Diffusion and osmosis Why the gas ring between HCl and NH4OH formed where it did
ID: 164163 • Letter: D
Question
Diffusion and osmosis
Why the gas ring between HCl and NH4OH formed where it did.
The following procedure will illustrate the diffusion of gases and the effects of molecular on the relative speeds of diffusion The apparatus consists of a length of glass tubing clamped to a ring stand, cotton and solutions of ammonium hydroxide (NH_4 OH) and hydrochloric acid (HCl). Your instructor will hold some cotton with tweezers and carefully saturate with NH_4OH. Then saturate another piece with HCl. These chemicals will be handled carefully by your instructor. DO NOT ALLOW SKIN CONTACT. WORK UNDER THE HOOD. DO NOT PERMIT THE CHEMICALS TO MIX WITH EACH OTHER AT ANY TIME! Insert the cotton on opposite ends of the glass tube. Simultaneously saturate the two cotton plugs with the appropriate solutions. HCl and NH_4OH react to produce ammonium chloride, which will appear as a white line (precipitate) within the tube. Note the location of this "meeting" between the two chemicals. The weight of HCl gas is about twice that of NH_4OH.Explanation / Answer
Answer:
In this reaction, the gaseous diffusion results the formation of solid white ammonium chloride. A ring of white powder which is ammonium chloride forms near the middle of the tube closer to the hydrochloric acid. This is because the NH4OH is lighter (smaller) than hydrogen chloride and it diffuses more quickly through the air in the tube. Hydrogen chloride has almost twice the molecular weight of NH4OH and hence it takes more time to diffuse than NH4OH. Also the rate of diffusion is inversely proportional to the square root of the molecular mass of the gas. The rate of diffusion is not the same as the speed at which the gas molecules travel (which is hundreds of meters per second).