Mole (unit) - The Mole As A Unit

The Mole As A Unit

Since its adoption into the International System of Units, there have been a number of criticisms of the concept of the mole as a unit like the metre or the second:

  • the number of molecules, etc. in a given lump of material is a fixed dimensionless quantity that can be expressed simply as a number, so does not require its own base unit;
  • the SI thermodynamic mole is irrelevant to analytical chemistry and could cause avoidable costs to advanced economies;
  • the mole is not a true metric (i.e. measuring) unit, rather it is a parametric unit and amount of substance is a parametric base quantity;
  • the SI defines numbers of entities as quantities of dimension one, and thus ignores the ontological distinction between entities and units of continuous quantities.

In chemistry, it has been known since Proust's law of definite proportions (1794) that knowledge of the mass of each of the components in a chemical system is not sufficient to define the system. Amount of substance can be described as mass divided by Proust's "definite proportions", and contains information that is missing from the measurement of mass alone. As demonstrated by Dalton's law of partial pressures (1803), a measurement of mass is not even necessary to measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, the most notable one being the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties.

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Famous quotes containing the words mole and/or unit:

    “On her left breast
    A mole cinque-spotted, like the crimson drops
    I’ th’ bottom of a cowslip.”
    —William Shakespeare (1564–1616)

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    —George Bernard Shaw (1856–1950)