Сlean a penny in 60 seconds
Vinegar and salt – and an old copper coin shines like new!
Warning! Only under adult supervision.
- table salt;
- old copper coin.
Dissolve two tablespoons of table salt in a glass of vinegar. Pour the solution into a bowl and immerse an old copper coin in it – it brightens rapidly before your eyes!
Old copper coins are covered with films of a mixture of copper(I) oxide and copper(II) oxide. Such films cannot be dissolved in vinegar or a solution of sodium chloride separately, but they rapidly react with a mixture of vinegar and salt. Copper(II) oxide dissolves in acetic acid, forming copper(II) acetate:
2CH₃COOH + CuO → (CH₃COO)₂Cu + H₂O
And copper(I) oxide reacts with sodium chloride, forming chloride complexes:
Cu₂O + 2NaCl + 2CH₃COOH → 2Na[CuCl₂] + 2CH₃COONa + H₂O
These processes must happen simultaneously, so the coin cannot be cleaned by rinsing first with vinegar, then with a salt solution, or vice versa. Rinse your coin with water after the experiment to ensure that it retains its shine for a long time!
Many more cool experiments await you in the MEL Chemistry subscription!