Electroplating. OBJECTIVES: Visitors learn how metals that conduct electricity can be coated with other metals. Observing Investigating Inferring

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1 EXPERIMENT Electroplating Visitors plate zinc onto brass brads and other metal objects. OBJECTIVES: Visitors learn how metals that conduct electricity can be coated with other metals. SCIENCE TOPICS PROCESS SKILLS VOCABULARY Electricity Properties of Metals Properties of Ions Atomic Structure Observing Investigating Inferring Atom Electron Electroplating Ion Metal Solution Unit 5 Industrial Chemistry U5.1

2 Electroplating Procedure: 1. Always wear safety goggles. 2. Clip a clean brass fastener to the end of the red wire. 3. Hold one wire in each hand at the place marked with yellow tape. Find the plastic tub filled with zinc sulfate (ZnSO 4 ) solution. Place the black wire with zinc metal into one end of the plastic tub. Place the wire with the brass fastener into the other end of the tub so that the fastener is about half covered by solution. DO NOT touch the wires together and DO NOT put your fingers in the solution. 4. Hold the wires in place for about 45 seconds. 5. Remove the wires from the solution and briefly dip the ends of both wires into the beaker of rinse water. Look closely at the brass fastener. Do you notice any change in the fastener? You have zinc plated the fastener! 6. Put the fastener in the cup labeled Used Metals. Try the experiment again with other metals. Are your results the same or different? 7. Rinse and put all used metals in the Used Metals cup. Wash your hands in the sink OMSI

3 How did the zinc get on the brass fastener? A Closer Look: In this experiment, an electrical current from the battery flows through the fastener and the solution. Zinc ions (positively charged zinc atoms) in the solution are attracted to the fastener at the negative terminal of the battery. When the zinc ions hit the fastener, they are supplied with electrons from the battery and are turned into a solid zinc coating. This process is called electroplating. Electroplating is used in industry to coat one metal (e.g., iron, zinc, steel) with another metal (e.g., zinc, copper, silver). Only an electrically conducting metal can be plated in this way. Electroplating is often done to protect a metal from rust; for example, zinc is used to protect iron. Electroplating also is used to enhance the appearance of metal objects; for example, some jewelry is coated with gold OMSI

4 See Materials Prep for more details (with amounts to have on hand) Three plastic cups One rectangular plastic tub approximately 5 in. long, 4 in. wide, and 2 in. high One piece of aluminum foil (large enough to cover the tub) One 250-ml beaker One 6-volt lantern battery (keep two fresh batteries on hand) Two heavy-duty alligator clips attached to both ends of a red insulated wire about 1 ft (30 cm) long (keep spare on hand) One alligator clip attached to one end of a black insulated wire about 1 ft (30 cm) long (keep spare on hand) About 150 g of ZnSO 4 (zinc sulfate) (keep 500 g on hand) CuSO 4 5H 2 O (copper sulfate) (optional) (keep 500 g on hand) 50 brass paper fasteners (keep on hand) 50 assorted metals (screws, paper clips, nails, keys, pennies, etc.) (keep on hand) Zn (zinc) metal strip (2 in. by ⅜ in.) (keep a few spare pieces on hand) Wire strippers (from general storage) One voltmeter (from general storage ) Electrician s tape One or two 500-ml storage bottles Setup/Takedown Procedures Label the rectangular container Zinc Sulfate (ZnSO 4 ) Solution. Label the beaker Rinse Water. Label the three plastic cups Brass Fasteners, Used Metals, and Other Metals. Cut Zn (zinc) metal strips (2 in. by ⅜ in.). Strip 1 in. of one end of the red wire (the end without the alligator clip). Wrap the wire through the hole of the zinc strip. Secure the metal strip with electrician s tape. Attach one clip of the black wire to the negative terminal of the battery. Attach one clip of the red wire to the positive terminal of the battery. Use electrician s tape to secure both wires to the battery terminals and to cover all exposed metal. Make handles with electrician s tape about 3 in. from the loose end of each wire. U1.24 Unit 5 Industrial Chemistry

5 Make sure the labeled container, cups, Zn (zinc) strips, assorted metals, brass paper fasteners, battery, and wires are in good working order (see Original Setup). Prepare ZnSO4 (zinc sulfate) solution as needed (see Materials Prep). Place the lab voltmeter in the experiment tub. Set out the visitor instructions in a Plexiglas holder. Set out the following on a tray: Labeled rectangular tub Three labeled plastic cups Labeled beaker Battery with attached wires Pour about 50 ml of ZnSO 4 (zinc sulfate) solution into the rectangular container. (The solution should cover the bottom to a depth of at least ¼ in.). Put the brass fasteners and other metals in the appropriate cups. Fill the beaker with fresh water. Replace the brass fasteners after a few uses. Replace the assorted metals as they corrode. Using a voltmeter, check the voltage on the battery-it should be close to 6 volts. Try the experiment. If you do not see significant plating in 45 seconds, pour the ZnSO 4 (zinc sulfate) solution down the drain with plenty of water. Refill the rectangular container with about 50 ml of fresh solution. Rinse the water beaker. Cover the ZnSO 4 (zinc sulfate) container with aluminum foil. Recycle the used metal by soaking it in vinegar overnight or by soaking it in 1M HCl for 1 to 2 minutes. Replace the metal pieces when they begin to corrode. Return the equipment to the tub. Store the tub and instructions under the counter. Discard the ZnSO 4 (zinc sulfate) solution in the tub by rinsing it down the drain with plenty of water. Return the voltmeter to general storage. Unit 5 Industrial Chemistry U1.25

6 Clean the tray and leave it at the station. Clean all equipment and return it to the tub. Visitors can try plating their own objects (keys, coins, etc.). Make sure they rinse the metals well before taking them home. Check the setup periodically to ensure that the wires are out of the solution and are not touching each other (otherwise the battery will run down quickly). You can use the waste HCl from rocket science to clean Zn off keys to reuse. To do this, place keys in a beaker with waste HCl just barely covering them overnight. When keys turn reddish, recycle them (they are no longer reusable). Visitors can reverse plate the piece of metal by attaching the black wire (with zinc metal) to the negative terminal and the red wire (with the object) to the positive terminal. Ask visitors what they would need to copper-plate something. They can even try it if you provide them with 1.0M CuSO 4 (copper sulfate) solution. ZnSO 4 (zinc sulfate) and CuSO 4 (copper sulfate) are hazardous substances; follow handling and disposal instructions. Consult the Material Safety Data Sheets (MSDS) for additional information. U1.26 Unit 5 Industrial Chemistry

7 To prepare 1.0M ZnSO 4 (zinc sulfate) solution: Wearing a lab coat, protective eyewear, and gloves, weigh g ZnSO 4 7H 2 O (or 89.8 g ZnSO 4 1H 2 O) Add to 500 ml H 2 O Store the solution in a labeled/dated plastic bottle. To prepare (for Extensions only) 1.0M CuSO 4 (copper sulfate) solution: Wearing a lab coat, protective eyewear, and gloves, weigh 125 g CuSO 4 5H 2 O. Put the CuSO 4 5H 2 O into a beaker of 500 ml dh 2 O (deionized water). Mix the solution. Store the solution in a labeled/dated plastic bottle. Unit 5 Industrial Chemistry U1.27