Summary Dip tarnished pennies in a vinegar and salt mixture. A chemical reaction makes them instantly shiny! Science content Chemistry: Chemical Changes (2, 7) Lessons activity is in Physical and chemical changes Materials tarnished (dull) pennies or other copper coins paint tray or other small containers vinegar to half fill each well salt, one pinch per well coffee stir sticks or Q-tips Procedure Add vinegar to each students' well of a paint tray, or container. Students to add a pinch of salt and mix in with a stir stick. Students dip half their penny in the vinegar/salt mixture for a few seconds. It will instantly shine up! By only dipping half, they can compare the penny surface before and after shining. Or students can mix the vinegar and salt with a Q-tip, then rub the Q-tip across the penny to make a shiny streak. Then they can immerse their penny in the vinegar/salt to make it completely shiny. Rinse off with water before storing (or it will tarnish again). The chemistry (complex for Elementary): A penny becomes dull as the copper chemically reacts with the oxygen in air 2Cu + O2 -> 2CuO Vinegar separates the CuO molecule again; the salt speeds up this chemical reaction CuO + 2CH3COOH -> Cu(CH3COO)2 + H2O Grades taught Gr 7
