Shining pennies

Summary

Dip tarnished pennies in a vinegar and salt mixture. A chemical reaction makes them instantly shiny!

Science content

Chemistry: Chemical Changes (2, 7)

Science competencies (+ questioning + manipulation + others that are in every activity)

Processing/analyzing: classifying data, finding patterns (1 up)

Processing/analyzing: considering alternative explanations (5 up)

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
The combination of vinegar (a weak solution of acetic acid), and table salt (sodium chloride) helps to dissolve the
copper oxide. (https://www.acs.org/content/dam/acsorg/education/outreach/ncw/plan-an-e…)
Vinegar separates the CuO molecule again; the salt speeds up this chemical reaction
CuO + 2CH3COOH -> Cu(CH3COO)2 + H2O

Idea:
Demo to students then ask them what they think happened.
Home in.... (simiiar to air resistance dropping plates demo).

Grades taught

Gr 7

Activity