Gram-formula weight

Heat evolved, in Idlogram-calories per gram formula weight, on solution in water at 18 C. Computed from data in Bichowsky and Rossini, Theimochemishy of Chemical Substances, Reinhold, New York, 1936. 

Moreover, the Relative Size argument also applies to those divalent iodides which are approximately close-packed arrays of iodide (cp. Wyckoff 24)). The following table shows for such compounds the gram-formula weights, the X-ray determined densities, and hence the volume Vanion (cc/gm/atom) occupied by the iodide gram/ion, which has a minimum value of about 28 cc. 

Salt Gram-Formula Weight (GFW) Density q from (X-rays) V anion (GFW/2e) cc/mole... 

For nonmolecular substances like sodium chloride, the use of the word mole, with its connotation of molecules, is inappropriate. A comparable unit, the gram formula weight, is used it is defined as the sum in grams of the atomic weights of all the atoms in the chemical formula of the substance. For sodium chloride (NaCl), one gram formula weight is calculated as... 

One gram formula weight of calcium chloride, CaCl2,... 

The molarity is the number of moles (or gram formula weights) of solute in 1 liter of solution. This unit is the most convenient one for laboratory work. A solution of calcium chloride that is 0.5 molar (abbreviated with an uppercase M as 0.5M) contains one-half mole of CaClj (55.49 grams) in enough water to make the total volume 1 liter. 

The solution, then, is 0.000129 M Ag2C03, which is identical to the value found for the concentration. Because the gram formula weight of Ag2C03 is 275.75, each liter of solution contains... 

In the two previous examples, the sucrose and santonic acid existed in solution as molecules, instead of dissociating to ions. The latter case requires the total molality of all ionic species. Calculate the total ionic molality of a solution of 50.0 grams of aluminum bromide (AlBr3) in 700 grams of water. Because the gram formula weight of AlBt3 is... 

Heat of formation. The heat of formation of a substance, as MX (crystal), is taken to mean the heat evolved in the reaction of forming one mole (gram formula weight) of that substance from its elements in their standard states (as, for example M (liq.) + X2 (g) =MX(c)) at a constant pressure (or a fugacity) of one atmosphere and, unless otherwise... 

If a substance undergoes a transformation from one physical stale to another, such as a polymorphic transition, the fusion or sublimation of a solid, or the vaporization of a liquid, the heat adsorbed hy the substance during the transformation is defined as the latent heat of transformation (transition, fusion, sublimation or vaporization). It is equal in the enthalpy change of the process, which is the difference between the enthalpy of the substance in the two states at (he temperature of the transformation. For the purpose of thcrmochemical calculations, i( is usually reported as a molar quantity with die units of calories (or kilocalories) per mule (or gram formula weight). The symbol L or AH. with a subscript i.f (or in), s. and n is commonly used and the value is usually given at the equilibrium temperature of the transformation under atmospheric pressure, or at 25 C. 

The values of AHf° and AGf° given in the tables represent the change in the appropriate thermodynamic quantity when one gram formula weight of the substance in its standard state is formed, isothermally at the indicated temperature, from the elements, each in its appropriate standard reference state. The standard reference state at 25 °C for each element has been chosen to be the standard state that is thermodynamically stable at 25 °C and 1 atm pressure. The standard reference states are indicated in the tables by the fact that the values of AHf° and AGf° are exactly zero. 

The mole (mol) is the fundamental unit describing the amount of a chemical species. The weight of a mole of a substance is its gram formula weight (fw), which is the summation of the atomic weight in grams for all the atoms in the chemical formula of the species (Skoog and West, 1982). 

Gram-atom gram formula weight mole (gram molecular weight). 

Note that it is sometimes convenient to represent a fractional number of molecules in an equation.) We see that 1 gram formula weight of KCIO3, 122.5 g, should liberate 3 gram-atoms of oxygen, 48.0 g. Hence the amount of oxygen that should be liberated from 2.00 g of potassium chlorate is X 2.00 = 0.786 g. 

Most salts, corresponding to their positive temperature coefficients of solubility, have negative heats of solution in water. For example, the heat of solution of Na SO lOH. O in water is —19 kcal per gram formula weight. The formal heat of solution of sodium chlorate is —1.3 kcal and that of NaoSO is 5.5 kcal. 

A drop of concentrated acid, which when added to a liter of pure water increases [H+] 5000-fold (from lO- to 5 X 10 ), produces an increase of [H+] of less tlian 1% (from 1.00 X lO to 1.01 X lO, for example) when added to a liter of buffered solution such as the phosphate buffer made by dissolving 0.2 gram formula weight of phosphoric acid in a liter of water and adding 0.3 gram formula weight of sodium hydroxide. 

A concentrated neutral buffer solution containing one half gram formula weight of each salt per liter may be kept in the laboratory to neutrali.e either acid or base spilled on the bod). 

Solution. The solubility of lead chloride is 9.9 g per liter at 20" C. The gram formula weight of PbCE is 278, and hence the solubility is equal to 9.9/278 or 0.0356 gfw pe liter. Lead chloride ionizes nearly completely to form lead ion and chloride ion, in dilute solution. We see that this solution contains 0.0356 moles of lead ion per liter, and, since each formula of lead chloride produces 2 chloride ions, 2 X 0.0356 = 0,0712 moles of chloride ion per liter ... 

The value obtained for x in this way is so small compared with I that we see that the approximation that has been made was justified, and that this value, 1.81 mole/1, is the value of the concentration of lead ion in the saturated solution. Each lead ion resulted from the solution of 1 molecule of lead chloride accordingly the solubility of lead chloride in this solution is 1.81 X gfw per liter. If we multiply this by the gram formula weight, 278, we obtain 0.050 g/1 as the calculated solubility of lead chloride in 1 E potassium chloride solution. This is about Vk% solubility in pure water. 

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