Grams of atoms

Chemistry imposes a stricter constraint than simply conservation of mass Individual atoms must also be preserved. Let K =, 2,.. ., / be the atomic species present in any one of the components in the system. Let puc be the grams of atom K per gram of species / the matrix p,fc will be compactly indicated as p. Conservation of atoms can be expressed as... 

T) show the relationship between atomic mass units and grams, let us calculate the mass, in amu, of 1.000 gram of atoms. 

Nuclear binding energies may be expressed in many different units, including kilo-joules/mole of atoms, kilojoules/gram of atoms, and megaelectron volts/nucleon. Some useful equivalences are... 

This method follows the ASTM D 1159 and D 2710 procedures and the AFNOR M 07-017 standard. It exploits the capacity of the double olefinic bond to attach two bromine atoms by the addition reaction. Expressed as grams of fixed bromine per hundred grams of sample, the bromine number, BrN, enables the calculation of olefinic hydrocarbons to be made if the average molecular weight of a sufficiently narrow cut is known. 

M HNO3. The concentration of Cu and Zn in the diluted supernatant is determined by atomic absorption spectroscopy using an air-acetylene flame and external standards. Copper is analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc is analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction is used for zinc. Results are reported as micrograms of Cu or Zn per gram of FFDT. 

Faraday s Law of electrolysis states that the amount of chemical change, ie, amount dissolved or deposited, produced by an electric current is proportional to the quantity of electricity passed, as measured in coulombs and that the amounts of different materials deposited or dissolved by the same quantity of electricity are proportional to their gram-equivalent weights (GEW) defined as the atomic weight divided by the valence. The weight in grams of material deposited, IF, is given by... 

The solid metals all have the fee structure, like their predecessors in the periodic table, Ni, Pd and Pt, and they continue the trend of diminishing mp and bp. They are soft, and extremely malleable and ductile, gold more so than any other metal. One gram of gold can be beaten out into a sheet of 1.0m only 230 atoms thick (i.e. 1 cm to 18 m ) likewise Ig Au can be drawn into 165 m of wire of diameter 20/um. The electrical and thermal conductances of the... 

Although the Curies noted that one equivalent gram of radium released one hundred calorics of heat per hour, they were uninterested in the practical implications of this, as they were both devoted to pure scientific discovery. During their work with pitchblende in 1898, the Curies discovered two new radioactive elements, which they named polonium (in honor of Marie s homeland) and radium. By 1902 they had isolated a pure radium salt and made the first atomic weight determination. 

Avogadro s number represents the number of atoms (or molecules) present in one gram-atom (or gram-mole) of any elementary substance (or compound). It has a value of 6.02205 X 1023 [g3]... 

One molecule (or mole) of propane reacts with five molecules (or moles) of oxygen to produce three molecules (or moles) or carbon dioxide and four molecules (or moles) of water. These numbers are called stoichiometric coefficients (v.) of the reaction and are shown below each reactant and product in the equation. In a stoichiometrically balanced equation, the total number of atoms of each constituent element in the reactants must be the same as that in the products. Thus, there are three atoms of C, eight atoms of H, and ten atoms of O on either side of the equation. This indicates that the compositions expressed in gram-atoms of elements remain unaltered during a chemical reaction. This is a consequence of the principle of conservation of mass applied to an isolated reactive system. It is also true that the combined mass of reactants is always equal to the combined mass of products in a chemical reaction, but the same is not generally valid for the total number of moles. To achieve equality on a molar basis, the sum of the stoichiometric coefficients for the reactants must equal the sum of v. for the products. Definitions of certain terms bearing relevance to reactive systems will follow next. 

For most purposes in chemistry, it is sufficient to know the relative masses of different atoms. Sometimes, however, it is necessary to go one step further and calculate the mass in grams of individual atoms. Let us consider how this can be done. 

This reasoning is readily extended to other elements. A sample of any element with a mass in grams equal to its atomic mass contains the same number of atoms, NA, regardless of the identity of the element. 

The importance of Avogadro s number in chemistry should be clear. It represents the number of atoms of an dement in a sample whose mass in grams is numerically equal to die atomic mass of the dement. Thus there are... 

Strategy Nuclear decays are first-order reactions. Use the first-order rate calculation to find k. Part (b) differs from part (c) in that (b) relates concentration and time, while (c) relates concentration and rate. For nuclear decay, concentration can be expressed in moles, grams, or number of atoms. 

The carbon-14 formed by this nuclear reaction is eventually incorporated into the carbon dioxide of the air. A steady-state concentration, amounting to about one atom of carbon-14 for every 1012 atoms of carbon-12, is established in atmospheric C02. More specifically, the concentration of C-14 is such that a sample containing one gram of carbon has an activity of 15.3 atoms/min. A living plant, taking in carbon dioxide, has this same activity, as do planteating animals or human beings. 

A tiny piece of paper taken from the Dead Sea Scrolls, believed to date back to the first century a.d., was found to have an activity per gram of carbon of 12.1 atoms/min. Taking A0 to be 15.3 atoms/min, estimate the age of the scrolls. 

How many moles of iron atoms are present in 1.73 grams of iron ... 

On the other hand, this same amount of electricity will deposit exactly twice as much mercury, 2 x (6.03) = 12.1 grams, from a solution of mercurous perchlorate, Hg2(ClCh)2. If we restate Faraday s experimental finding in terms of the atomic theory, we see that the number of atoms of mercury deposited by a certain quantity of electricity is a constant or a simple multiple of this constant. Apparently this certain quantity of electricity can count atoms. A simple interpretation is that there are packages of electricity. During electrolysis, these packages are parcelled out, one to an atom, or two to an atom, or three. 

---