TURTLE ROCK SCIENTIFIC / SCIENCE PHOTO LIBRARY TURTLE ROCK SCIENTIFIC / SCIENCE PHOTO LIBRARY
Collecting hydrogen gas over water. Zinc metal (Zn) coils are placed in an Erlenmeyer flask with 1 M sulfuric acid (H2SO4). Hydrogen gas (H2) is produced in the reaction: Zn + H2SO4 -> ZnSO4 + H2. Hydrogen gas is lighter (less dense) than air and does not dissolve in water. Therefore it can be collected in an inverted test tube by displacing water. This method is called collection over water.
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