scholarly journals A new definition for the mole based on the Avogadro constant: a journey from physics to chemistry

2011 ◽  
Vol 369 (1953) ◽  
pp. 3993-4003 ◽  
Author(s):  
Martin J. T. Milton
Keyword(s):  
Measurement Uncertainty ◽  
Early Development ◽  
International System ◽  
Atomic Masses ◽  
Amount Of Substance ◽  
Avogadro Constant ◽  
System Of Units ◽  
Considerable Debate ◽  
Recent Addition ◽  
Base Units

The mole is the most recent addition to the set of base units that form the International System of Units, although its pre-cursor the ‘gram-molecule’, had been in use by both physicists and chemists for more than 120 years. A proposal has been published recently to establish a new definition for the mole based on a fixed value for the Avogadro constant. This would introduce consistent relative uncertainties for the molar and the atomic masses while making no change to the system of relative atomic masses (‘atomic weights’). Although the proposal would have little impact on the measurement uncertainty of practical work, it has stimulated considerable debate about the mole and the nature of the quantity amount of substance. In this paper, the rationale for the new definition is explained against the background of changes in the way the quantity amount of substance has been used, from its first use during the early development of thermodynamics through to the use of the ‘number of gram-molecules’ at the end of the nineteenth century.

New Avogadro Spheres for the Redefinition of the Kilogram

2014 ◽  
Vol 613 ◽  
pp. 17-25 ◽  
Author(s):  
Arnold Nicolaus ◽  
Rudolf Meeß ◽  
Guido Bartl
Keyword(s):  
Measurement Uncertainty ◽  
International System ◽  
Fundamental Constant ◽  
Machining Process ◽  
Average Roughness ◽  
Weights And Measures ◽  
Avogadro Constant ◽  
System Of Units ◽  
Surface Deviations ◽  
Form Deviation

The General Conference on Weights and Measures (CGPM) discusses the improvements of a possible revision of the International System of Units (SI). For the new definition of the kilogram apart from an artifact of Platinum-Iridium a suitable fundamental constant seems to be found, to which the kg could be related. Although the Planck constant, h, is being considered for the new definition, its value can currently be determined with less uncertainty from the value of the Avogadro constant, NA. As well the determination of the Avogadro constant is suitable as a primary method for the subsequent realization of the kilogram. The international Avogadro group has reached so far a relative measurement uncertainty of 3×10-8, mainly limited by the interferometric measurement of the volume of the 28Si-spheres, used to count the atoms. The dominant influence on the measurement uncertainty is a contribution which subsumes wavefront aberrations due to surface deviations and irregularities of the spheres polished from our partner at CSIRO, Australia. A new multi-step machining process, developed and realized at PTB, reduces considerably the surface contamination and creates spheres with surface properties which exceed the standards in matters of form deviation and surface roughness. The manufacturing process incorporates highly reproducible multi-step grinding and polishing steps. The surfaces are almost free of scratches and show average roughness values below 0.3 nm. The form shows some regular, long wavelength errors below 30 nm in amplitude, collocated conform to crystal orientation.

Redefinition of the mole and uncertainty of analytical measurements

2019 ◽  
Vol 85 (2) ◽  
pp. 5-11
Author(s):  
L. A. Konopel’ko ◽  
R. L. Kadis ◽  
Yu. A. Kustikov
Keyword(s):  
Molar Mass ◽  
International System ◽  
Mass Measurements ◽  
Atomic Masses ◽  
Amount Of Substance ◽  
Small Uncertainty ◽  
System Of Units ◽  
Definition Of ◽  
New Si ◽  
Fundamental Physical

Redefinition of the basic units of the International System of Units (SI) — the kilogram, mole, ampere, and kelvin, — which are now expressed in terms of fundamental physical constants means a substantial revision of the system. In particular, the new definition of the mole fixing the value of the Avogadro constant sets a unit of the amount of substance, which is independent of the unit of mass. We consider some consequences of redefining (the mole and kilogram) and focus on the uncertainty of measuring the amount of substance and related quantities which are important for description of the mixture composition. The issue regarding the molar mass of the substance and associated uncertainty is considered in detail It is noted that calculation of the molar mass using relative atomic masses, involves the molar mass constant which is not equal exactly to 1 g/'mol in the new SI. This introduces an additional, though very small, uncertainty of less than 1 x 10-9in relative terms. The budget of uncertainty for the amount of substance determined through the mass measurements when the mass is measured with the highest accuracy is scrutinized. It is demonstrated that for substances of less than 99.98% purity, the uncertainty associated to the purity is comparable to that of relative atomic masses of the elements. For high-purity substances, the uncertainty in the relative atomic masses have the largest contribution to the budget. Anyhow, the uncertainty associated to the molar mass constant is three orders of magnitude less than the nearest contribution to the uncertainty attributed to weighing. In the case of derived quantities which are the ratio of two quantities of the same kind, the additional uncertainty does not arise at all. This is illustrated by the calculation of the mole fraction of a component in the gravimetrically prepared gas mixture.

scholarly journals On the five base quantities of nature and SI (The International System of Units)

2011 ◽  
Vol 47 (2) ◽  
pp. 241-246
Author(s):  
G. Kaptay
Keyword(s):  
International System ◽  
Fundamental Constant ◽  
Fundamental Constants ◽  
Planck Constant ◽  
Amount Of Substance ◽  
Substance Mole ◽  
System Of Units ◽  
Elementary Charge ◽  
Base Units ◽  
Constants Of Nature

It is shown here that five base quantities (and the corresponding five base units) of nature are sufficient to define all derived quantities (and their units) and to describe all natural phenomena. The base quantities (and their base units) are: length (m), mass (kg), time (s), temperature (K) and electric charge (C). The amount of substance (mole) is not taken as a base quantity of nature and the Avogadro constant is not considered as a fundamental constant of nature, as they are both based on an arbitrary definition (due to the arbitrary value of 0.012 kg for the mass of 1 mole of C-12 isotope). Therefore, the amount of substance (mole) is moved from the list of base quantities to the category of the supplementary units (to be re-created after its abrogation in 1995). Based on its definition, the luminous intensity (cd) is not a base quantity (unit), therefore it is moved to the list of derived quantities (units). The ampere and coulomb are exchanged by places in the list of base and derived units, as ampere is a speed of coulombs (but SI defines meter, not its speed as a base unit). The five base quantities are re-defined in this paper by connecting them to five fundamental constants of nature (the most accurately known frequency of the hydrogen atom, the speed of light, the Planck constant, the Boltzmann constant and the elementary charge) with their numerical values fixed in accordance with their CODATA 2006 values (to be improved by further experiments).

scholarly journals Adapting the International System of Units to the twenty-first century

2011 ◽  
Vol 369 (1953) ◽  
pp. 3907-3924 ◽  
Author(s):  
Ian M. Mills ◽  
Peter J. Mohr ◽  
Terry J. Quinn ◽  
Barry N. Taylor ◽  
Edwin R. Williams
Keyword(s):  
International System ◽  
International Committee ◽  
First Century ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
Magnetic Constant ◽  
Base Units ◽  
New Si

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed.

scholarly journals The kelvin redefinition and its mise en pratique

2016 ◽  
Vol 374 (2064) ◽  
pp. 20150037 ◽  
Author(s):  
B. Fellmuth ◽  
J. Fischer ◽  
G. Machin ◽  
S. Picard ◽  
P. P. M. Steur ◽  
...  
Keyword(s):  
International System ◽  
Thermodynamic Temperature ◽  
Fundamental Constants ◽  
Primary Thermometry ◽  
A Value ◽  
System Of Units ◽  
Mise En Pratique ◽  
Explicit Constant ◽  
Definition Of ◽  
Base Units

In 2018, it is expected that there will be a major revision of the International System of Units (SI) which will result in all of the seven base units being defined by fixing the values of certain atomic or fundamental constants. As part of this revision, the kelvin, unit of thermodynamic temperature, will be redefined by assigning a value to the Boltzmann constant k . This explicit-constant definition will define the kelvin in terms of the SI derived unit of energy, the joule. It is sufficiently wide to encompass any form of thermometry. The planned redefinition has motivated the creation of an extended mise en pratique (‘practical realization’) of the definition of the kelvin ( MeP -K), which describes how the new definition can be put into practice. The MeP -K incorporates both of the defined International Temperature Scales (ITS-90 and PLTS-2000) in current use and approved primary-thermometry methods for determining thermodynamic temperature values. The MeP -K is a guide that provides or makes reference to the information needed to perform measurements of temperature in accord with the SI at the highest level. In this article, the background and the content of the extended second version of the MeP -K are presented.

scholarly journals Definition of the mole (IUPAC Recommendation 2017)

2018 ◽  
Vol 90 (1) ◽  
pp. 175-180 ◽  
Author(s):  
Roberto Marquardt ◽  
Juris Meija ◽  
Zoltán Mester ◽  
Marcy Towns ◽  
Ron Weir ◽  
...  
Keyword(s):  
International System ◽  
International Committee ◽  
Fundamental Physical Constants ◽  
Weights And Measures ◽  
Technical Report ◽  
System Of Units ◽  
Iupac Recommendation ◽  
Definition Of ◽  
Base Units ◽  
Fundamental Physical

AbstractIn 2011 the General Conference on Weights and Measures (CGPM) noted the intention of the International Committee for Weights and Measures (CIPM) to revise the entire International System of Units (SI) by linking all seven base units to seven fundamental physical constants. Of particular interest to chemists, new definitions for the kilogram and the mole have been proposed. A recent IUPAC Technical Report discussed these new definitions in relation to immediate consequences for the chemical community. This IUPAC Recommendation on the preferred definition of the mole follows from this Technical Report. It supports a definition of the mole based on a specified number of elementary entities, in contrast to the present 1971 definition.

RESEARCH ON STABILITY ANALYSIS OF INTERNATIONAL PROTOTYPE KILOGRAM

2013 ◽  
Vol 24 ◽  
pp. 1360004
Author(s):  
XIAOPING REN ◽  
YUE ZHANG ◽  
JIAN WANG ◽  
QINGXIONG REN ◽  
QINGMAO REN
Keyword(s):  
Stability Analysis ◽  
International System ◽  
Calibration Data ◽  
Surface Stability ◽  
Standard Methods ◽  
System Of Units ◽  
Modern Mass ◽  
Base Units ◽  
Adjustment Of Parameters ◽  
Measured Mass

Today, the kilogram is the last of the seven base units of the International System of Units (SI) which is based on a physical artifact. The demands of modern mass metrology have led to an increasing focus on the surface stability and analysis of mass standard. Methods for evaluating the correlation between the measured mass values of the prototypes of the kilogram includes: collection of historical calibration data for kilogram prototypes, setting up a model for deterministic and random changes in the mass of a kilogram prototype (relative to the IPK), adjustment of parameters in a model using historical calibration data, and prediction of future mass values of a kilogram prototype using model and adjusted parameters.

scholarly journals Systematic comparison of post-column isotope dilution using LC-CO-IRMS with qNMR for amino acid purity determination

2019 ◽  
Vol 411 (27) ◽  
pp. 7207-7220
Author(s):  
Philip J. H. Dunn ◽  
Dmitry Malinovsky ◽  
Eli Achtar ◽  
Cailean Clarkson ◽  
Heidi Goenaga-Infante
Keyword(s):  
Measurement Uncertainty ◽  
Isotope Dilution ◽  
International System ◽  
Direct Analysis ◽  
Uncertainty Budget ◽  
Chemical Oxidation ◽  
Resonance Spectroscopy ◽  
Purity Determination ◽  
System Of Units

Abstract Determination of the purity of a substance traceable to the International System of Units (SI) is important for the production of reference materials affording traceability in quantitative measurements. Post-column isotope dilution using liquid chromatography-chemical oxidation-isotope ratio mass spectrometry (ID-LC-CO-IRMS) has previously been suggested as a means to determine the purity of organic compounds; however, the lack of an uncertainty budget has prevented assessment of the utility this approach until now. In this work, the previously published ID-LC-CO-IRMS methods have not only been improved by direct gravimetric determination of the mass flow of 13C-labelled spike but also a comprehensive uncertainty budget has been established. This enabled direct comparison of the well-characterised ID-LC-CO-IRMS method to quantitative nuclear magnetic resonance spectroscopy (qNMR) for purity determination using valine as the model compound. The ID-LC-CO-IRMS and qNMR methods provided results that were in agreement within the associated measurement uncertainty for the purity of a sample of valine of (97.1 ± 4.7)% and (99.64 ± 0.20)%, respectively (expanded uncertainties, k = 2). The magnitude of the measurement uncertainty for ID-LC-CO-IRMS determination of valine purity precludes the use of this method for determination of purity by direct analysis of the main component in the majority of situations; however, a mass balance approach is expected to result in significantly improved measurement uncertainty.

scholarly journals The watt balance: determination of the Planck constant and redefinition of the kilogram

2011 ◽  
Vol 369 (1953) ◽  
pp. 3936-3953 ◽  
Author(s):  
M. Stock
Keyword(s):  
International System ◽  
Accurate Determination ◽  
Electrical Power ◽  
Planck Constant ◽  
System Of Units ◽  
Macroscopic Quantum Effects ◽  
Watt Balance ◽  
Definition Of ◽  
Base Units

Since 1889, the international prototype of the kilogram has served as the definition of the unit of mass in the International System of Units (SI). It is the last material artefact to define a base unit of the SI, and it influences several other base units. This situation is no longer acceptable in a time of ever-increasing measurement precision. It is therefore planned to redefine the unit of mass by fixing the numerical value of the Planck constant. At the same time three other base units, the ampere, the kelvin and the mole, will be redefined. As a first step, the kilogram redefinition requires a highly accurate determination of the Planck constant in the present SI system, with a relative uncertainty of the order of 1 part in 10 8 . The most promising experiment for this purpose, and for the future realization of the kilogram, is the watt balance. It compares mechanical and electrical power and makes use of two macroscopic quantum effects, thus creating a relationship between a macroscopic mass and the Planck constant. In this paper, the operating principle of watt balance experiments is explained and the existing experiments are reviewed. An overview is given of all available experimental determinations of the Planck constant, and it is shown that further investigation is needed before the redefinition of the kilogram can take place. Independent of this requirement, a consensus has been reached on the form that future definitions of the SI base units will take.

scholarly journals Changing the status of mmHg

2019 ◽  
Vol 25 (1) ◽  
pp. 81-82 ◽  
Author(s):  
Dominik Pražák ◽  
Václav Sedlák ◽  
Ekrem Sınır ◽  
František Pluháček
Keyword(s):  
International System ◽  
Medical Doctor ◽  
Public Attention ◽  
International System Of Units ◽  
System Of Units ◽  
The Status ◽  
User Groups ◽  
The Media ◽  
Base Units

AbstractThe new International System of Units (SI) came into force this May, and while the media and public attention are focused on the changes in the base units, there are also other changes introduced. One of them is the abolition of millimetre of mercury (mmHg). This simplifies the SI but also can cause problems to the patients which are extremely conservative user groups (although this unit is still supported by some other authoritative documents). Hence, it is necessary to increase awareness of both the medical doctor and the patients.

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