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Thursday, October 22, 2009

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. If you would like to add a procedure or have comments about any of these procedures, please feel free to e-mail me.

Gas Reagents Method Collection Reaction
Ammonia Gently heat a mixture of ammonium chloride and calcium hydroxide in water.
NH3 Ammonium chloride
Calcium hydroxide 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
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+
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
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
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
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
O2 6% Hydrogen peroxide
Manganese dioxide (catalyst) Add hydrogen peroxide to about 5 g of MnO2. Collect over water. 2H2O2 --> 2H2O + O2
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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