Experimental Apparatus
Collection Method
Water displacement: Gas is collected over water. Works for gases that are insoluble in water (e.g., H₂, O₂). The gas displaces water in an inverted cylinder.
Gas Type
Reaction Parameters
Gas Preparation Equations
What is Gas Preparation?
Gas preparation in the laboratory involves generating specific gases through chemical reactions and collecting them using appropriate methods. Common gases include hydrogen (H₂), oxygen (O₂), carbon dioxide (CO₂), and others. The choice of preparation method depends on the gas's physical properties like solubility in water and density relative to air.
Experimental Apparatus
Reaction Flask: Contains the solid reactant and receives the liquid reagent. Equipped with a thistle funnel and delivery tube.
Delivery Tube: Transports gas from flask to collection vessel. Must be airtight.
Collection Methods: Water displacement (insoluble gases), upward air displacement (lighter gases like H₂), downward air displacement (heavier gases like CO₂).
Collection Method
Water Displacement: For gases insoluble in water (H₂, O₂, N₂). Gas collected in inverted cylinder filled with water.
Upward Air Displacement: For gases lighter than air (H₂, NH₃). Collection vessel inverted.
Downward Air Displacement: For gases heavier than air (CO₂, O₂, Cl₂). Collection vessel upright.
Production Rate and Kinetics
Gas production rate depends on several factors according to chemical kinetics.
Concentration: Higher reactant concentration increases collision frequency (r = k[A]ⁿ).
Temperature: Higher temperature increases kinetic energy and activated molecules (Arrhenius: k = A·e^(-Ea/RT)).
Surface Area: Greater surface area exposes more reaction sites for solid-liquid reactions.
Catalyst: Lowers activation energy, increases rate without being consumed.
Common Laboratory Gases
Hydrogen (H₂): Zn + H₂SO₄ → ZnSO₄ + H₂↑. Colorless, odorless, extremely flammable. Lightest gas (0.09 g/L). Insoluble. Collected by water or downward air displacement.
Oxygen (O₂): 2KClO₃ →[MnO₂] 2KCl + 3O₂↑. Colorless, odorless, supports combustion. Slightly soluble. Collected by water displacement.
Carbon Dioxide (CO₂): CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑. Colorless, odorless, heavier than air (1.98 g/L). Moderately soluble. Collected by upward air displacement.
Safety Precautions
Hydrogen: Extremely flammable and explosive (4-75% in air). Keep away from flames.
Oxygen: Supports combustion. Keep away from flammable materials.
Carbon Dioxide: Can cause asphyxiation in high concentrations.
General: Wear safety goggles and gloves. Work in fume hood. Check for leaks.
Applications of Prepared Gases
Hydrogen: Fuel cells, hydrogenation, reducing agent, rocket fuel, ammonia synthesis.
Oxygen: Medical respiration, steelmaking, chemical oxidation, wastewater treatment.
Carbon Dioxide: Carbonation, fire extinguishers, greenhouse gas, refrigerant (dry ice), welding atmosphere.