92 DIFFUSION 



2. Temperature. — The kinetic activity, and hence the rate of diffusion 

 of solute molecules, increases with increase in temperature. 



3. Diffusion Gradient. — The steeper the diffusion gradient, the more 

 rapidly solute particles diffuse. 



4. Solubility. — In general, the more soluble a substance is in a liquid, 

 the more rapidly it will diffuse through that liquid. This influence of solubility 

 upon diffusion rates can be interpreted principally in terms of its effect upon 

 the diffusion gradient, since obviously steeper gradients can be built up if the 

 solute is very soluble in the liquid than if it is only slightly soluble. 



Discussion Questions 



1. Why, in an experiment in which copper sulfate crystals are put in the bottom 



of a tall cylinder, does the steepness of the diffusion gradient decrease with 

 time? 



2. If, in the rubber balloon experiment described in the text, the initial pressure 



of carbon dioxide outside the balloon is 1 atmos. what will be the approxi- 

 mate pressure of the carbon dioxide inside the balloon at equilibrium? 

 outside the balloon? 



3. Two glass containers A and B are connected by a short length of small bore 



glass tubing which is closed with a stopcock. Describe what will happen 

 when the stopcock is opened under the following conditions: (a) A con- 

 tains CO2 at I atmos. pressure and B contains H2 at i atmos. pressure, 

 (b) A contains i volume of CO2; B contains lYz volumes of CO2, but 

 the pressure in A equals that in B because of its higher temperature, (c) A 

 and B each contain CO2 at I atmos. pressure when the stopcock is opened. 

 The temperature in A is then lowered 10° C. (d) A contains one volume 

 of O2 and 2 volumes of CO2; B contains 2 volumes of O2 and one volume 

 of CO2. 



4. How can the CO2 molecules exert a pressure against the inside walls of the 



rubber balloon in the experiment described in the text when rubber is 

 permeable to CO2? 



5. The cation of a mineral salt often accumulates in the vacuole of a plant cell 



in greater concentration than it was present in the external solution. Is it 

 possible to account for such a phenomenon in terms of simple diffusion? 



6. If a porous clay cup arranged as in Fig. 17 is surrounded with a bottle 



containing pure CO2 the water in the glass tube will rise. If the cylinder 

 is first dipped in water and then surrounded by a bottle containing CO2, 

 gas will slowly bubble out of the lower end of the vertical tube. Explain. 



Suggested for Collateral Reading 



Mellor, J. W. Modern inorganic chemistry. Longmans, Green and Co. 

 London. 1925. 



