Chemistry Feb. 5 & 8, 2016

•OBJECTIVE: Students will describe and explain orally and in writing how alloys are formed by completing a lab activity.

•W.O.D. Travesty-a grossly inferior imitation.

•WARM-UP

1. Obtain a copy of the lab handout and write a summary of the lab procedures in your own words.

HW

•Complete a lab report for the penny lab.

Lab handout

Gold penny lab

Introduction

Have you ever turned an ordinary penny into silver and then into gold? Get rich quick by following this short and simple procedure.

In this reaction, sodium zincate (which is silver) is formed by heating elemental zinc with sodium hydroxide solution.

Zn_(s)  +  2NaOH_(aq)     Na₂ZnO₂(aq)   + H_2(g)

When the zinc-coated penny is heated, the penny becomes gold in color. The gold color is due to the zinc and copper melting together to form brass. Brass is a copper-zinc alloy.

Procedure

1.     The pennies have already been clean so DO NOT TOUCH THE PENNY WITH YOUR FINGERS. Using a pair of tongs, remove your penny from the solution and place it on a piece of clean napkin until you are ready to use it.

2.     Weigh out 0.5 grams of granulated zinc and place it in a evaporating dish. Add 25 ml of 3M sodium hydroxide solution (NaOH). Use caution when handling sodium hydroxide as it can cause burns.

3.     Using a ring stand set up with a Bunsen burner, GENTLY heat the mixture to steaming. DO NOT ALLOW THE SOLUTION TO BOIL OR SPLATTER.

4.     Using a pair of clean tongs, place the penny into the hot mixture. Wait until the penny is completely silver.

5.     Using a pair of tongs remove carefully and place into a beaker containing some water. Shine the penny with a piece of paper.

6.     Using a pair of tongs, hold the penny by the edges and hold the burner flame until the penny is gold (about 5-10 seconds). Place the golden penny into the beaker of cold water, wait a few minutes before handling the penny.

Conclusion questions

1.     Did you make real silver? Explain why the penny turned silver.

2.     Did you make real gold? Explain why the penny turned gold.

3.     What are advantages of using alloys over pure element??