Creating Elements

Introduction

Over time, students become familiar with the properties of elements and their characteristic reactions to form compounds and molecules. In this three-part demonstration, show the other side of that coin by using characteristic reactions to produce elements from compounds.

The set of three demonstrations includes:

1. Tin, Sn—What happens in an electrolytic cell if one of the ions in the electrolyte may be both oxidized and reduced? Electrolysis of tin(II) chloride provides a stunning example. Grow a beautiful “tin-man” crystal tree by running an electric current through a solution of tin(II) chloride. Students will enjoy this “electric” oxidation–reduction demonstration as elemental tin is produced. What happens if the current is reversed?
2. Silver, Ag—A copper wire coil is suspended in a silver nitrate solution. The coil is soon coated with shiny elemental silver “needles” and the solution turns blue as silver ions are replaced by copper ions.
3. Carbon, C—Your students will be amazed as they watch a yellow solid–liquid mixture turn brown, then black, expand out of the top of the beaker, and solidify. The beaker becomes extremely hot and the odor of burnt sugar. The solid black product is pure elemental carbon!

The demonstrations in this kit may be presented in a variety of ways. The demonstrations may be done randomly for student enjoyment or they may be used to review properties of elements (metals and nonmetals) and classifying reactions (redox, single replacement, decomposition). They may be done in order of element type as a review. Student data sheets and questions are included as an optional assessment tool for the instructor. The kit contains enough materials to perform all the demonstrations three times.

Concepts

• Electrolysis
• Cathode
• Anode
• Oxidation–reduction
• Single replacement reaction
• Dehydration reaction
• Exothermic reactions

Materials Included In Kit

Additional Materials Required

Experiment Overview

Creating Silver Metal

The reaction of copper wire with aqueous silver nitrate shows chemistry in action—delicate silver crystals grow on the wire surface and the color of copper(II) ions gradually appears in solution in this example of a single replacement, oxidation–reduction reaction.

Materials

Safety Precautions

Acidic tin(II) chloride solution is a 1 M hydrochloric acid solution that is corrosive to body tissue and moderately toxic by ingestion. Silver nitrate solution is mildly toxic by ingestion and it will stain skin and clothes. Sulfuric acid is severely corrosive to eyes, skin and other tissue. It generates considerable heat of dilution with water; mixing with water may cause spraying and spattering. Avoid contact of all chemicals with eyes and skin. Perform the Creating the Element Carbon demonstration only in an efficient fume hood or a well-ventilated room. Do not handle the carbon product with your hands; use tongs. The carbon product will contain unreacted, corrosive sulfuric acid. Neutralize acid spills and the carbon product with sodium carbonate. The steam produced by the reaction can cause burns. Do not stand over the reaction vessel or inhale the steam produced. The reaction vessel will get extremely hot; allow the vessel to cool before handling. Use only borosilicate glass beakers for the Creating the Element Carbon demonstration. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please consult 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 tin(II) chloride solution may be neutralized according to Flinn Suggested Disposal Method #24b. All solid waste may be disposed of in the trash according to Flinn Suggested Disposal Method #26a. The copper wire and the plated silver may be carefully removed from the solution and disposed of according to Flinn Suggested Disposal Method #26a. The solution may be disposed of according to Flinn Suggested Disposal Method #26b. When the reaction is complete and the reaction vessel is cool, sprinkle the carbon product with sodium carbonate to help neutralize any remaining acid. Remove the carbon product from the reaction vessel using tongs and thoroughly rinse the carbon product under running water. Place the carbon lump inside a plastic bag and dispose according to Flinn Suggested Disposal Method #26a.

Procedure

Creating the Element Tin

1. Place a clean Petri dish on an overhead projector or document camera.
2. Fill the dish approximately ½ full (15–22 mL) with 1 M tin(II) chloride solution.
3. Attach paper clips to opposite sides of the Petri dish.
4. Attach the alligator clips from the 9-V battery cap to each paper clip.
5. Hook the battery cap to the 9-V battery and observe the changes at the anode and the cathode. A faint milky white suspension of tin(IV) chloride appears at the anode and metallic tin(0) crystals form at the cathode (see Figure 1).
6. Allow the current to run for approximately one minute to see the continued growth. The tin(0) crystals form feather-like projections and grow across the dish.
7. Remove the alligator clip leads from the paper clips and switch the polarity of the electrodes by changing which paper clip the leads are attached to. The previous cathode will now be the anode and vice versa.
8. The crystal formation will reverse—tin crystals will grow at the “new” cathode and the existing crystals at the “new” anode will dissolve back into solution.

Creating Silver Metal

1. Cut a 30-cm piece of copper wire and loosely coil it into the shape shown in Figure 2.

2. Add distilled water to the 110-mL mark of a clean, 250-mL beaker.
3. Fill the beaker to the 145-mL mark (add 35 mL) with 0.1 M AgNO₃. Stir the solution with a clean stirring rod.
4. Use a wood splint to suspend the copper wire in the silver nitrate solution, as shown in Figure 2. The copper wire should not be touching the bottom or sides of the beaker.
5. Shiny needles will be apparent on the surface of the wire within several minutes. Allow the reaction to proceed for approximately 15 minutes to see the blue color of copper ions develop and the reaction to proceed to completion.

Creating the Element Carbon

1. All safety precautions must be followed. Perform this experiment only in a fume hood or in a well-ventilated room.
2. Add 50 g of sucrose to a 250-mL borosilicate beaker.
3. Place the beaker on a layer of paper towels.
4. Using a 100-mL graduated cylinder, carefully measure 50 mL of concentrated sulfuric acid. (Wear gloves and neutralize any acid spills with sodium carbonate.)
5. Slowly and carefully pour the sulfuric acid into the beaker containing sucrose.
6. Stir briefly with a glass stirring rod. Leave the stirring rod inside the beaker. It will help support the column of carbon produced.
7. Stand back and observe. In a few minutes the solution starts to bubble and expand. Steam will be visible coming out of the mouth of the beaker. The beaker will get hot. The carbon “soufflé” reaction takes 15 minutes from addition of the sulfuric acid to the hardening of the carbon product.
8. Allow the beaker to cool; then follow the cleanup and disposal procedure.

Student Worksheet PDF

11767_Student1.pdf

Teacher Tips

• In Creating the Element Tin, the paper clips may turn black in the tin(II) chloride solution due to a reaction between the metal paper clip and the tin(II) ions. This does not affect the demonstration.
• Place a small piece of copper wire in the center of the Petri dish so that the ends are pointing at both of the alligator clips. When the electric current starts, tin metal will precipitate at the anode and crystals will grow at the cathode. The copper wire functions as a second electrode, therefore repeating the pattern.
• Place the Petri dish on top of a sheet of clear acetate transparency and place (+) and (–) signs on the sheet to show the polarity of the electrodes.
• For Creating Silver Metal, the copper wire may be surface cleaned with a paper towel and reused for each demonstration.
• The crystals of silver that form will range from white to gray in appearance.
• Three to four drops of 3 M nitric acid may be added to the reaction mixture to initiate the reaction and speed up the demonstration.
• In Creating the Element Carbon, use the transition period between the addition of the sulfuric acid and the onset of visual observations to discuss the chemical reaction.

Answers to Questions

Creating the Element Tin

The original conducting solution contains tin(II) chloride (SnCl₂). The products of the electrolysis reaction are tin(0) and tin(IV) chloride.

1. Draw two sketches representing your observations during the first and second parts of this demonstration. Indicate the sign of each electrode.

First Demonstration

Second Demonstration

Accept any reasonable student sketches.

2. How did the two products differ in appearance?

One of the products [tin(0)] has a metallic, crystalline appearance, growing in feather-like projections outward from the negative electrode (cathode) and expanding across the Petri dish. The other product [tin(IV) chloride] is a milky white suspension that remained localized near the electrode (anode).

3. Identify the product that was obtained at the anode and at the cathode, respectively.

Anode – tin(IV) chloride Cathode – tin(0), tin metal

4. The electric current causes an oxidation–reduction reaction within the conducting solution.

a. Which product results from reduction of tin(II) ions?

Tin(0)

b. Which product results from oxidation of tin(IV) ions?

Tin(IV) chloride

5. What was observed when the “sign” or polarity of the electrodes was switched?

The products seemed to “reverse” their position. The original tin crystals and tin(IV) precipitate slowly redissolved and disappeared. Once the products from the first demonstration completely dissolved back into solution, new products formed at both electrodes. Since the placement of the anode and cathode was switched, the location of each product was also reversed.

Creating Silver Metal

1. Describe what happened in this demonstration.

A copper wire coil is suspended in a colorless solution. The coil develops white to gray “needles” and the solution becomes blue.

2. Write a balanced chemical equation showing the oxidation–reduction reaction of copper metal and silver ions.

Creating the Element Carbon

1. Describe what happened in this demonstration.

Concentrated sulfuric acid was added to a large amount of sucrose. The mixture was stirred. After several minutes, it began to bubble and “dry up.” The mixture began to expand upward, and steam was visible at the top of the beaker. After about 15 minutes the substance appeared to be completely dry, and there was a black column of carbon rising up out of the beaker.

2. Write a balanced chemical equation showing the dehydration of sucrose (C₁₂H₂₂O₁₁).

C₁₂H₂₂O₁₁(s) → 12C(s) + 11H₂O

3. Sucrose is a form of stored energy used by plants. How does this demonstration show what happens to that energy when the “food” is consumed?

The dehydration represented the consumption of the sugar. As it occurred, energy was released in the form of heat. So much energy was released that the beaker grew hot and the carbon was forced to expand and rise out of the beaker. This shows not only the great amount of energy stored in sugar but the fact that energy is released when the food storing it is consumed.

Discussion

Creating the Element Tin

This demonstration utilizes an electric current to cause an oxidization–reduction reaction within a solution of tin(II) chloride. Tin(II) ions are oxidized to an insoluble precipitate of tin(IV) chloride ions at the anode and reduced to metallic tin [tin(0)] at the cathode.

The overall reaction is called a disproportionation reaction—a chemical reaction in which one reagent acts as both oxidizing and reducing agent. As a result, the reagent (Sn²⁺ ions) is converted into both a more oxidized and a more reduced product. The process of using an electric current to cause a redox reaction is called electrolysis.

Creating Silver Metal

The silver ions in solution are reduced by the copper metal in an oxidation–reduction reaction.

The copper(II) ions formed during the reaction will impart a blue color to the solution. The overall reation is an example of a single-replacement reaction.

Creating the Element Carbon

Plants combine carbon dioxide and water in the presence of chlorophyll and sunlight to produce food and oxygen. The food is stored energy for the plant and is in the form of sugars or carbohydrates. Sugars have a molecular formula of nC•H₂O (e.g., sucrose C₁₂H₂₂O₁₁, glucose C₆H₁₂O₆ and arabinose C₅H₁₀H₅). This stored energy is released when the food is consumed. This demo a dramatic example of the amount of stored energy in sugar. Concentrated sulfuric acid is a strong dehydrating agent and will literally extract the water from the sugar and leave only carbon (Reaction 1). Heat is generated during the dehydration step (–918.9 kJ/mol) and from the dilution of sulfuric acid (–40.6 kJ/mol). Some of the heat is used to convert water into steam.

Reaction 1: C₁₂H₂₂O₁₁(s) → 12C(s) + 11H₂O (–918.9 kJ/mol)

Reaction 2: H₂SO₄(l) → H₂SO₄•nH₂O (–40.6 kJ/mol)