Activity

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)
Half the penny shined
Stripe of shine on a penny
Shined pennies
Lessons activity is in
Mixtures, Physical and chemical changes
Chemical reactions
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

Notes

I use this chemical reaction to restore tarnished copper wire ends of bulbs and wires used in the electric circuits activity.
When it becomes hard to make a connection (the wires have to be pushed together) I clean all my bulbs and wires in this way, then rinse and dry completely.

Grades taught
Gr 2
Gr 3
Gr 7