Formula weight,

Chemical formulas and chemical equations both have a quantitative significance in that the subscripts in formulas and the coefficients in equations represent precise quantities. The formula H2O indicates that a molecule of this substance (water) contains exactly two atoms of hydrogen and one atom of oxygen. Similarly, the coefficients in a balanced chemical equation indicate the relative quantities of reactants and products. But how do we relate the numbers of atoms or molecules to the amounts we measure in the laboratory Although we cannot directly count atoms or molecules, we can indirectly determine their numbers if we know their masses. Therefore, before we can pursue the quantitative aspects of chemical formulas and equations, we must examine the masses of atoms and molecules. 

The formula weight of a substance is the sum of the atomic weights of the atoms in the chemical formula of the substance. Using atomic weights, we find, for example, that the formula weight of sulfuric acid (H2SO4) is 98.1 amu  

For convenience, we have rounded off the atomic weights to one decimal place, a practice we will follow in most calculations in this book. 

If the chemical formula is the chemical symbol of an element, such as Na, the formula weight equals the atomic weight of the element, in this case 23.0 amu. If the chemical formula is that of a molecule, the formula weight is also called the molecular weight. The molecular weight of glucose (CgHi20g), for example, is 

Calculate the formula weight of (a) sucrose, C12H22O1, (table sugar), and (b) cakium nitrate, Ca(N03)2. 

Combustion reactions are rapid reactions that produce a flame. Most combustion reactions we observe involve O2 from air as a reactant. Equation 3.5 illustrates a general class of reactions involving the burning, or combustion, of hydrocarbons (compounds that contain only carbon and hydrogen, such as CH4 and C2H4). txx (Section 2.9) 

Does this reaction produce or consume thermal energy (heat)  

The state of the water in this reaction, H20( ) or H20(/), depends on the reaction conditions. Water vapor, H20( ), is formed at high temperature in an open container. 

Liquid propane in the tank, C3H8, vaporizes and mixes with air as it escapes through the nozzle. The combustion reaction of CgHg and O2 produces a blue flame. 

EXERCISE 3.4 Writing Balanced Equations for Combustion Reactions 

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Formula weights are based upon the International Atomic Weights of 1993 and are computed to the nearest hundredth when justified. The actual significant figures are given in the atomic weights of the individual elements. 

Solubility is given in parts by weight (of the formula weight) per 100 parts by weight of the solvent (i.e., percent by weight) and at room temperature. Another unit frequently used is grams per 100 mF of solvent (mF per 100 mF for liquids and gases). The symbols of the common mineral acids represent aqueous solutions of these acids. 

Name Formula Formula weight Density Melting point, °C Boiling point, °C Solubility in 100 parts solvent... 

H0CH3)3CNHH3 121.137 Tris(hydroxymethyl)aminomethane is available commercially as a primary standard. Dry at 100-103°C (<110°C). In titrations with a strong acid the equivalence point is at about pH 4.5-5. Equivalent weight is the formula weight. [J. H. Eossum, P. C. Markunas, and J. A. Riddick, Anal. Chem., 23 491 (1951).]... 

Heat reagent-grade material for 1 hr at 255-265°C. Cool in an efficient desiccator. Titrate sample with acid to pH 4-5 (first green tint of bromocresol green), boil the solution to eliminate the carbon dioxide, cool, and again titrate to pH 4-5. Equivalent weight is one-half the formula weight. 

Accurately weigh about 6 g NaCl and dissolve in distilled water. Pass the solution through a well-rinsed cation exchange column (Dowex 50W) in the hydrogen form. The equivalent amount of HCl is washed from the column (in 10 column volumes) into a volumetric flask and made up to volume. Equivalent weight is the formula weight. 

Reagent Formula Weight Density, g mL-i (20°C) Weight % (approx) Molarity V, mL ... 

Descriptive properties for a basic group of approximately 1400 inorganic compounds are compiled in Section 3. These follow a concise, revised introduction to inorganic nomenclature that follows the recommendations of the lUPAC published in 1990. In this section are given the exact atomic (or formula) weight of the elements accompanied, when available, by the uncertainty in the final figure given in parentheses. 

Analytical scheme outlined by Hillebrand and Lundelh for the gravimetric analysis of Ni in ores (DMG = dimethylgloxime). The factor of 0.2031 in the equation for %Ni accounts for the difference in the formula weights of Ni(DMG)2 and Ni see Chapter 8 for more details. 

Normality is the number of equivalent weights (EW) per unit volume and, like formality, is independent of speciation. An equivalent weight is defined as the ratio of a chemical species formula weight (FW) to the number of its equivalents... 

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