In the Classroom

This activity involves the use of chemicals. We strongly discourage this activity from being performed by anyone other than a trained chemist. Science Discipline(s) Chemistry This activity is best conducted at the middle school or high school level. Topics Reduction, oxidation, metal alloys Activity Title Gold and Silver Pennies Materials Bunsen burner

• 20 mL of 3M NaOH
• 0.1 g zinc dust
• Evaporating dish
• Hot plate
• Tongs
• 200 mL beaker of water
• Pennies
• Steel wool

Procedure

1. Put zinc dust in the evaporating dish.
2. Add 20 ml of NaOH solution to the dish on top of the zinc
3. Set hot plate to medium heat and place evaporating dish on top.
4. Use steel wool two polish two or more pennies.
5. After five minutes of heating on the hot plate. Place the clean penny in the solution until it has been fully coated with zinc and turns silver.
6. Remove the penny from the dish with tongs and place it in water. When penny has cooled down, clean it with a cloth to remove excess zinc.
7. To turn it gold, place penny in the flame of the Bunsen burner until it turns gold. It is possible to also use a hot plate to heat the pennies to avoid an open flame. (Do not over heat)
8. Place penny somewhere safe to cool.

Questions What variables do you believe are important in this activity?  How could you design an experiment to test your hypothesis regarding which variables are important in the activity? What are alloys? List two uses of alloys. Why do metals become damaged when exposed to the environment?  Can you  think of other examples of metal objects that have become damaged by the environment? Metal bridges are made out of steel.  Why do you think that it is important that the paint on a bridge covers all exposed steel? Galvanized metal is iron that is coated with a thin layer of zinc.  What do you think the role of the Zinc is? What is the alloy in this lab that you will be making?   Explanation It is highly recommended for the teacher to do this activity for students for middle school students. High school and college level students can perform this experiment with proper safety techniques. Next Generation Science Standards PK – grade 3 students : K-LS1-1; 1-LS1-1; 1-LS1-2; RI.1.1; RI.1.2;RI.1.10; W.1.7; 2-PS1-1; 2-PS1-2; 2-PS1-3; 2-PS1-4; RI.2.1; RI.2.3; RI2.8; RI.2.7; MP.2; MP.10 Grade 4 – 6 students: 4-PS3-4; 4-PS3-3; 4-PS3-3; W.4.7; 5-PS1-1; 5-PS1-2; 5-PS1-3; 5-PS1-4; W.5.7; W.5.8; MP.5; MP.2 Middle school students: RST.6-8.3; 6.RP.1; MS-PS1-1; MS-PS1-2; MS-PS1-3; MP-PS1-4; MP-PS1-5; MP-PS1-6; RST.6-8.3; RST.6-8.7