Teachers can educate students on the nature of different metals by collecting dirty coins and comparing their ability to be cleaned by a combination of salt and vinegar. Prepare the cleaning solution by preparing four beakers with 1 tsp. of salt stirred in 1/4 cup of white vinegar until the salt dissolves. Place a penny, nickel, dime and quarter in the beakers and leave for 5 minutes. When the time is up, observe the results. Identify which coin appears cleanest and whether any appear unaffected. Discuss the metallic composition of each coin type and encourage students to propose theories as to why salt and vinegar cleans some metal types better than others.
While some elements effectively accomplish certain tasks on their own, compounds and mixtures are often essential for producing chemical reactions that are more successful in completing the same functions. Prepare three beakers: Place 1 tsp. of salt in the first beaker and add 1/4 cup of distilled water; place 1/4 cup of white vinegar in the second beaker and prepare a third beaker with a mixture of 1 tsp. of salt dissolved in 1/4 cup of white vinegar. Locate three pennies that appear equally dirty and place one in each of the beakers. Leave for 15 minutes before observing the effect of each cleaning agent on the penny. Teachers should discuss why the chemical reaction between the salt and vinegar in beaker #3 yields a cleaner penny than either substance alone in the first two beakers.
Instructors should introduce the concept of oxidation reactions by discussing the effects of oxygen atoms combining with other atoms to form layers on metal such as rust or copper oxide. Submerge 20 dirty pennies in a bowl containing 1 tsp. of salt dissolved in 1/4 cup of white vinegar and leave for 5 minutes. Remove half of the pennies from the solution and rinse with distilled water before placing on a paper towel. Remove the remaining pennies and set on a towel without rinsing. Leave for one hour. The unrinsed pennies should appear blue-green in color. Discuss the combination of copper atoms with oxygen and chlorine to form malachite and present pictures of the Statue of Liberty for a cross-curricular discussion of science and social studies.
Pennies made prior to 1982 contained a 95% concentration of copper. After that time, the rising price of copper resulted in the production of pennies that are 97.5% zinc with a thin copper coating to achieve the same appearance. Collect 20 pennies made from 1983 until today and then collect 20 pennies with a date stamp of 1982 or earlier. All pennies should appear similar in the amount of copper oxide and accumulation of dirt. Place the modern pennies in a container filled with a solution of 1 tsp. salt dissolved in 1/4 cup vinegar and place the older pennies in a second container that has an identical solution. Observe after 10 minutes to determine if the concentration of copper in the coin influences the cleaning ability of the salt and vinegar mixture.