2. Tina Michetti tinamichetti@hotmail.com INSTITUT DON BOSCO Avenue du Val d’Or, 90 d 1150 Bruxelles

4. Adrien Mégane Nicolas Corentin Benjamin Walid Chahid Hugo Adnane David

5. Original coin Zinc coated coin Brass coated coin

6. This little experiment of chemistry will do wonders in a few minutes! The effect is spectacular. You ’ ll treat a coin containing copper (parts 1, 2, or 5 cents euro) with zinc and then form an alloy, brass.

7. Subject area : Chemistry Other subjects involved : Physics, Maths Age of the students : 12 to 14 Topic : Properties of chemical elements Density concept Content involved :Chemicals elements, compounds, alloys, brass, mass, volume, density Student skills involved :-Experimental work -Capacity to observe -Capacity to work as a group - Capacity to have recourse to different methods and tools to solve a problem -Communication skills. Aims :Development of experimental skills to arouse interest in sciences

8. sodium chloride vinegar powdered zinc three coins of 1,2 and 5 EuroCent sodium hydroxyde ( 4M) distilled Water hot plate 100-mL beaker (2) tweezers gas burner soft tissue paper balance 100 ml graduated cylinder

9. 1.Clean the copper coins : Place a tea spoon of sodium chloride it in a clean 100-mL beaker. Add 20 mL of vinegar and stir. Place the 9 coins in the sodium chloride/acetic acid mixture and stir until they are shiny. Remove the coins after they are clean. Wash the coins well with water and dry them with a towel.

10. 2. Weigh the 9 coins and record the mass 3. Fill a 100 ml beaker with 50 ml of a solution of sodium hydroxyde (c= 4 mol/l) and add some powdered zinc. 4. Put the mixture on a hot plate and heat it until it starts simmering. 5. Drop the coins into the hot alkali.

11. 6. After 1 – 2 minutes, take the now silvery coins out of the alkali using tweezers and wash off the excess zinc and hydroxide solution with water. The coins appeared covered with brilliant silver. 7. It is of course a layer of zinc. 8. Wash and polish the coins very carefully using some soft tissue paper. 9. Dry the 9 silvered coins and record the mass

12. 10. Using a pair of long tweezers, heat the dry and polished coin very shortly (a few seconds) in a flame of a gas burner. Immediately the pieces change colour up to a beautiful golden color. The pieces appear to be gold ! In fact you have create a copper and zinc alloy, brass. By heating the coin in a flame of a gas burner, the thin layer of zinc and copper just below form a golden brass alloy

13. 11.Cool the coins under running water, dry and polish them with a towel. 12.Weigh the 9 golden coins and record the mass Mass of the 9 clean, dry coins ____________ g Mass of the 9 clean, dry, silvered coins____________ g Mass of the 9 clean dry, gold coins ____________ g

14. Do you have really turned copper into gold? Let’s calculate the density Formula : Density = Mass/ Volume (Mass in gr; Volume in ml) To calculate the density we need to know the mass (gr) and the volume (mL) The mass we have mesured but what about the volume? How do you mesure the volume of the coins ? When measuring for the volume you need a 100ml graduated cylinder. Fill the graduated cylinder up to 50 ml Put the 9 golden coins into the cylinder and get the reading in milliliters (mL). Now subtract the old reading by the new reading and you have the volume of the 9 golden coins in milliliters. (If you want to convert the milliliters into cubic centimeters, just remember this: 1 cubic centimeter = 1 milliliter) Calculate the density and compare with the table below. You can see that you haven’t changed the copper into gold! You can proceed in the same way to see that the silvered coins are not real silver! You can also check if the original coins are made with pure copper. Metal Density in g/mL Copper 8.92 Zinc 7.14 Silver 10.5 Gold 19.3

16. SAFETY PRECAUTIONS Goggles or safety glasses must be worn at all times in the laboratory. Do not allow the sodium hydroxide solution in this experiment to actively boil. Sodium hydroxide is caustic and may splatter causing severe damage to the skin or eyes. In case of contact, wash it off immediately with cold water for at least 10 minutes and then, if it is necessary, get medical help immediately. DISPOSAL The sodium hydroxide solution should be placed in the appropriate waste container. The zinc metal can be reused. The zinc should be rinsed with water and placed in the appropriate container supplied in the laboratory. Do not pour any zinc metal down the drain.