Question 12

Explain the following laws:

  • Dalton’s
  • Boyles
  • Henry’s
  • Graham’s
  • Fick’s Law of Diffusion

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College Answer

The universal gas laws form the basis of oxygen therapy and delivery, pressure and volumetric 
monitoring as well as a key to understanding the solubility of gases in blood.
All the equations and relationship are straightforward so this question provided a good opportunity to score marks. Unfortunately many candidates were aware of the properties of the ideal gases but not the named laws. This led many candidates to omit major sections of the answer and thus scored no marks. Several candidates wasted time with complicated diagrams as well as equations and descriptions (scoring no additional marks). Many candidates were unable to identify Grahams Law (rate of diffusion inversely proportional to the square root of the molecular weight) but included it in an expanded Fick’s Equation.