Recommendation 1 of the 15th CCQM (2009)

On the possible redefinition of the mole and the kilogram

The Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM),

considering

• its previous recommendation to the CIPM on the possible redefinition of the mole and the kilogram, CCQM1 (2007)
• that the present definition of the mole refers to the kilogram,
• the importance of both the kilogram and the mole to the chemical measurement community,

noting

• the progress with experimental efforts to resolve the discrepancy of about 1 part in 10⁶ between the value of the Planck constant arising from the watt balance and the X-ray crystal density/molar mass measurements,
• the development of independent mass spectrometric methods for the determination of the isotope amount ratios of silicon both at natural and enriched isotopic abundances as part of the IAC programme,
• that the level of awareness of the proposal to redefine the mole is low in the relevant communities,
• that support for the proposal to redefine the mole is not yet unanimous,

recommends that

• any decision on redefining the mole and kilogram be deferred until:
  • the discrepancy between results from the watt balance and the X-ray crystal density/molar mass measurements has been resolved; and
  • agreement is demonstrated between values for the Avogadro constant derived from independent measurements of the isotope amount ratios of silicon on samples at both natural and enriched isotopic composition,
• full consideration be given to the interests of the chemical measurement community,
• the BIPM, the National Metrology Institutes, and the other official representatives in the Consultative Committees increase their efforts to spread awareness of the proposals to the various scientific, industrial, and professional organizations, and seek their views at an early stage

states its preference for a redefinition of the mole, the SI unit of amount of substance, based on a fixed value of the Avogadro constant.

DOI : 10.59161/CCQM2009REC1E