How to Corrode Cupronickel

Hydrochloric acid is one of aqua regia's components.

Cupronickel is one of the most durable metal combinations, even capable of withstanding immersion in boiling seawater. Therefore, corroding cupronickel requires the use of an extremely caustic acid mixture, often known as aqua regia.

Aqua regia or 'royal water' is a mixture of hydrochloric and nitric acid, capable of dissolving gold, and practically anything else for that matter. Since aqua regia is so powerful, using it requires the utmost caution. However, the results can certainly be spectacular in proportion to the inherent danger.

Things You'll Need

• Safety goggles
• Gloves
• Fume hood
• 60 mL 2M hydrochloric acid (HCl)
• 20 mL 2M nitric acid (HNO3)
• 3 glass beakers
• Glass stir-rod
• Dimes (cupronickel at 8.33% Ni and 91.67% Cu)
• 100 grams sodium bicarbonate (NaHCO3)

Instructions

1. Put on goggles and gloves. Set the three beakers and acid under the fume hood. Pour 60 mL hydrochloric acid in one beaker and pour 20 mL nitric acid in the other.

2. Pour the contents of both beakers into the third beaker. Stir the resulting mixture of acids with the glass rod. Stand away and let the fumes dissipate in the fume hood.

3. 

   Dimes, nickels, and quarters are all made of cupronickel.

   Gently place the dimes into the aqua regia, as to not splash the acid. Allow the beaker to sit for 3 or 4 minutes for visible signs signs of corrosion. You will see the dimes fizz as the reaction takes place.

4. Add 100 grams of sodium bicarbonate to the mixture after the reaction has completed. Let the mixture sit for 5 minutes, or until the acid has completely been neutralized. The resulting liquid can now be safely disposed of.

Tips & Warnings

• Increasing the concentration (molarity) of the acids will increase the speed of corrosion, but the aqua regia will also be more dangerous.

• Aqua regia is extremely dangerous! The liquid acid is corrosive and can cause burns while the vapor may irritate the respiratory tract. It is also unsafe to store.

References

• Va Tech - Lab for Scientific Visual Analysis: The Copper-Nickel Application
• Princeton University - Environmental Health & Safety: Aqua Regia
• United States Mint: Coin Specifications