SI units chemistry

12 Key excerpts on "SI units chemistry"

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  eBook - PDF

  Fundamentals of Physics, Extended

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  Certain physical quantities have been chosen as base quantities (such as length, time, and mass); each has been defined in terms of a standard and given a unit of measure (such as meter, second, and kilogram). Other physical quantities are defined in terms of the base quantities and their standards and units. SI Units The unit system emphasized in this book is the International System of Units (SI). The three physical quanti- ties displayed in Table 1.1.1 are used in the early chapters. Stan- dards, which must be both accessible and invariable, have been established for these base quantities by international agree- ment. These standards are used in all physical measurement, for both the base quantities and the quantities derived from them. Scientific notation and the prefixes of Table 1.1.2 are used to simplify measurement notation. Changing Units Conversion of units may be performed by using chain-link conversions in which the original data are Review & Summary multiplied successively by conversion factors written as unity and the units are manipulated like algebraic quantities until only the desired units remain. Length The meter is defined as the distance traveled by light during a precisely specified time interval. Time The second is defined in terms of the oscillations of light emitted by an atomic (cesium-133) source. Accurate time sig- nals are sent worldwide by radio signals keyed to atomic clocks in standardizing laboratories. Mass The kilogram is defined in terms of a platinum– iridium standard mass kept near Paris. For measurements on an atomic scale, the atomic mass unit, defined in terms of the atom carbon-12, is usually used. Density The density ρ of a material is the mass per unit volume: ρ = m __ V . (1.3.2) figures) should be entered in (a) the cahiz column, (b) the fanega column, (c) the cuartilla column, and (d) the almude column, starting with the top blank? Express 7.00 almudes in (e) medios, (f) cahizes, and (g) cubic centimeters (cm 3 ).

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  eBook - ePub

  Understanding General Chemistry

  • Atef Korchef(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  2 Measurements

  DOI: 10.1201/9781003257059-2

  2.1 Objectives

  At the end of the present chapter, the student should be able to:

  1. Select the appropriate units in the International System of Units (known by the international abbreviation SI) of measurement.
  2. Differentiate between fundamental quantity and derived quantity.
  3. Convert units.
  4. Define and use the basic methods and tools of measurements, such as significant figures and rounding off.

  2.2 Measurements

  Measurement is the process of comparing an unknown quantity with another known quantity of the same kind to find out how many times the first includes the second.

  • Physical quantities are either fundamental (basic) quantities or derived quantities.
  • Fundamental quantities cannot be defined in terms of other physical quantities.Examples: length, time, mass, temperature and amount of a substance.

  Quantity consists of a number telling us how much, and a unit which shows what the scale of measurement is. Examples of base units in SI are given in Table 2.1 . SI base units of mass, temperature and amount of a substance (kg, K and mol, respectively) are widely used by chemists (Table 2.1 ).

  TABLE 2.1 Examples of SI base units

  Base quantity	SI base unit
  Name	Symbol	Name	Symbol
  Length	l, x, r, etc	meter	m
  Mass	m	kilogram	kg
  Time	t	second	s
  Temperature	T	Kelvin	K
  Amount of a substance	n	mole	mol

  Note that:

  • The SI unit of mass is kg (with small or lowercase k), not Kg (with capital K).
  • The SI unit of the amount of a substance (mole) is denoted by mol (without an “e”), not mole. Also, kg is not the SI base unit for the amount of a substance but the SI unit of mass.

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  Engineering Technology NQF2 SB

  TVET FIRST

  • Jowaheer Consulting and Technologies Business Programme Developments(Author)
  • 2013(Publication Date)
  • Macmillan

    (Publisher)

  174 Module 5: SI units of measurement Module 5 SI units of measurement In Topics 3 and 4, you looked at different tools or instruments for measuring certain values, including thermometers, speedometers, scales and voltmeters. In this topic, you are going to study more closely the International System of Units, the most widely used system of measurement in use today. Why and how do we measure things? We measure things so that we are accurate in what we say and do. As an engineering student, you will need to take measurements and perform calculations. The results will be meaningless unless they are numerically and dimensionally correct and accurate. For example, we can say that the length of the classroom is 10. Ten what? Units of measurement provide a common way of understanding the quantity we are describing. In this module, you will gain an understanding of the SI units used in engineering science. By the end of this module, you will be able to: • identify base units of measurement used in engineering science • define the physical quantities that are measured by the SI units • perform conversions according to relevant digital values • derive new units from the relationships between the SI units (i.e. the quantities they measure). Figure 5.1 International system of units Units in this module Unit 5.1 SI base units of measurement Unit 5.2 Converting SI units Unit 5.3 SI derived units of measurement 175 Module 5: SI units of measurement Unit 5.1 SI base units of measurement By the end of this unit, you will be able to: • identify basic units of measurement used in engineering science • define the physical quantities that are measured by the SI units. Different measurement systems Until 1968, South Africa used the imperial system of measurement. South Africa gradually introduced the metric system of measurement using SI units over a number of years. Finally, in 1973, the use of imperial measurements was prohibited.

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  Chemistry, 5th Edition

  • Allan Blackman, Steven E. Bottle, Siegbert Schmid, Mauro Mocerino, Uta Wille(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  A working knowledge of the units and symbols given in table 2.1 is essential in chemistry. However, as you can see, the precise definitions are complicated, and it is not necessary to memorise them; they are given for interest only. Note that we will meet the Planck constant, the Boltzmann constant and the Avogadro constant, all of which are used in the above definitions, in the chapters on atomic energy levels, chemical reactions and stoichiometry, and chemical thermodynamics, respectively. We are all familiar with the SI units for length, metre (m), mass, kilogram (kg), and time, second (s). The SI unit of temperature, kelvin (K), has absolute zero (-273.15 °C), the coldest possible temperature, as its zero point. Temperature is more commonly measured in degrees Celsius (°C) — a temperature in Celsius may be converted to kelvin by adding 273.15. This means that the freezing point of water, 0 °C, is equal to 273.15 K, while the boiling point of water, 100 °C, is 373.15 K. Note that a temperature difference of 1 kelvin (we do not say 1 degree kelvin) is the same as a temperature difference of 1 degree Celsius. The SI unit of amount of substance, a concept that will be discussed in the chapter on chemical reactions and stoichiometry, is the mole (mol), while the unit of electrical current, the ampere (A), will be discussed when we study electrochemistry in the chapter on oxidation and reduction. The SI unit of luminous intensity (the brightness of the radiation emitted by phosphorescent and fluorescent compounds, for example) is the candela (cd). SI units for any physical quantity can be derived from these seven base units. For example, there is no SI base unit for area, but we know that to calculate the area of, for example, a rectangular room we multiply its length by its width (i.e. its length in one dimension by its length in the other).

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  eBook - ePub

  Chemistry

  With Inorganic Qualitative Analysis

  • Therald Moeller(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Some specialized areas of chemistry, which provide bridges to other major fields of study and endeavor, are geochemistry; microbial and medicinal chemistry; agricultural, fertilizer, soil, and food chemistry; polymer chemistry; cellulose, paper, and textile chemistry; and industrial and environmental chemistry. As we have pointed out, whenever people explore materials, living or nonliving, they eventually become concerned with chemistry.

  Units of measure; problem solving

  1.6 Systems of measurement

  Since 1793, when the metric system was devised by the French National Academy of Sciences to overcome the profusion of units handed down from medieval times, various international bodies have been defining and redefining units of measurement and attempting to gain widespread uniformity in their use. For many years scientists everywhere and people in most European countries have used the metric system, which is a decimal system.

  In 1960, the International Bureau of Weights and Measures adopted the International System of Units, known as SI units (for Système Internationale ). The SI system is a revision and extension of the metric system; it provides basic units for each type of measurement. Scientists and engineers throughout the world in all disciplines are now being urged to use the SI system exclusively; most major countries have adopted it.

  The United States, until 1975, officially stayed with a weights and measures system based upon the English system of inches and feet, ounces and pounds, pints and quarts, and so on. The Metric Conversion Act of 1975 commits this country to a policy of voluntary conversion to the metric system by 1985. The United States Metric Board has the job of coordinating the changeover and educating the public to the use of the new units. Everyone must learn how to buy a liter of milk and what to wear when the temperature is 4°C.

  The kilogram and the liter are standard units in both the original metric system and the new SI system, and scientists have dealt in kilograms and liters for a long time. However, some of the units in the SI system are supposed to replace other units that are still widely used. The SI system is finding acceptance, but because scientists are human and, like everyone else, resistant to changing their ways, it will undoubtedly be a long time before the changeover to the new system is complete.

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  The Reform of the International System of Units (SI)

  Philosophical, Historical and Sociological Issues

  • Nadine de Courtenay, Olivier Darrigol, Oliver Schlaudt(Authors)
  • 2019(Publication Date)
  • Routledge

    (Publisher)

  Today, the SI includes the seven base units, the second, metre, kilogram, ampere, kelvin, mole and candela as well as derived units made up of algebraic combinations of the base units, multiples and submultiples and rules for their use. All this is laid out in a document approved by the CIPM and published by the BIPM under the title of The International System of Units SI. It is generally referred to as the SI Brochure. The Brochure, a document of some 75 pages, is now in its 9th edition (2019), and it gives a complete description of the SI. The full text in French and in English is freely available on the BIPM website, and a brief history of the development of ideas during the nineteenth and early twentieth centuries related to units is given in the Introduction. In brief, while there were many advances in definitions of the seven base units of the SI, neither the idea of the great savants of the eighteenth century nor the precepts of Maxwell could be fully realized until now. This was mainly because there had been no way of defining a unit of mass other than as the mass of a particular artefact. Until the redefinition in 2018, the kilogram was still defined as the mass of the International Prototype of the Kilogram kept at the International Bureau of Weights and Measures at Sèvres. However, this problem has now been solved and a fundamental revision of the SI has taken place. The 26th CGPM in 2018 adopted a CIPM proposal to redefine the SI in terms of a set of seven defining constants of nature each having an exact defined numerical value. Taken together they define the same seven base units of the SI that we had before, but they no longer include any material artefacts

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  Electrical Principles & Practice NQF2 SB

  TVET FIRST

  • Jowaheer Consulting and Technologies(Author)
  • 2013(Publication Date)
  • Macmillan

    (Publisher)

  2 Topic 1 SI units of measurement Module 1 SI units of measurement Overview In this topic, you are going to study more closely the International System of Units, the most widely used system of measurement today. Why and how do we measure things? We measure things so that we are accurate in what we say and do. As an engineering student, you will need to take measurements and perform calculations. The results will be meaningless unless they are numerically and dimensionally correct and accurate. For example, we can say that the length of the classroom is 10. Ten what? Units of measurement provide a common way of understanding the quantity we are describing. In this module, you will gain an understanding of the SI units used in engineering. By the end of this module, you will be able to: • identify base units of measurement used in engineering • define the physical quantities that are measured by the SI units • describe the rules when writing SI units of measurements • convert scientific notation to decimal notation and vice versa (convert answer to 3 decimal digits) • list common prefixes used in engineering • derive new units from the relationships between SI units (i.e. the quantities they measure) Range: speed, velocity, acceleration, force, weight, work, energy, torque, resistance, density, pressure and power • explain the theory and measure plane and solid angles. Figure 1.1 International System of Units Module 1 SI Units of measurement 3 ? ? ? Did you know? Units in this module Unit 1.1 SI base units of measurement Unit 1.2 Converting SI units Unit 1.3 SI derived units of measurement Unit 1.1 SI base units of measurement By the end of this unit, you will be able to: • identify base units of measurement used in engineering • define the physical quantities that are measured by SI units • describe the rules when writing SI units of measurement. Different measurement systems Until 1968, South Africa used the imperial system of measurement.

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  Basic Concepts of Chemistry

  • Leo J. Malone, Theodore O. Dolter(Authors)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  28 CHAPTER 1 Chemistry and Measurements 1-4.1 The Metric System There are several systems of measurements that have been developed throughout time. You may be most familiar with the English system of feet, gallons, and pounds. Most of the world and the sciences, however, use a different system known as the metric system of measurement for length, volume, and mass. The principal metric unit for length is the meter. Volume is the space that a sample of matter occupies and its principal metric unit is the liter. Mass is the quantity of matter that a sample contains. The principal metric unit for mass is the gram. (See Figure 1-4.) Since 1975, there have been plans to convert to the metric system in the United States, but there has been little prog- ress toward this goal. However, most citizens are becoming more familiar with this system, such as purchasing soda in a 2-L plastic bottle or an automobile engine now being reported in liters rather than cubic inches. (See Figure 1-5.) Metric units also form the basis of the SI system, after the French Système International (International System). The fundamental SI units that will concern us are listed in Table 1-1. (There are other SI units for measurements that are not used in this text.) The fundamental units of the SI system have very precisely defined standards based on certain known properties of matter and light. For example, the unit of one meter is defined as the distance light travels in a vacuum in 1/299,792,458 th of a second. (Originally, it was one-millionth of the distance between the North Pole and the equator on a meridian passing through Paris.) Obviously, the current standard is extremely precise, but when we are aiming a spaceship at a planet billions of miles away (e.g., Neptune), we need a great deal of precision in our units.

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  eBook - ePub

  Quantities and Units

  The International System of Units

  • Michael Krystek(Author)
  • 2023(Publication Date)
  • De Gruyter Oldenbourg

    (Publisher)

  17 are invariant under such a conversion, there is no need to include quantities such as the angular measures of the plane angle and the solid angle in the category of basic quantities. For mathematical reasons, this is not even possible, since the unit of all quantities of dimension number is the number one. However, as already stated above, the number one cannot be a base unit in any system of units because of its special property.

  3.2  The international system of units (SI)

  The name Système International d’Unités (International System of Units) with the international abbreviation SI was adopted by the Conférence Générale des Poids et Mesures (CGPM) in 1960. The SI has been revised from time to time thereafter to meet user requirements and advances in science and technology. The latest revision of the SI was adopted by the 26th CGPM (2018) and came in force on 20th of May 2019. It is documented in the 9th edition of the SI brochure 18 [2] .

  The SI is a consistent system of units for all fields of life, including international trade, production, safety, health, environmental protection and the scientific foundations on which all these fields are based. The system of quantities underlying the SI and the associated defining equations are based on the currently accepted description of nature (the so-called laws of nature) and are familiar to all scientists, engineers and technicians.

  The definition of the SI units of the revised SI of 2019 is done by means of seven so-called defining constants, which are only to some extent natural constants and whose numerical values expressed by the existing SI units are now regarded as invariant.19 These seven constants are the basis of the definition of the base units of the revised SI, because if they are seen as a set of base units, then the base units of the SI can be obtained from them simply by performing a base transformation. The defining constants

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  Chemistry

  The Molecular Nature of Matter

  • Neil D. Jespersen, Alison Hyslop(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  3 TABLE 1.3 Some Non-SI Metric Units Commonly Used in Chemistry Measurement Unit Symbol Value in SI Units Length angstrom Å 1 Å = 0.1 nm = 10 −10 m Mass atomic mass unit u (amu) 1 u = 1.66054 × 10 −27 kg (rounded to six digits ) metric ton t 1 t = 10 3 kg Time minute min. 1 min. = 50 s hour h 1 h = 60 min. = 3600 s Temperature degree Celsius °C T K = t °C + 273.15 Volume liter L 1 L = 1000 cm 3 Michael Watson 355 mL 1 liter 454 g 454 g FIGURE 1.15 Metric units are commonplace on consumer products. 3 Originally, these conversions were established by measurement. For example, if a metric ruler is used to measure the length of an inch, it is found that 1 in. equals 2.54 cm. Later, to avoid confusion about the accuracy of such measurements, it was agreed that these relationships would be taken to be exact. For instance, 1 in. is now defined as exactly 2.54 cm. Exact relationships also exist for the other quantities, but for simplicity many have been rounded off. For example, 1 lb = 453.59237 g, exactly. TABLE 1.4 Some Useful Conversions Measurement English Unit English/SI Equality a Length inch 1 in. = 2.54 cm yard 1 yd = 0.9144 m mile 1 mi = 1.609 km Mass pound 1 lb = 453.6 g ounce (mass) 1 oz = 28.35 g Volume gallon 1 gal = 3.785 L quart 1 qt = 946.4 mL ounce (fluid) 1 oz = 29.6 mL a These equalities allow us to convert English to metric or metric to English units. Decimal Multipliers Sometimes the basic units are either too large or too small to be used conveniently. For exam- ple, the meter is inconvenient for expressing the size of very small things such as bacteria. The SI solves this problem by forming larger or smaller units by applying decimal multipliers to the base units. Table 1.5 lists the decimal multipliers and the prefixes used to identify them. These were set by the International Bureau of Weights and Measures in 2019. Those listed in red type are the ones most commonly encountered in chemistry.

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  Mathematics for Biological Scientists

  • Mike Aitken, Bill Broadhurst, Stephen Hladky(Authors)
  • 2009(Publication Date)
  • Garland Science

    (Publisher)

  Table 1.2 .

  Table 1.2 Examples of SI derived units

  derived quantity	derived unit	symbol
  area	square meter	m2
  volume	cubic meter	m3
  speed, velocity	meter per second	ms−1
  acceleration	meter per second squared	m s−2
  mass density	kilogram per cubic meter	kg m−3
  amount of substance concentration	mole per cubic meter	mol m−3
  mass fraction	kilogram per kilogram, which may be represented by the number 1	kg kg−1 = 1
  mole fraction	amount of substance per amount of all substances present	mol mol−1 = 1
  per cent	per cent	%

  Some of these derived quantities are assigned special names, because it is useful to think of these combinations of units together. For instance, force is sufficiently important that it is measured in its own unit, the newton, with symbol N. However, because 1 N is defined as that force which would accelerate a 1 kg mass at 1 m s−2 ,

  1   N = 1   kg   ×   1   m   s − 2 = 1   kg   m   s − 2 ,

  (EQ1.22)

  the symbol N is just a synonym for kg m s−2

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  Physical Chemistry

  Understanding our Chemical World

  • Paul M. S. Monk(Author)
  • 2005(Publication Date)
  • Wiley

    (Publisher)

  In a similar way, the Syst` eme Internationale has ‘defined’ other The SI unit of ‘tempera- ture’ T is the kelvin (K). common physicochemical variables. The SI unit of ‘temperature’ T is the kelvin. We define the kelvin as 1/273.16th part of the thermodynamic temperature difference between absolute zero (see Section 1.4) and the triple point of water, i.e. the temperature at which liquid water is at equilibrium with solid water (ice) and gaseous water (steam) provided that the pressure is 610 Pa. The SI unit of ‘current’ I is the amp` ere (A). An amp` ere was The SI unit of ‘current’ I is the amp` ere (A). first defined as the current flowing when a charge of 1 C (coulomb) passed per second through a perfect (i.e. resistance-free) conductor. The SI definition is more rigorous: ‘the amp` ere is that constant current which, if maintained in two parallel conductors (each of negligible resistance) and placed in vacuo 1 m apart, produces a force between of exactly 2 × 10 −7 N per metre of length’. We will not employ this latter definition. The SI unit of the ‘amount of substance’ n is the mole. Curi- The SI unit of ‘amount of substance’ n is the mole (mol). ously, the SI General Conference on Weights and Measures only decided in 1971 to incorporate the mole into its basic set of funda- mental parameters, thereby filling an embarrassing loophole. The mole is the amount of substance in a system that contains as many elementary entities as does 0.012 kg (12 g) of carbon-12. The amount of substance must be stated in terms of the elementary entities chosen, be they photons, electrons, protons, atoms, ions or molecules. The number of elementary entities in 1 mol is an experimentally determined quan- tity, and is called the ‘Avogadro constant’ L, which has the value 6.022 × 10 23 mol −1 . The Avogadro constant is also (incorrectly) called the ‘Avogadro number’. It is

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