pollution violation?
   ppm copper = {0.0275 g copper x (1000 mg/1.0 g)}/{500 mL x (1.0 L/1000 mL)}
   ppm copper = 27.5 mg/0.5 L = 55.0 ppm
   Yes, criminal proceedings are in order.

Sample Data

Chloride Ion Unknown Solution

Part 1

Part 2 Sulfate Ion Unknown Solution

Part 1 Part 2

Answers to Questions

Chloride Ion Unknown Solution

1. Which company was responsible for the copper discharge?

   Acme Electronics

2. Based on the Part 2 data, calculate the equivalent mass of copper in the sample.

   Moles Cu²⁺ = ½ mole Cl^– = ½ mole AgCl

   =0.5 (0.078 g)/(169.87 g/mol)
   =2.30 x 10^–4 moles

   Mass Cu = (2.30 x 10^–4 moles) x 63.55 g Cu/mol
   Mass Cu = 0.015 g Cu

3. The sample volume was reduced from 500 mL to 50 mL. Parts per million (ppm) is a standard unit of concentration used to identify levels of pollutants in lakes, streams, and ground waters. The units are microgram (μg) per gram, or milligram (mg) per liter.

   Calculate the ppm (mg/L) of copper in the original 500 mL sample. If the EPA standard for copper concentration sanctions is 5.0 ppm, are legal proceedings in order for this pollution violation?
   mg Cu = 0.015 g Cu x 1000 mg/g = 15 mg Cu
   ppm Cu = 15 mg/0.5 L = 30 ppm Cu
   Legal proceedings are in order.

Sulfate Ion Unknown Solution

1. Which company was responsible for the copper discharge?

   Ironic Steel

2. Based on the Part 2 data, calculate the equivalent mass of copper in the sample.

   Moles Cu²⁺ = moles SO₄^2– = moles BaSO₄

   = (0.055 g)/(233.43 g/mol)
   = 2.36 x 10^–4 moles

   Mass Cu = (2.36 x 10^–4 moles) x 63.55 g Cu/mol
   Mass Cu = 0.015 g Cu

3. The sample volume was reduced from 500 mL to 50 mL. Parts per million (ppm) is a standard unit of concentration used to identify levels of pollutants in lakes, streams, and ground waters. The units are microgram (μg) per gram, or milligram (mg) per liter.

   Calculate the ppm (mg/L) of copper in the original 500-mL sample. If the EPA standard for copper concentration sanctions is 5.0 ppm, are legal proceedings in order for this pollution violation?
   mg Cu = 0.015 g Cu x 1000 mg/g = 15 mg Cu
   ppm Cu = 15 mg/0.5 L = 30 ppm Cu
   Legal proceedings are in order.

References

Special thanks to Gary Schiltz, retired, Glenbard West High School, Glen Ellyn, IL, for providing the idea and the instructions for this activity to Flinn Scientific.

Introduction

Water pollution is a crime often difficult to solve. While identifying the specific pollutant may be straightforward, locating its source may take serious investigation.

Concepts

• Gravimetric analysis
• Mole ratio
• Solubility
• Qualitative analysis

Background

In August of 2011, a spike of copper concentration was detected in the Lazy River downstream from the industrial park south of Bedford Falls. Two possible sites in the industrial park may be responsible for the spill. The first, Acme Electronics, occupies the building at 148 Bonnie Meadow Road. Acme generates copper chloride waste from its circuit board etching operations. The second, Ironic Steel, is located at 742 Evergreen Terrace. Ironic uses copper sulfate as an electrolyte in their coated steel wire production.

You are to gather data to determine which company is responsible for the spill. The decision as to whether criminal proceedings are warranted will be based on your findings.

If the spill stems from faulty operations at Acme, then elevated levels of chloride ions should accompany those high values for copper ions. If, however, Ironic is at fault, then you will see a spike in the concentration of sulfate ions.

You will be given a representative sample of the Lazy River. This 50-mL sample has been concentrated from an initial sample of 500 mL.

Part 1 consists of qualitative test to determine which ion, chloride, Cl^–, or sulfate, SO₄^2–, is present in the river sample. This will identify the industrial site responsible for the spill.

If chloride ion is present, the addition of a silver nitrate solution will result in a precipitation of silver chloride.

If only sulfate ions are present in quantity, no precipitation will occur, since AgSO₄ is a soluble compound.

If sulfate ions are indeed present, the addition of a barium nitrate solution will result in a precipitation of barium sulfate. If only chloride ions are present in quantity, no precipitation will occur, since BaCl₂ is a soluble compound.

In Part 2 you will determine the level of contamination in the Lazy River. By adding the appropriate solution, you will precipitate out the identified anion from the Lazy River sample.

If chloride ions are present, add silver nitrate solution. If sulfate ions are present, add barium nitrate solution. You will filter out, dry, and then mass your solid precipitate. You then use this mass value to calculate the moles of anion present in the sample and use the appropriate mole ratio to determine the moles of copper in the sample.

Convert this mole value to mass of copper.

Experiment Overview

The purpose of this lab is to identify the anion associated with the copper ion discharge and thus the source of the discharge. Once identified, you will employ quantitative analysis to determine the level of copper pollution.

Materials

Prelab Questions

Read the Background section and procedure thoroughly, and then answer the following questions.

A sample was submitted to determine the identity of copper pollutant and its concentration. The initial testing gave a positive test for the presence of sulfate ion, with little to no positive test for chloride ion.

The sample volume was reduced from 500 mL to 50 mL. A quantitative test for sulfate ion was performed on this 50 mL sample and yielded the following data:

The sample volume was reduced from 500 mL to 50 mL. A quantitative test for sulfate ion was performed on this 50 mL sample and yielded the following data:

Mass of filter paper + BaSO₄ ___1.102 g___
Mass of filter paper ___1.001 g___
Mass of BaSO₄ ___0.101 g___

1. Determine the moles of sulfate ions in the 50-mL sample.
2. Assuming all the sulfate came from copper sulfate contamination; determine the mass, in milligrams, of copper ions in the 50-mL sample.
3. Parts per million (ppm) is a standard unit of concentration used to identify levels of pollutants in lakes, streams, and ground waters. The units are microgram, μg, per gram, or milligram, mg, per liter.

   Calculate the ppm (mg/L) of copper in the original 500-mL sample. If the EPA standard for copper concentration sanctions is 5.0 ppm, are legal proceedings in order for this pollution violation?

Safety Precautions

Barium nitrate solution is toxic by ingestion. Silver nitrate stains skin and clothing; however, the stains may not appear for several hours. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

Part 1. Identifying the Anion

1. Place 2.5 mL of the unknown copper solution in each of two test tubes.
2. Add 10 drops of 0.2 M silver nitrate, AgNO₃, to the first test tube. If chloride ion is present a precipitate of AgCl will form.
3. Add 10 drops of 0.2 M barium nitrate, Ba(NO₃)₂, to the second test tube. If sulfate ion is present a precipitate of BaSO₄ will form.
4. Record your results in the Part 1 data table.

Part 2. Quantifying the Copper Compound

1. Add 50 mL of the unknown copper solution to a clean 250-mL beaker.
2. Add about 5 mL of either the 0.2 M AgNO₃ solution or the 0.2 M Ba(NO₃)₂, to the 250-mL beaker, depending on which caused the formation of a precipitate in Part 1. Stir.
3. Let the precipitate settle (5 minutes).
4. Obtain a piece of quantitative filter paper. Weigh the filter paper on the analytical balance.
5. Record the mass of the filter paper in the data table.
6. Fold the filter paper into a cone. First fold the filter paper in half and crease. Next, fold the filter paper almost in half again, leaving about a 5° angle between the folded edges (see Figure 1).
   {13505_Procedure_Figure_1}
7. Tear off the corner of the top edge, open the filter paper into a cone shape, and place the torn corner in the bottom of the cone. Place the cone into the filter funnel. Position the paper tight against the funnel walls and moisten the paper with about 5 mL of deionized water from a wash bottle. Note: After adding the water, use index fingers to seat the filter paper tightly against the sides of the funnel so that little, if any, air gaps are visible in the stem as the water filters through.
8. Set up the ring stand and iron ring and place the funnel in the ring.
9. Let the funnel drain into a second 250-mL beaker (see Figure 2).
   {13505_Procedure_Figure_2}
10. Using a stirring rod, decant the liquid from the 250-mL beaker into the funnel. Be sure to keep the liquid level below the top of the filter paper cone (see Figure 3).
    {13505_Procedure_Figure_3}
11. When all but approximately 10 mL of the liquid has been transferred, swirl the beaker to suspend the precipitated BaSO₄ or AgCl.
12. Transfer this to the funnel, again making sure not to fill the cone above the top of the filter paper.
13. Rinse the flask with small amounts of distilled or deionized water from the wash bottle and then transfer the washings to the filter.
14. When all the solid has been transferred to the filter paper, rinse the solid with three small por¬tions of distilled or deionized water. Allow the funnel to drain completely.
15. Obtain a watch glass. Using a microspatula, take the filter paper out of the funnel and place it in the center of the watch glass. Be careful not to tear the paper or to lose any part of the solid.
16. Using the microspatula, carefully open the filter paper into a circle on the watch glass. Place the watch glass and filter paper in a drying oven set at 110–120 °C.
17. Allow the filter paper to dry for 10–15 minutes. Remove the watch glass from the oven using crucible tongs. Use the spatula to break up the BaSO₄ or AgCl into small particles.
18. Return the watch glass to the drying oven for an additional 5 minutes.
19. Remove the watch glass from the oven and set it aside to cool.
20. When cool, weigh the filter paper and the solid precipitate on an analytical balance. Record the mass in the data table.
21. Repeat steps 17–19 until the mass readings do not change by more than 0.005 g.
22. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13505_Student1.pdf