Copper Coin Alloy 

Create coins of gold!.

 

 

 

Category - Chemicals & Reactions

Key Idea - Metals & Non-Metals

 

Purpose - Enables students to be able to create their own metal alloy.
Nature -  Class Practical (Senior Students)
Materials -  250 ml beaker, Bunsen burner, tripod, gauze mat, tongs, steel wool, three copper coins, 1M hydrochloric acid, 3M sodium hydroxide, granulated zinc
Method - 
  1. Clean the copper coins to a bright shine by soaking them in hydrochloric acid few a couple of hours, then rinsing and scrubbing with steel wool.
  2. Set up the burner, trip pod and gauze mat and heat the beaker containing 150 ml of sodium hydroxide and a handful of granulated zinc.
  3. When boiling, toss in two of the copper coins and boil for about 10 minutes,  Use the tongs to remove from the beaker and rinse in fresh water.  You should find that the coins are covered in a layer of zinc.
  4. Using the tongs, hold one of the coins in the hottest part of the burner flame for three minutes.
  5. Compare the three coins; you should find the one is a shiny copper colour, one is a silver colour and one is a shiny gold colour. 
Safety - 3M NaOH  is quite strong so care should be taken with it's use.  Care should be taken to avoid burns on hot apparatus. 
Explanation -

The boiling stage of the practical creates a zinc coating on the copper coin that will wear away over time.  

A Bunsen burner flame is about 1600º C at its hottest point, while copper melts at around 1100º and zinc at about 420º.  So when you put the coated coin into the flame the two metals melt together to form the alloy brass.  This alloy coated coin will probably never wear away to reveal the copper centre. 
Notes - It should probably be noted that it is illegal in most countries to deface legal currency.  The now unused 1 and 2 cent pieces in Australia are perfect for this practical.