Examples formula weight

EXAMPLE 15.12. A new solid acid was prepared in a laboratory its formula weight was not known. It was titrated with standard base, and the number of moles of base was calculated. Without knowing the formula of the acid, can you tell how many moles of the acid was present in a certain mass of acid Can you tell how many equivalents of acid was present ... 

EXAMPLE 15.14. Calculate the formula weight of an acid with three replaceable hydrogen ions and an equivalent weight of 20.1 g/equivalent. assuming complete neutralization. 

What factor can be used to transform molar heat capacity into specific heat Ans. The reciprocal of atomic weight (or formula weight). For example. 

A solute in a given solvent may remain unionized (nonelectrolyte) or may ionize (electrolyte). For nonelectrolytes, 1 millimole (mmol i.e., one formula weight in mg) represents 1 mOsm. For electrolytes, osmolarity depends on the total number of particles in solution which in turn depends on the degree of dissociation of a solute. For example, 1 mmol of completely dissociated KC1 represents 2 mOsm of total particles (i.e., K+ + CT). Similarly, 1 mmol of CaCl2 represents 3 mOsm of total particles (i.e., Ca++ + CT + CT). 

For example, if there are 2.0 equivalents dissolved per liter, a solution would be referred to as 2.0 normal, or 2.0 N. The equivalent is either the same as the mole or some fraction of the mole, depending on the reaction involved, and the equivalent weight, or the weight of one equivalent, is either the same as the formula weight or some fraction of the formula weight. Normality is either the same as molarity or some multiple of molarity. Let us illustrate with acids and bases in acid-base neutralization reactions. 

In a stoichiometry calculation, the weight of one substance involved in a chemical reaction (reactant or product) is converted to the weight of another substance (reactant or product) appearing in the same reaction. The balanced equation is the basis for the calculation, and the formula weights of the reactant and product involved are needed. In the following general example,... 

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... 

Aluminum can accept two electrons to complete its octet. The pair of electrons is available from the halogen. An alkali halide can supply the electrons and form a complex (c), or the electron pair may come from the halogen of another aluminum chloride. Association with other aluminum halides accounts for the higher melting point of aluminum halides over antimony(lll) halides which have a formula weight of 95 or more. The association of aluminum sulfate, alkali metal sulfate, and water to form the stable alums is one of the more complex examples. 

The densities of ILs are also affected by the anion species. Similarly to the trends for cations, the density of ILs decreases with increasing alkyl chain length of the anion. The density of ILs is increased on the introduction of a heavy chain such as fluoroalkyl chains. For example, l-ethyl-3-methylimidazolium (EMIM) salts became heavier with the following anion species CH3SO3- < BF4 andCF COO < CF SOi < (CF3S02)2N- < (C2F5S02)2N-. It is easy to understand this order as an efFect of formula weight of the ions. However, these tendencies are still empirical, and a perfect correlation between ion structure and density is not yet available. 

Mole A mole is a measure of amount of substance. One mole is the formula weight of the substance expressed in grams. For example, for limonene, formula C10H16, the formula weight is (C = 12) (10 x 12) + (16 x 1) (H = 1) = 136 so that one mole of limonene is 136 grams of the compound. One mole of any substance contains the same number of units (atoms, molecules or ions). This is termed the Avogadro number, 6.022 x 1023 in scientific notation. 

In complexes, the term polymerization isomerism refers to the fact that a larger formula unit has the same overall composition as a smaller unit. Thus, [Pd(NH3)4][PdCl4] has the same empirical formula as [Pd(NH3)2Cl2]. With regard only to the empirical formula, [Pd(NH3)4] [PdCLt] is a polymer of the compound [Pd(NH3)2Cl2] that has one-half the formula weight but the same composition. Other examples of this type of isomerism are illustrated by the following pairs ... 

The formula mass (formula weight) of a substance is determined by adding the atomic masses (atomic weights) of each atom (not each element) in a formnla unit. Molecular mass is one type of formula mass (for substances that form molecnles) and is calculated in the same way as the formula mass for an ionic compound. For example, the formula mass of NH3 is 17.0 amu, the atomic mass of three hydrogen atoms plus that of one nitrogen atom. Three or more significant digits should be used to report formula masses. (Section 7.1)... 

Some substances exist as a collection of ions rather than as separate mol- ecules. An example is ordinary table salt, sodium chloride (NaCl), which is composed of an array of Na+ and Cl- ions. There are no NaCl molecules present. However, in this text, for convenience, we will apply the term molar mass to both ionic and molecular substances. Thus we will refer to 58.44 (22.99 + 35.45) as the molar mass for NaCl. In some texts the term formula weight is used for ionic compounds instead of the terms molar mass or molecular weight. ... 

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. 

---