Kilogram, definition

Variations in the Force Due to Gravity. The mass of an object is the quantity of matter ia the object. It is a fundamental quantity that is fixed, and does not change with time, temperature, location, etc. The standard for mass is a platinum—iridium cylinder, called the International Kilogram, maintained at the International Bureau of Weights and Measures, ia Snvres, France. The mass of this cylinder is 1 kg by definition (9). AH national mass standards are traceable to this artifact standard. 

Capacity Definitions In any analysis, the capacity per unit time of dynamic equipment (such as conveyors and bagging machines), as well as the rates at which they ac tuaUy perform, must be defined more precisely and realistically than by a mere statement of kilograms or pounds per hour. Some useful definitions employed by the equipment industi y are the following ... 

Typical units for LDjq values are milligrams or grams of material per kilogram of body weight (mg/kg or g/kg, recall that 1 kg = 2.2 pounds). Never be exposed to an LD50 dose of a hazardous chemical- by definition, there is a 50% chance this will kill you and if you survive you are not going to be in good shape. Pay close attention to the permissible exposure level (PEL) instead. This is a more realistic determination of the maximum safe exposure to a material and is usually based on the known effects of the chemical on humans, rather than laboratory animals. 

The IUPAC definition of pH39 is based upon a 0.05M solution of potassium hydrogenphthalate as the reference value pH standard (RVS). In addition, six further primary standard solutions are also defined which between them cover a range of pH values lying between 3.5 and 10.3 at room temperature, and these are further supplemented by a number of operational standard solutions which extend the pH range covered to 1.5-12.6 at room temperature. The composition of the RVS solution, of three of the primary standard solutions and of two of the operational standard solutions is detailed below, and their pH values at various temperatures are given in Table 15.4. It should be noted that the concentrations are expressed on a molal basis, i.e. moles of solute per kilogram of solution. 

During the course of a polyesterification the volume and the weight of the reaction mixture vary because condensation water is released. In most cases, the progress of the reaction is followed by titration of the acid groups at definite intervals the carboxy group concentration is expressed in equivalents per kilogram. Consequently, several authors tried to find out if the weight decrease due to the elimination of water must be taken into account. 

Like mole fraction but unlike molarity, the molality is independent of temperature. The units of molality are moles of solute per kilogram of solvent (mol-kg 1) these units are often denoted m (for example, a 1 m NiS04(aq) solution) and read molal. Note the emphasis on solvent in the definition. To prepare a l m NiS04(aq) solution, we dissolve 1 mol NiS04 in 1 kg of water (Fig. 8.26). 

For historic reasons a number of different units of measurement have evolved to express quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units—the SI units (Systeme Internationale d Unites)— based on the definition of five basic units metre (m) kilogram (kg) second (s) ampere (A) mole (mol) and candela (cd). 

By definition POV is the number of miliequivalents of active oxygen per kilogram of sample" , or in some cases the number of micrograms of active oxygen in one gram of sample, capable of oxidizing iodide to iodine" °°. Many of the methods described in Section V for determination of hydroperoxide classes or individual compounds can also be applied for determination of POV, as total hydroperoxides. The iodometric determination of hydroperoxides in lipids and proteins has been reviewed . 

As both measurements are made in Australia and the weighing instruments (bathroom and doctor s scales) are calibrated to the mass of the Australian standard kilogram, the traceability chain could have stopped there, along with any comparability. Although the definitions do not mention the SI, and of course for some measurements there are no SI units anyway, the more universal the stated reference is, the more measurements will come... 

From the definitions and examples above, it should be clear that metrological traceability is established by a series of comparisons back to a reference value of a quantity. In the mass example it is easy to picture a number of scientists with ever more sophisticated balances comparing one mass with another down the chain of masses from the international prototype of the kilogram to bathroom scales. This is known as a calibration hierarchy. A mass farther up the chain is used to calibrate the next mass down the chain, which in turn can be used to calibrate another mass, and so on, until the final measurement of the mass is made. 

Becker, P (2003), Tracing the definition of the kilogram to the Avogadro constant using a silicon single crystal. Metrologia, 40 (6), 366-75. 

A comparative cost analysis showed that the classical resolution route (Scheme 8.2) was 12 times cheaper than the discovery route (Scheme 8.1). The classical resolution route was successfully scaled up and used to launch the product and provide the first year s market supply. However, using a final-stage resolution meant that by definition half of the synthetic materials were thrown away. When an E factor analysis [8] was performed on the pregabalin synthesis it was found that 86 kg of waste was being produced for every kilogram of the desired product, and this inspired a search for more efficient chemistries. 

According to the modern convention, measurable quantities are expressed in SI (System Internationale) units and replace the centimetre-gram-second (cgs) system. In this system, the unit of length is a metre (m, the unit of mass is kilogram (kg) and the unit of time is second (s). All the other units are derived from these fundamental units. The unit of thermal energy, calorie, is replaced by joule (1 J = 107 erg) to rationalize the definition of thermal energy. Thus, Planck s constant... 

The basic unit of radioactivity is the curie, Ci. One curie is the amount of radioactive material that emits particles at a rate of 3.7 X 1010 disintegrations per second (dps), or 2.2 X 1012 min-1 (dpm). Amounts that large are seldom used in experimentation, so subdivisions are convenient. The milli-curie (mCi, 2.2 X 109 min-1) and microcurie (yu,Ci, 2.2 X 106 min-1) are standard units for radioactive measurements (see Table 6.2). The radioactivity unit of the meter-kilogram-seconds (MKS) system is the becquerel (Bq). A becquerel, named in honor of Antoine Becquerel, who studied uranium radiation, represents one disintegration per second. The two systems of measurement are related by the definition 1 curie = 3.70 X 1010 becquerels. Since the becquerel is such a small unit, radioactive units are sometimes reported in MBq (mega, 106) or TBq (tera, 1012). Both unit systems are in common use today, and radioisotopes received through commercial sources are labeled in curies and bequerels. 

Wherever possible, a traceability chain of measured values terminates in an SI unit. When the base unit for mass is appropriate, this relationship is readily achieved through a mass standard, calibrated in terms of the kilogram prototype. The concept of traceability to SI has to be more carefully considered when conformity to SI depends on the SI concepts in the definition of the SI unit itself. 

In the future, it will end in the value of the Avogadro constant and the value 1 of the atomic mass unit u defined as the mass of 1/12th of the mass of the 12C atom. This will happen when the definition of the kg (now the mass of the prototype of the kilogram ) will have changed into the mass of a number of12C atoms, i.e. of the mass of NAj-m(12C). 1000/12) . 

The preceding sections have used standard molar concentration units for RNA and ions, indicated by brackets or the abbreviation M. Thermodynamic definitions of interaction coefficients are made in terms of molal units, abbreviated m, the moles of solute per kilogram of solvent water. Molal units have the convenient properties that the concentration of water is a constant 55.5 m regardless of the amount ofsolute(s) present, and the molality of one solute is unaffected by addition of a second solute. For dilute solutions, M and m units are interchangeable. We use molal units for the thermodynamic derivations in this section, and indicate later (Section 3.1) the salt concentrations where a correction for molar-molal conversion is required. 

But we can also answer this question by converting molarity to molality. So, what is the molal concentration of a 0.28 molar solution of glucose To convert between molality and molarity, we need to know the density of the solution. The density of a D5W solution is 1.0157 g/mL. We also need to be very careful about the definitions of molarity and molality, and keep in mind whether we are dealing with liters of solutions or kilograms of solvent. 

The most important modem system of units is the SI system, which is based around seven primary units time (second, abbreviated s), length (meter, m), temperature (Kelvin, K), mass (kilogram, kg), amount of substance (mole, mol), current (Amperes, A) and luminous intensity (candela, cd). The candela is mainly important for characterizing radiation sources such as light bulbs. Physical artifacts such as the platinum-iridium bar mentioned above no longer define most of the primary units. Instead, most of the definitions rely on fundamental physical properties, which are more readily reproduced. For example, the second is defined in terms of the frequency of microwave radiation that causes atoms of the isotope cesium-133 to absorb energy. This frequency is defined to be 9,192,631,770 cycles per second (Hertz) —in other words, an instrument which counts 9,192,631,770 cycles of this wave will have measured exactly one second. Commercially available cesium clocks use this principle, and are accurate to a few parts in 1014. 

Exposure" refers to material ingested, inhaled, injected, or simply found in the environment it is expressed in appropriate units, such as milligrams per kilogram (mg/kg) or parts per million (ppm). "Dose" refers to the amount of material reaching the target it is measured in such units as adducts per nucleotide. Because, by this definition, dose can hardly ever be measured, we use "dose" as a synonym for "exposure" when the meaning is clear from the context. 

Salinity was first rigorously defined by Knudsen (1902, p. 28) as the weight in grams of the dissolved inorganic matter in one kilogram of seawater after all bromide and iodide have been replaced by the equivalent amount of chloride and all carbonate converted to oxide. In 1978, the JPOTS decided that a new definition was needed for salinity that was based more on a salinity/conductivity ratio and was termed the practical salinity scale. 

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