About 6.02× 10 2 3 atoms is 1 mole, just like people often say that a dozen is 12 atoms, and "mole" is just a special unit quantity like "dozen". 0.0 12kg (1 2g)12c (carbon12) contains1mol.
2018 165438+1October16 the 26th international metrology conference adopted the resolution of "revising the international system of units", which formally updated the definitions of four basic units including the international standard quality unit "kilogram". The new international system of units uses physical constants to redefine the mass unit "kilogram", current unit "ampere", degree-day "Kelvin" and substance quantity unit "mole".
Chinese name: Moore mbth: mole abbreviation: mole, gram atom: symbol of the unit of quantity of matter: Mol definition, basic information, development history, absorption coefficient, chemical equation. When using Mol definition, you should specify basic particles, which can be atoms, molecules, ions, atomic groups, electrons, protons, neutrons and other particles, or a specific combination of these particles. According to international regulations, 1mol particle aggregate contains the same number of particles as 0.0 1 2kg 1 2 C (carbon 12), that is, the number of structural particles contained in any one mole of substance is equal to 0.0 12 kg/kloc-0. Sometimes, the mass of one mole of a substance is called the molar mass of the substance, which is represented by the symbol m, for example, the m of hydrogen H 2 is 2.02× 10-3 kg. For a substance with a mass f of m, the ratio of m to μ is called the amount of the substance (also called the number of moles), =Mμ. For example, M=4.04× 10-3 kg, and the number of moles of hydrogen H 2 =2. The volume Vm occupied by one mole of substance is called molar volume. The molar volume of gas depends on temperature and pressure. In the standard state, the VM of the ideal gas is 22.4438+045438+00L. Fmol-1. The molar volumes of solid and liquid substances have little to do with temperature and pressure. A mole of different solid substances and different liquid substances have different volumes. According to the accurate determination of scientific experiments, it is known that the number of 12c contained in a carbon atom of 0.0 1 2kg (carbon12) is about 6.02× 10 2 3. Why do you use "12g" and "1 2 C (12)" to define moles? The main reasons are as follows (middle school study only): Why do you have to take 12g? Because its nucleus contains equal amounts of neutrons and protons. Why can the equivalent of neutron proton number be used as the reference atom of molar number? Because neutrons have one more negative electron and some radiation than protons, strictly speaking, the mass of a single neutron is slightly higher than that of protons, and its mass is1.649286×10-27 kg (939.5563 MeV). Slightly greater than the mass of protons (the mass of protons is1.672621637 (83) ×10-27 kg). Scientific counting is too complicated. In order to measure the mass of other nuclei by comparison, it is necessary to take an intermediate value of neutron mass and proton mass (averaging is a traditional measurement method). Then 1 2 C (C 12) kernel is the best choice as a reference, and it is generally stable. Therefore, in scientific measurement, one twelfth of the nuclear mass 1 2 C (carbon 1 2) is closest to the mass of neutrons or protons. A certain number (Avogadro constant, or one mole) of neutrons (protons-you can imagine neutron protons as particles with the same mass here) is basically equal to 1 gram, so a mole of X element contains m (natural number) protons and n (natural number) neutrons, that is, m+n grams. And m+n is exactly the atomic weight. M determines the position of the atom in the periodic table of elements, and n determines the atomic weight of the same element atom. 20 18, 165438+ 10, 16 international metrology conference passed a resolution, 1 mol will be defined as "a system accurately contains 6.02214076×/kloc. At the same time, the Avogadro constant is revised to 6.022 14076× 10 23. In basic information science, the aggregate containing 6.02×10 2 3 particles is regarded as a unit, called mole. Is the unit (symbol n) that represents the quantity of a substance, abbreviated as Mo, and the unit symbol is mol. The carbon atom of 1mol contains 6.02× 10 2 3 carbon atoms, and its mass is 12g. The sulfur atom of 1mol contains 6.02× 10 2 3 sulfur atoms, and its mass is 32g. Similarly, the mass of any substance in 1 mol is in grams, which is numerically equal to the relative atomic mass or relative molecular mass of atoms (it is a fixed value). The molecular weight (relative molecular weight) of water is 18, and the mass of 1mol water is 18g, containing 6.02× 10 2 3 water molecules. Generally, the mass of 1mol is called the molar mass of the substance (symbol m), and the unit of molar mass is gram/mol, which is read as "gram per mole" (symbol g/mol). For example, the molar mass of water is 18g/mol, written as m (H2O) = 18g. What is the relationship between mass (M), quantity (N) and molar mass (M)? Namely: n=m/M, m=n×M, M=m/n general formula: n (amount of substance) =n (number of particles) /N A (Avon Gadereau constant) =m (mass) /M (molar mass) =V (gas volume)/Vm (molar volume: STP (standard condition: 273k (0℃)/kloc-0). For example, one mole of water molecules can be written as the development history of 1 molH 2 O or 1 mol water molecules. Moore joined the 197 10 international system of units, and the 14 international metrology conference with 4 1 countries decided to join. The molar sleeve is used to calculate the number of particles, the mass of matter, the volume of gas, the concentration of solution, the change of heat during the reaction and so on. Moore comes from the Latin moles, which means to accumulate a lot. 197 1 The 14th International Metrology Conference defined the mole in the following two paragraphs: "Mole is the amount of substances in a system, and the number of basic units contained in this system is equal to the number of atoms in 0.0 12kg carbon-12." "When using moles, you should specify the basic unit, which can be atoms, molecules, ions, electrons and other particles, or a specific combination of these particles." The last two paragraphs should be regarded as a whole. The number of carbon atoms in 0.0 12kg carbon-12 nuclide is Avogadro's constant (NA), and the approximate value measured in the present experiment is N A =6.02× 10 2 3. Moles are different from ordinary units. It has two characteristics: ① Measuring microscopic basic units, such as molecules and ions, cannot be used to measure macroscopic substances. (2) it takes Avon Gadereau number as the unit of measurement, and it is a batch, not a number, to measure the number of particles such as molecules and atoms. It can also be used to measure the specific combination of microscopic particles, for example, to measure the molar amount of sulfuric acid, that is, 1mol sulfuric acid contains 6.02× 10 2 3 sulfuric acid molecules. Molar is the most widely used unit of measurement in chemistry, such as calculation of chemical reaction equation, calculation in solution, preparation and dilution of solution, calculation of chemical equilibrium, molar volume of gas, thermochemistry and so on. The molar extinction coefficient, molar absorption coefficient and molar absorption coefficient spectrophotometry are based on the selective absorption of electromagnetic radiation by substances with different molecular structures, and belong to molecular absorption spectrum analysis. When light passes through the solution, the molecules of the measured substance absorb monochromatic light with a certain wavelength, and the intensity of the absorbed light is proportional to the distance through which the light passes. Although Bouguer put forward the mathematical expression of the above relationship as early as 1729, it is generally believed that Lambert first discovered the expression in 1760, and its mathematical form is: T=I/I0= 10(-kb), where I0 is the incident light intensity and i is the transmitted light intensity,/. Beer's law is equivalent to Bouguer's law, except that Beer's law is expressed by concentration. Two laws are combined to form Bill-Bouguer's Law: T=I/I0= 10(-kb) where c is the concentration of light-absorbing substance (usually in g/L or mg/L). The logarithm of the above formula is based on 10, and a linear expression is obtained: a =-logt =-log (I/i0) = log (i0/I) = ε BC, where a is absorbance and ε is molar absorption coefficient or extinction coefficient. The above expression is usually called Beer's Law. It shows that when monochromatic light with a specific wavelength passes through the solution, the absorbance of the sample is directly proportional to the concentration of absorbent in the solution and the distance through which the light passes. When the wavelength, solution and temperature are determined, the molar extinction coefficient is determined by the characteristics of a given substance. In fact, the measured molar extinction coefficient is also related to the instrument used. Therefore, in quantitative analysis, the molar extinction coefficient of known substances is usually not used, but one or more substances with known concentrations are used to make calibration or working curves. The mathematical expression of beer's law light absorption coefficient is A=kbc. If the concentration of solution C is in g/L and the optical diameter of solution B is in cm, the constant k is called the light absorption coefficient, which is denoted by A and the unit is L/(g cm) [L/(g cm]]. A = KBC can be written as A=abc. When the KBC formula A = 1 mol/L and B = 1cm, the coefficient K is called molar absorption coefficient, expressed as ε, and the unit is L/(mol cm) [L/(mol cm)], and A=kbc can be written as A = ε C, which can not be used in practical work. ε value is related to the wavelength of incident light and the properties of solution. For example, when NADH is at 260nm, ε is 15000, written as ε 260 NADH =15×103; At 340nm, ε is 6220, and ε340NADH=6.22× 10 3. If in the formula A=kbc, C is the percentage concentration (w/v) and B is cm, then the constant K can be expressed by E%, which is called specific absorption coefficient or percentage absorption coefficient, and A=kbc can be written as A=E%bc. When the chemical structure of the measured object is known, the ε value can be analyzed. If the chemical structure of the measured object is unknown, ε cannot be determined. At this time, it is very convenient to analyze with a specific absorption coefficient. A, ε and E are often used for rough quantitative analysis, mainly for qualitative analysis. Chemical equation A chemical equation can represent the ratio of quantity and mass of substances between reactants and products. For example: 2H 2 +O 2 = (ignition) =2H 2 O coefficient ratio 2: 1: 2 particle number ratio 2: 1: 2 mass ratio 2: 1: 2 mass ratio 4: 32: 36 From the above analysis, it can be seen that the coefficient ratio of each substance in the chemical equation is the amount of substances between them. Using this principle, we can calculate the amount of each substance according to the chemical equation. One twelfth of the mass of carbon atoms (1 2 C) is the international standard of relative atomic mass. It is known that 12g 1 2 C contains 6.0221367×102 3 carbon atoms. This number is called Avon Gadereau number, so it can also be said that the amount of matter containing several Avon Gadereau elementary particles is 1mol. For example, 1mol oxygen molecule contains 6.022 1367× 10 2 3 oxygen molecules, and its mass is 3 1.9988g. 1mol hydrogen ion contains 6.0221367×/kloc.