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In recent years, the definition of mole, the unit of the amount of substance, has changed to have the base units of the International System defined by "explicit-constant" formulations. The old definition, by referring explicitly to both mass and elementary units, suggests that the mole is a bridge between the macroscopic and microscopic registers. Conversely, the new definition emphasizes the aspect of counting, referred to any kind of elementary unit. Paradoxically, this results in the disappearance of the notion of substance from the very unit of the quantity amount of substance. This change of definition elicited both positive and negative remarks from various authors, in relation to its epistemological, disciplinary, lexical and educational implications. In the present paper, we analyze some of these issues, highlighting the (conflicting) motivations of metrologists and chemists. We argue that the new definition of mole reflects a view of chemistry according to which the microscopic perspective prevails, possibly entailing the loss of reference to the macroscopic register; this could be related with the profound change undergone by the cognitive practices of chemistry along this last century. [ABSTRACT FROM AUTHOR]

In upper-secondary chemistry education, the concept of 'Amount of Substance' occupies a central position within the computation framework. However, comprehending this concept often poses a challenge for students. To address this issue, our study aimed to design and implement a computation skills test to assess the varying levels of students' computation skills in understanding Amount of Substance. The test was administered to a total of 214 first-year students at the secondary schools. To analyse the test scores and unveil students' comprehensive and mastery levels of computation skills, the SOLO Taxonomy was employed for scoring the levels. Additionally, interviews were conducted to identify the underlying reasons for their learning difficulties. Findings revealed that the majority of students demonstrated proficiency in solving relatively straightforward problems and applying basic formulas. Only a small fraction of students reached the advanced relational level, showcasing their ability to apply chemical concepts and methodologies to solve complex problems. Moreover, students exhibited varying degrees of proficiency when dealing with different types of knowledge and problems associated with computations involving solutions and the quantification of microscopic particles. Interviews uncovered students' major learning difficulties. These findings inform the teachers' teaching of Amount of Substance in chemistry education. [ABSTRACT FROM AUTHOR]

The ideas that people build about the levels of interpretation of the matter deserve special attention, since in the scientific literature and in the media reference is made to terms that are used more frequently in the field of Science, among which are the types of substances, measurement systems, physical magnitudes and their units. In this sense, the evolution of these concepts allows us to understand historical and epistemological aspects that made it possible to consolidate academic communities around the construction of chemical knowledge. The aim of the following article is to analyze the concepts quantity of substance and mole, which are evidenced by Chemistry preservice teachers, highlighting the indistinct use of the levels of interpretation of the matter and the need for a formative proposal whose core is the historic and didactic treatment of socio-scientific questions and socio-scientific dilemmas. [ABSTRACT FROM AUTHOR]

The most challenging problems in the field of chemico- and bioanalytical measurements are described. These problems are being solved, in particular, by participating in new international comparisons organized by the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology of the International Committee of Weights and Measures (CCQM CIPM). Solutions of these challenging problems are presented. The objectives and tasks of developing key comparisons in the following areas are described: isotopic measurements; determination of the purity of substances; organic analysis; bioanalytical measurements; measurements of aerosol particle parameters; measurements in the field of gas analysis and electrochemistry. It is shown that participation in international key comparisons allows obtaining valid and reliable results of measurements of the composition and properties of gas and liquid media, as well as solid substances and materials. [ABSTRACT FROM AUTHOR]

This note proposes that the theories of field evaporation and field desorption, as used in atom-probe microscopy and related atomic-level contexts, should be consistently formulated in terms of a set of "seven-dimensional (7-D)" formulae and equations that involve the physical quantity "amount of substance", but make use of an atomic-level constant effectively equal to "one atom" (or, more generally, "one entity"). It is argued that the term "count" should be introduced as an alternative name (more suited to atomic-level contexts) for the quantity "amount of substance". For field evaporation/desorption theories, relevant definitions and formulae are proposed, and compared with the "six-dimensional" system (based on the dimensionless quantity "number of atoms/entities") sometimes used in the literature. Advantages of using a 7-D system are noted. It is argued that there is also an increasing need for a comprehensive system of official nomenclature for atomic-level constants and units, for all three of the extensive quantities "mass", "electric charge" and "amount of substance". It is also argued that, in the longer term, considerations of the kind being proposed here for field evaporation/desorption theories might usefully be applied more generally in atomic-level rate theory. [ABSTRACT FROM AUTHOR]

Im November 2018 trat die Generalkonferenz für Maß und Gewicht (General Conference on Weights and Measures, CGPM), die höchste Instanz der Meterkonvention, zu ihrem 26. Treffen zusammen, um die Revision des Internationalen Einheitensystems (SI) zu beschließen. Die SI-Basiseinheit der Stoffmenge n, das Mol, wird nun über die Avogadro-Konstante N A = 6.022 140 76 × 10 23 mol {N_{\mathrm{A}}}=6.022\hspace{0.1667em}140\hspace{0.1667em}76\times {10^{23}}\hspace{0.1667em}\text{mol} definiert. Der Wert von N A {N_{\mathrm{A}}} wurde ohne Messunsicherheit festgelegt. Diese Revision trat am 20. Mai 2019 in Kraft. Bislang war das Mol über die Masse von 12 g des 12C-Isotops definiert und daher mit einer weiteren SI-Einheit, dem Kilogramm, verknüpft. Dieser Artikel beschreibt die Hintergründe, die Vorteile, die Motivation, die Realisierung (Mise en Pratique) und Weitergabe des Mol sowie die Änderungen nach der Revision. Die derzeit beste Methode der Realisierung und Weitergabe, die X-ray-crystal density (XRCD) Methode (Zählen der Si-Atome in einer Kugel aus hinsichtlich 28Si angereichertem Silicium) wird kurz beschrieben. Dabei wird besonderes Augenmerk auf die Bestimmung der molaren Masse dieses Materials gelegt, die wohl die Größe mit der kleinsten Messunsicherheit in der Chemie darstellt. Die durch die Revision verursachten Änderungen für den Alltag des Chemikers werden mit Beispielen verdeutlicht, um ein besseres Verständnis in Lehre und industrieller Praxis zu vermitteln. During the 26th meeting of the General Conference on Weights and Measures (CGPM) – the highest institution of the Metre Convention – in November 2018, the revision of the International System of Units (SI) has been agreed upon. The base unit of the amount of substance n – the mole – is now defined via the Avogadro constant N A = 6.022 140 76 × 10 23 mol − 1 {N_{\mathrm{A}}}=6.022\hspace{0.1667em}140\hspace{0.1667em}76\times {10^{23}}\hspace{0.1667em}{\text{mol}^{-1}}. N A {N_{\mathrm{A}}} was fixed without any associated uncertainty. The revision has entered into force as from May 20th 2019. Until then, the mole was defined via the mass of 0.012 kg of the 12C isotope and thus linked with another SI unit – the kilogram. This article emphasizes the background, motivation, advantages and methods of the realization (Mise en Pratique) and dissemination of the mole and the changes after the revision. The state-of-the-art method of realization and dissemination using the X-ray-crystal density (XRCD) method (counting the atoms in a silicon sphere enriched in 28Si) is briefly described with special focus on the molar mass determination of this material accompanied by the lowest uncertainty of a chemical quantity so far. The changes and applications of the revision of the mole in the daily practise of a chemist is illustrated by concrete examples from the laboratory aiming at a most clear, simple, but comprehensive explanation important for teaching in schools, universities, and scientific organisations. [ABSTRACT FROM AUTHOR]

Analysis revealed, that in the area of chemical composition measurements high-purity substances may be regarded as the best measurement capabilities in the database of the International Bureau of Weights and Measures. Until now none of the countries of the world has the complete collection of high purity substances with evaluated purity level. At the present time the development of high-purity substances with evaluated values of mass fractions of the base substance is intensively going on to ensure metrological traceability to SI units using both primary methods and other instrumental methods of analysis.

The 2019 revision of the International System of Units (SI), including the redefinition of the mole, and the progress of analytical chemistry technologies allowing single-molecule resolution has brought into sharp focus the dilemma between expressing measurements of ultra-low quantities of elementary entities in terms of amount of substance or in terms of counting quantities. We should prefer the use of amount of substance for these measurements for a number of reasons including to allow intensive and extensive quantities in chemistry to be distinguished and to separate these measurements from those involving the counting of non-elementary entities. The discussion article highlights how a new, non-decimal approach to unit prefixes might in future enable amount of substance to be used usefully down to its natural limit—a single elementary entity. A new prefix symbol 'σ' is proposed to represent the multiplier 1/{NA}. [ABSTRACT FROM AUTHOR]

The base quantity 'amount of substance' is poorly understood and the name and symbol usually avoided. This is because of its formal interpretation as the number of entities multiplied by the reciprocal of the mysterious Avogadro constant, N . If X signifies the kind of entities involved, the number of entities in a sample, N(X), is easily comprehended, and if m (X) is the sample-average entity mass, the total mass, m(X) = N(X) m (X)-an aggregate of N(X) average entity masses-is also conceptually straightforward. However, the corresponding amount of substance, n(X) = N(X)(1/ N )-an aggregate of N(X) 'reciprocal Avogadro constants'-is incomprehensible unless some physical meaning can be attached to 1/ N . By contrast, the base unit, mole, is thought of by chemists as an aggregate of a particular number of entities: mol = $$ {\mathcal N}_{\rm{Avo}} $$ ent, where $$ {\mathcal N}_{\rm{Avo}} $$ is the Avogadro number (equal to g/Da) and ent represents one entity. It makes sense, therefore, to interpret amount of substance as an aggregate of a general number of entities: n(X) = N(X) ent-an easily grasped concept. A 'reciprocal Avogadro constant' is thus seen to actually be exactly one entity. One mole then corresponds to setting N(X) = $$ {\mathcal N}_{\rm{Avo}} $$ , for which the total mass is the relative entity mass in grams-conforming to the original mole concept. [ABSTRACT FROM AUTHOR]

The amount of substance and its unit the mole is a basic concept in chemistry. However, previous research has shown that teaching and learning the concept are challenging tasks for both teachers and students. The purpose of this study was to pinpoint the problems which emerge in the teaching and learning process, and provide integrated suggestions for classroom instruction. By means of videotaping and interviews, the case studies explored how the mole is presented and conceptualized in two secondary classrooms in two different countries, Australia and Taiwan. Data analysis was based on a concept map and focused on how two key ideas were presented in the lessons and perceived by the students: (1) the definition of the mole, and (2) the concept of molar mass. The findings show that during the lessons on the mole, most of the time was spent on solving stoichiometric problems. Conceptually, the number aspect of the mole, that is, Avogadro's number, was emphasized; the concept of molar mass was introduced without meaningfully connecting it to the concept of relative atomic/molecular mass. Although the students were able to solve relevant problems, they could not coherently explain the relations among the concepts. Two critical components for a conceptual understanding of the mole emerged: (1) the number aspect of the mole needs to be justified by its mass aspect, and (2) the connection between molar mass and relative atomic/molecular mass needs to be explicitly explained. The two components provide one explanation for students' algorithmic learning and their confusion in learning about the mole, and serve as concrete suggestions for improving classroom instruction. The study once again manifested the significance of teaching for conceptual understanding in science education. It also exemplifies how a concept map of a specific scientific concept can also be a useful analytical tool in educational research. © 2015 Wiley Periodicals, Inc. J Res Sci Teach 53: 181-214, 2016. [ABSTRACT FROM AUTHOR]

Recent results of measurements of the Avogadro constant by the method of crystal silicon spheres in connection with the planned transition to a new definition of the basic SI unit, the mole, are discussed. [ABSTRACT FROM AUTHOR]

Just as the gram is an Avogadro number of daltons, g = (g/Da) Da, the current definition of the mole can be interpreted as an Avogadro number of entities, as it is often thought of by chemists-and it should be explicitly redefined this way. By introducing a hitherto missing atomic-scale unit for the amount of any substance, the entity (symbol ent), analogous to the dalton for mass, we can then define the mole as: mol = (g/Da) ent-i.e., an Avogadro number of entities. It is argued that the name for the base quantity should be 'chemical amount,' by analogy with 'electric current.' Recent proposals and counterproposals for redefining the mole (and renaming 'amount of substance') are critically discussed in light of the above intuitively obvious definition. [ABSTRACT FROM AUTHOR]

The unit mole is very familiar amongst both chemists and physicists, but the name of the corresponding quantity 'amount of substance' is not so familiar and the concept is still a source of difficulty for many students. This paper reviews and clarifies these concepts and also discusses the definition of the unit mole, and its possible revision.

The mole is a difficult concept. Surveys have shown that even many teachers do not have a proper understanding of it. To help to meet this problem, the SI/IUPAC formulation of the mole is carefully presented and explained. New SI proposals are also briefly discussed. [ABSTRACT FROM AUTHOR]

Most base units in the SI relate to specific sensoric qualities our body is able to observe: space, heat, brightness, etc. The base unit 'mole' incorporates intellectual insight: the atomistic perception of the world. This perception is a quintessence of over 300 years of scientific research. The quintessence, from Dalton's 'The sceptical chymist' to Perrin's Nobel Prize in 1926 and Pauling's 'Nature of the Chemical Bond' in 1939, results in the conclusion that the base unit of the SI quantity 'amount of substance' is not the mole but the dimensionless entity. [ABSTRACT FROM AUTHOR]

'Amount of substance' was introduced in the end of the 1950s as the physical quantity whose unit of measurement is the mole. Fundamental problems associated with this physical quantity have caused a never-ending discussion that continues to this day. One of the reasons for this is the fact that the expression 'amount of substance' is not a good choice, due to its generality and inclusion of the word 'substance'. Considering that samples of matter commonly handled by chemists are extremely numerous in entities and that the quality of being numerous or many is referred to as numerosity (a concept related to numerical cognition), this concept is reproposed as a replacement for amount of substance. Then, taking into account ongoing discussions toward a redefinition of the mole, the following definition is proposed for this SI base unit: 'the mole is the numerosity of a sample of entities numbering exactly 6.022 141 794 × 10'. The relationships between four extensive properties of matter (mass, volume, numerosity and number of entities) are detailed and the resulting intensive physical quantities (proportionality constants) are discussed. The concept numerosity is not the product of an invented synonym; furthermore, as a consequence of its generality, it can be used to express the quantity of entities in samples of matter, as well as of light, chemical reactions, etc. The acceptance that mole is the SI unit of numerosity might also solve most of the pedagogic problems associated heretofore with teaching of mole and amount of substance. [ABSTRACT FROM AUTHOR]

This discussion puts a case of advocatus diaboli: that the Treaty of the Metre, its associated administrative apparatus and the International System of measurement units (SI) has basically failed for chemical measurement and is largely irrelevant to modern analysis, much of practical measurement in modern economies and much of recent technology. The practical use of the chemical unit termed the mole, the introduction to the SI units of the thermodynamic mole and the invention of a new physical quantity called “amount of substance” are each reviewed with the conclusion that the current means of expressing the results of chemical measurements are unsatisfactory in both practice and theory and are imposing large and readily avoidable costs on all advanced economies. [ABSTRACT FROM AUTHOR]

Since the beginning of this millennium, the international metrology community launched ample debates and extremely complex research projects aiming at adopting new definitions for all seven main SI units based on universal physical constants. Taking into account the Resolutions of the General Conference for Weights and Measures, at present, four main SI units - of mass (kilogram), electric current (ampere), thermodynamic temperature (kelvin) and amount of substance (mole), are defined starting from, or derived from artifacts, define state of substances. Aspects regarding the present state of the multidisciplinary researches to support the definitions of kilogram, kelvin and ampere on universal constants (Plank constant, h, Boltzman constant, k and elementary charge, e respectively) have been presented in the previous issues of "Metrologie" revue. This paper continues the approached at topics, focusing on the revue of the theoretic aspects and experiments performed in order to re-define the mole based on Avogadro constant. The main experiments that might assure the mise en pratique of the definition are discussed. Also, main potential advantages and risks of the new definition of the unit of amount of substance are described. [ABSTRACT FROM AUTHOR]

The knowledge of historical facts can help teachers and students to correctly appreciate a variety of scientific theories. It is important to be aware of the evolution of the basic concepts, particularly the ones our students find very abstract and therefore difficult to understand. Historical knowledge of chemical concepts will allow us to understand their difficulties and make them easier to teach successfully. In this paper we answer the following research questions: what was the historic and sociologic context in which chemical equivalent, mole and its magnitude amount of substance were introduced to science? How the lack of historic knowledge in science teaching contributes to the presence of distorted views of science and hampers meaningful learning? [ABSTRACT FROM AUTHOR]

The frequent discussion about which is the magnitude for the unit mole is analyzed. The IUPAC definition of amount of substance as a SI fundamental magnitude is questioned from elementary considerations. The attempt to find a magnitude that reflects a matter property, measured in mole, and not directly related with the number of elementary entities, is presented as vain. The magnitude that represents the number of elementary entities in any material system is accepted to be called Chemical amount, being mole = 6,02214 x 1023 entities their unit. Mole is proposed to be included as suplementary (not fundamental) unit in the SI. [ABSTRACT FROM AUTHOR]

The main element of Metrology is the traceability concept, which has been come applying to the results obtained in the measurement of physical magnitudes for some time. In the chemical measurements the application of the traceability concept has been carried out in a very limited way. Due to this problem, their understanding, their practical application and identification through an uninterrupted chain of comparisons toward the unit of the magnitude of corresponding base (the mol) of the International System (SI) of units, has become a task difficult to carry out. The reference materials (RM) and the certified reference materials (CRM) make possible the transfer of the values of measured magnitudes or assigned between a place and another. They are broadly used for the calibration of measurement instruments, for the evaluation of the analytic methods or of analysis, for the assurance of the long term quality of the measurements, and, in the case of certain biological and technological RM, to facilitate that the properties are expressed in arbitrary units. The CRM supports the establishment from the traceability to the SI of the elementary measurements that carried out the analytical laboratories in any sample type. In this work, key information is provided on the base unit of the magnitude quantity of substance; the interpretation is described given up to now the traceability concept in metrology and its application to RM and the results reached in an environmental laboratory through the application of RM and CRM are shown, which allow to achieve the traceability to the SI. [ABSTRACT FROM AUTHOR]

In this article the role of reference materials is confined to chemical measurements only. Recognized reference materials are one of the tools to obtain comparability of analytical results. Recognition demands confidence in the reference materials and in the reference material producers. A reference material producer is a technical competent body that is fully responsible for the certified or other property values of the reference material. The "analyte" has to be specified in relation to the selectivity of analytical procedure. The full range of reference materials can be presented as a three-dimensional space of the coordinates: analyte, matrix and application. If reference materials are used for calibration or correction of calibrations they establish the traceability of results of chemical measurements. The traceability is only valid within a stated range of uncertainty. Pure substances can represent the unit of amount of substance. A precondition is the microscale specification of the analyte and the accurate determination of the main component and/or the impurities. [ABSTRACT FROM AUTHOR]

This commentary draws on the perspective of teaching and learning to discuss the issue of redefining the mole. [ABSTRACT FROM AUTHOR]

The International System of Units' (SI) base unit of the quantity "amount of substance" is the mole (symbol: mol). After the revision of the SI to be implemented in 2019, when all SI units will be based solely on constants, the mole will be defined through a fixed value of the Avogadro constant NA. One mole contains exactly 6.02214076 × 1023 elementary entities, meaning the mole will no longer be linked to the kilogram. Currently, the mole is defined via the mass of exactly 0.012 kg of the 12C isotope which links it to the kilogram prototype. The history, changes, and implications of the revised definition of the mole are discussed here from the chemist's point of view. The ability to count entities such as atoms or molecules (precisely enough to enable a revision of the SI and preserve consistency of previous and future measurements) is crucial. This is achieved with the realization (Mise en Pratique) based on the X‐ray‐crystal density (XRCD) method (counting the atoms in a silicon sphere). The determination of NA, focusing on the measurement of the molar mass of silicon highly enriched in the 28Si isotope, with the lowest uncertainty so far, is presented. [ABSTRACT FROM AUTHOR]