What gas is produced when copper is added to diluted HCl?

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SUMMARY

The reaction of copper with diluted hydrochloric acid (HCl) produces hydrogen gas (H2) and may also release HCl gas, which can irritate the eyes. The presence of bubbles on the copper pennies indicates hydrogen gas formation, while the equilibrium concentration of copper ions (Cu2+) in non-oxidizing acid is minimal, suggesting that this is not the primary cause of bubble formation. Additionally, if copper carbonate is present, carbon dioxide (CO2) could also be produced, but the primary gas observed is hydrogen.

PREREQUISITES
  • Understanding of acid-base reactions, specifically with hydrochloric acid.
  • Knowledge of gas evolution in chemical reactions.
  • Familiarity with copper chemistry and its reactions with acids.
  • Basic grasp of equilibrium concepts in chemistry.
NEXT STEPS
  • Research the properties and reactions of hydrochloric acid with metals.
  • Learn about gas evolution reactions, particularly involving hydrogen and carbon dioxide.
  • Study the formation and properties of copper carbonate and its reactions.
  • Explore equilibrium concentrations in chemical reactions involving non-oxidizing acids.
USEFUL FOR

Chemistry students, educators, and professionals interested in acid-metal reactions, gas evolution, and the behavior of copper in acidic environments.

SDTK
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Copper pennies were placed into HCl which had been diluted with an unknown quantity of water.

The pennies look cleaner, ... remain un-corroded (as expected). There is a slight bit of gas being produced , with no smell, but can cause discomfort to eyes. Bubbles formed on the pennies for the first 2 days.

-- What is the gas?

-- Could it be a product of reaction with the HCl and any oils, "dirt" that was on the pennies?
 
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If it causes discomfort to the eyes, it is not hydrogen. That only leaves one possibility...
 
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Some HCl may come out from solution as HCl gas which may irritate your eyes. The gas from bubbles you saw happening might be Hydrogen gas, H2.

Cu + 2H+ ---------> Cu+2 + H2
 
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Equilibrium concentration of Cu2+ in the presence of non-oxidizing acid is in the 10-11 M range, I don't think that's enough for the bubble formation.
 
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symbolipoint said:
Some HCl may come out from solution as HCl gas which may irritate your eyes. The gas from bubbles you saw happening might be Hydrogen gas, H2.

Cu + 2H+ ---------> Cu+2 + H2
thank you
 
Borek said:
Equilibrium concentration of Cu2+ in the presence of non-oxidizing acid is in the 10-11 M range, I don't think that's enough for the bubble formation.
thank you
 
It could be carbon dioxide if some copper carbonate had formed on the coins as a result of corrosion.
 

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