making+brass

//All you need are a couple of common chemicals to turn your normal copper pennies (or other mainly-copper object) from copper to silver and then to gold. No, the coins won’t really be silver or gold. The actual metal involved is zinc. This project is easy to do.// __ Materials Needed: __
 * Making Brass **
 * = [[image:flammable.jpg width="175" height="178"]] ||= [[image:corrosive.jpg width="191" height="181"]] ||
 * = Hexane is **HIGHLY FLAMMABLE** ||= Sodium hydroxide is **CORROSIVE** ||
 * Copper penny*
 * Zinc granules
 * 2 M Sodium hydroxide solution **CORROSIVE**
 * tweezers or tongs
 * container of water
 * Bunsen burner, heat proof mat & tripod
 * Boiling tube
 * 100 ml beaker
 * 250 ml beaker for water bath
 * Hexane ** HIGHLY FLAMMABLE **
 * Goggles should be worn when handling sodium hydroxide - for a safer alternative read below:

As a safer and legal alternative you can replace the coin with a length of thick copper wire that can hang inside a test tube. This will use less chemicals and make extracting the copper object easier. //*After 1992, 1p coins were made of copper-plated mild steel - we will have to make sure coins are copper.// //Until 1992, 1p coins were made of brass.// //It is illegal to deface coins of the realm so it is suggested you used copper-based foreign currency.// __How to Make Silver Pennies:__ WEAR EYE PROTECTION AT ALL TIMES
 * 1) Start heating water in a 250 ml beaker over a Bunsen burner.
 * 2) Clean your penny by dabbing with //hexane// ** HIGHLY FLAMMABLE **
 * 3) Once //hexane// has evaporated, immerse penny in //sodium hydroxide// solution ** CORROSIVE ** that has been added to an evaporating basin.
 * 4) Take penny out with tongs and rinse in water and put to one side
 * 5) Place a 250 ml beaker on a gauze on top of a tripod. Add a thermometer, fill with water and heat with a Bunsen burner.
 * 6) Add some small //zinc granules// and your penny into the boiling tube. Add enough //sodium hydroxide// ** CORROSIVE ** to cover.
 * 7) Once the water is near-boiling add your boiling tube to the beaker of water, taking the heat away.
 * 8) Stir boiling tube with glass rod making sure coin touches with //zinc//.
 * 9) Wait 5-10 minutes and note a colour change of the coin, then pour contents into a small beaker, use tongs to remove the pennies from the solution.
 * 10) Rinse the pennies in water, then set them on a towel to dry. You can examine the pennies once you have rinsed them.

//This chemical reaction plates the cooper in the penny with zinc. This is called galvanization.// //The zinc reacts with the hot sodium hydroxide solution to form soluble sodium zincate, which is converted to metallic zinc when it touches the surface of the penny.// __How to Make the Silver Pennies turn Gold:__
 * 1) Grasp a silver penny with tongs.
 * 2) Gently heat the penny in the outer (cool) part of a burner flame. Alternatively you can leave the coin on the warm gauze.
 * 3) Remove the penny from heat as soon as it changes colour.
 * 4) Rinse the gold penny under water to cool it.

Heating the penny fuses the zinc and copper to form an alloy called brass.

Brass is a homogeneous metal that varies from 60-82% Cu and from 18-40% Zn. Brass has a relatively low melting point, so the coating can be destroyed by heating the penny for too long. __The theory is as follows:__

The coating of zinc gives the impression that the coin is now coated with silver.

On heating the coin in the Bunsen flame, brass is formed by the zinc migrating into the surface layer of the copper. This gives a gold appearance to the coin.

Brass is an alloy of copper containing between 18% and 40% of zinc.

A similar zinc plating process is used industrially, but with cyanide ions rather than hydroxide ions as the complexing agent.

The reaction between zinc and sodium hydroxide to form sodium zincate is as follows:

Zn(s) + 2NaOH(aq) + 2H2O(l) → Na2[Zn(OH)4](aq) + H2(g)

The plating reaction involves an electrochemical cell; it will not take place unless the copper and the zinc are in contact, either directly (as here) or by means of a wire. // The electrode reactions are: // At the zinc electrode: Zn(s) → Zn2+(aq) + 2e– followed by complexing of the zinc ions as  [Zn(OH)4]2–(aq) At the copper electrode : [Zn(OH)4]2–(aq) + 2e– → Zn(s) + 4OH–(aq)