Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Shake the placer sand to evenly mix the sand with the copper shot.
2. Pour equal amounts of the sample into 10 different containers.
3. Fill the containers half-full with water.

Safety Precautions

Although the materials in this lab are nonhazardous, please use normal laboratory safety precautions. Use caution to avoid spilling the samples on the floor as it may cause someone to slip and fall. 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. All materials included in this kit may be saved for future use.

Lab Hints

• Enough materials are provided in this kit for 32 students working in groups of four. This laboratory activity may be completed in one 50-minute class period.
• Streak plates may be washed off using a mild detergent and shared by groups of students.
• Pyrite nuggets may be washed off using a mild detergent to make them shinier.
• The placer sand contains copper shot, which may be removed from the cellophane tape that students exchange for their iron pyrite nugget, and returned to the sand. Note: This copper shot is not actually melted down, it is only exchanged for an iron pyrite nugget.
• Setting a time limit or determining the number of “gold” flakes each group should present to be “melted down” into a nugget will ensure that the students have adequate exposure to the process.
• An optional claim registration is provided and may be copied to distribute to each group or used for the entire class.

Teacher Tips

• The panning part of this activity provides a practical and historical application for the importance of density in society.
• Use the California gold rush of 1849 as a historical perspective to tie this activity into the history curriculum.
• To show the students the effects of mining on the environment, take a chocolate chip cookie and have them, using a toothpick and plastic spoon, remove a specified number of chips from the cookie. Once they have removed the chip ask the students to put the cookie back together.

Sample Data

Answers to Questions

1. Although the value of gold fluctuates every day, assuming that the nugget is real gold, what would it be worth if the current price of gold was $13.50/g?

   $603.45

2. Based on the density and results of the streak test, is the nugget real gold? Explain.

   No, the streak was greenish-brown and the density was well below 19.3 g/cm³.

3. Does fool’s gold (pyrite) have any commercial significance? Explain.

   Yes, it is a source of sulfur for the manufacture of sulfuric acid.

Teacher Handouts

13077_Teacher1.pdf

Introduction

Gold has been discovered in Copper River! Put your panning skills to the test and see if you can strike it rich. Be careful—many former prospectors are now penniless from failed ventures!

Concepts

• Density
• Mineral assay

Background

The Copper River, which gets its name from the shiny copper color it turns at dusk when the Sun’s rays reflect off of it, is a majestic river that meanders past Peachtree Plateau. Gold has recently been discovered in a section of the river around Peachtree Plateau and now the area has become home to many adventurous gold prospectors. The prospectors left their homes and families to try and strike it rich and start anew with their newfound wealth. Hopefully, they will return home with large sums of money, unlike many of the prospectors during the California Gold Rush in the 1840s and 1850s. Unfortunately, large deposits of iron pyrite have also been discovered in Copper River.

The type mining used when panning for gold is called placer mining. Placer is a Spanish word meaning “pleasure,” because it was easier to use a gold pan than a shovel or a pick. This open-pit type of mining is done by excavating at the surface and does not require tunneling. In placer mining, gold is extracted from alluvial deposits, which are sediments deposited by flowing water, by the differential settling of materials.

Iron pyrite (iron sulfide—FeS₂), also called fool’s gold, is a gold-colored mineral that is commonly mistaken for real gold. According to the United States Geological Survey, other minerals, such as chalcopyrite and biotite mica, can also mimic gold’s distinctive color.

Gold and pyrite can be distinguished based on their appearance and other physical properties. Although gold and pyrite both have a brilliant metallic luster, gold is more silvery yellow, and pyrite looks much more like brass. While pure gold maintains its luster, pyrite sometimes tarnishes with a bronze or iridescent iron oxide. Pyrite usually forms crystals, although it can form shapeless grains. Gold is found in grains, as well as nuggets and flakes. Gold is very soft and can be scratched, where pyrite is hard and cannot be easily scratched. Pyrite is also less dense and more brittle than gold. Gold is a very dense substance, with a density of 19.3 g/cm³; whereas pyrite has a lower density of 5 to 8 g/cm³, depending on the relative percentages of iron and sulfur. When pyrite is rubbed with a hard object it gives off a sulfur smell, but gold will not. When struck with a steel hammer, gold will flatten out into a sheet because it is malleable. Pyrite will actually give off sparks when struck with a steel hammer. When rubbed on an unglazed porcelain tile, pyrite streaks from greenish-brown to black and gold streaks golden yellow.

Pyrite is a commercially significant source of sulfur for the manufacture of sulfuric acid. In fact, it is the most important source of sulfur next to native sulfur. The most notable occurrences of pyrite in the U.S. are in Illinois and Missouri.

Gold, unlike the compound pyrite, is an element (Au) and a precious metal. In fact, gold is the oldest precious metal known to man. Gold is the most malleable and ductile (it can be drawn into thin wires) of all metals. Its magnificent luster allows for the most exquisite and coveted jewelry. Because of its scarcity, workability, luster, resistance to tarnish and intrinsic appeal to humans, gold has always been treasured.

Experiment Overview

Identify the densest material in Copper River and determine, by density and streak plate results, if you have found gold or if you have been “fooled.”

Materials

Safety Precautions

Although the materials in this lab are nonhazardous, please follow normal laboratory safety precautions. Use caution to avoid spilling the samples on the floor as this may cause someone to slip and fall. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Panning

1. Place about three handfuls of placer sand material into the gold pan.
2. Submerge the pan into its stream (dish tub).
3. While holding the gold pan under water, move the pan in a circular motion so that the lighter materials will be carried out of the gold pan. Note: Don’t move it too rapidly or the gold may be lost along with the rocks and sand.
4. Continue swirling until about half of the material in the gold pan is gone.
5. Lift the pan out of the water.
6. Begin swirling it around with the gold pan tipped slightly to the side with the riffles (see Figure 1).
   {13077_Procedure_Figure_1}
7. When all the water is gone, dip the pan into the water again.
8. Bring the pan back out of the water and start swirling again.
9. Repeat steps 7 and 8 until nearly all the material in the pan is gone.
10. Use a pipet or wash bottle to spray water into the pan and separate any nuggets or flakes of “gold” from the sand in the bottom of the gold pan.
11. Using forceps, remove the “gold” from the pan and place the “gold” on a piece of cellophane tape.
12. Take the “gold” to your instructor to be melted down into a nugget that will be assayed.

Assay

13. Note the appearance of the nugget and record observations in the data table.
14. Using a 250-mL graduated cylinder, determine the volume of the gold nugget using water displacement.
15. Record the volume of the nugget in the data table.
16. Using a balance, measure the mass of the gold nugget.
17. Record the mass in the data table.
18. Determine the density of the nugget using the formula density = mass/volume, where the mass is in grams and the volume is in cubic centimeters (1 cm³ = 1 mL). Record the density in the data table.
19. Using a streak plate, rub the nugget across the plate and observe the streak color.
20. Record the streak color in the data table.
21. Determine the identity of the nugget by its density and the results of the streak test.
22. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13077_Student1.pdf