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How to Prepare Gases

Chemistry Lab Instructions

You can use common chemistry lab chemicals and equipment to prepare several gases. A conical flask, thistle funnel, delivery tube, pneumatic trough, and beehive are useful items to have on hand. Please make sure you are familiar with the use and functioning of the laboratory equipment you use, are aware of the characteristics of the substances (toxicity, flammability, explosivity, etc.), and take proper safety precautions. Use a ventilation hood (fume cupboard) and keep flammable gases away from heat or flame. I've tried to be as accurate as possible in my instructions, but you use them at your own risk. For convenience, I've listed the gases in alphabetical order.

Gas Reagents Method Collection Reaction
Ammonia
NH3
Ammonium chloride

Calcium hydroxide
Gently heat a mixture of ammonium chloride and calcium hydroxide in water. Upward displacement of air in a hood. Ca(OH)2 + 2NH4Cl → 2NH3 + CaCl2 + 2H2O
Carbon Dioxide
CO2
Calcium carbonate (marble chips)
5 M Hydrochloric acid
Add 5 M hydrochloric acid to 5 - 10 g marble chips. Upward displacement of air in a hood. 2HCl + CaCO3 → CO2 + CaCl2 + H2O
Chlorine
Cl2
Potassium permanganate
Conc. Hydrochloric acid
Add concentrated hydrochloric acid dropwise onto a small amount of potassium permanganate crystals (in flask). Upward displacement of air in a hood. 6HCl + 2KMnO4 + 2H+ → 3Cl2 + 2MnO2 + 4H2O + 2K+
Hydrogen
H2
Zinc (granulated)
5 M Hydrochloric acid
Add 5 M hydrochloric acid to 5 - 10 g granulated zinc pieces. Collect over water. 2HCl + Zn → H2 + ZnCl2
Hydrogen Chloride
HCl
Sodium chloride
Conc. Sulfuric acid
Slowly add concentrated sulfuric acid to solid sodium chloride. Displacement of air in a hood. 2NaCl + H2SO4 → Na2SO4 + 2HCl
Methane
CH4
Sodium acetate (anhydrous)
Soda lime
Mix 1 part sodium acetate with 3 parts soda lime. Heat in a dry pyrex test tube or flask. Collect over water. CH3COONa + NaOH → CH4 + Na2CO3
Nitrogen
N2
Ammonia
Calcium hypochlorite (bleaching powder)
Shake 20 g calcium hypochlorite into 100 mL water for several minutes, then filter. Add 10 mL conc. ammonia and heat mixture. Use extreme caution! Chloramine and explosive nitrogen trichloride may be produced. Displacement of air. 2NH3 + 3CaOCl2 → N2 + 3H2O + 3CaCl2
Nitrogen
N2
Air
Lighted Phosphorus (or heated Fe or Cu)
Invert a bell jar over lighted phosphorus. Oxygen and phosphorus combine to form phosphorus pentoxide, which is absorbed by the water over which the bell jar stands (may be violent reaction), producing phosphoric acid and leaving the nitrogen behind. Removal of oxygen. 5 O2 + 4 P → P4O10
Nitrogen Dioxide
NO2
Copper (turnings)
10 M Nitric acid
Add concentrated nitric acid to 5 - 10 g copper. Upward displacement of air in a hood. Cu + 4HNO3 → 2NO2 + Cu(NO3)2 + 2H2O
Nitrogen Monoxide
NO
Copper (turnings)
5 M Nitric acid
Add 5 M nitric acid to 5 - 10 g copper. Collect over water. 3Cu + 8HNO3 → 2NO + 3Cu(NO3)2 + 4H2O
Nitrous Oxide
N2O
Sodium nitrate
Ammonium sulfate
Mix 10 g powdered sodium nitrate and 9 g ammonium sulfate. Heat well. Displacement of air. NH4NO3 → N2O + 2H2O
Oxygen
O2
6% Hydrogen peroxide
Manganese dioxide (catalyst)
Add hydrogen peroxide to about 5 g of MnO2. Collect over water. 2H2O2 → 2H2O + O2
Oxygen
O2
Potassium permanganate Heat solid KMnO4. Collect over water. 2KMnO4 → K2MnO4 + MnO2 + O2
Sulfur Dioxide
SO2
Sodium sulfite (or sodium bisulfite)
2 M Hydrochloric acid
Add dilute hydrochloric acid to 5 - 10 g sodium sulfite (or bisulfite). Upward displacement of air in a hood. Na2SO3 + 2HCl → SO2 + H2O + 2NaCl
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