Ionic compounds molarity

When discussing solutions of ionic compounds, molarity emphasizes the number of individual ions. A one molar solution of Na+ contains Avogadro s number, 6.022 X 10, of Na per liter. In contrast, equivalents per liter emphasize charge one equivalent of Na+ contains Avogadro s number of positive charge. 

The solubility product depends on the temperature, and at a given temperature it is constant for a particular ionic compound. Molar solubility is defined as the number of moles of solute dissolved in one liter of its saturated solution. Using the molar solubility of a compound, the solubility product of that compound can be determined or vice versa. 

The reverse of Example 16.4 involves finding Rq, of a compound given its solubility. The solubilities of many ionic compounds are determined experimentally and tabulated in chemical handbooks. Most solubility values are given in grams of solute dissolved in 100 grams of water. To obtain the molar solubility in moles/L, we have to assume that the density of the solution is equal to that of water. Then the number of grams of solute per 100 g water is equal to the number of grams of solute per 100 mL of solution. This assumption is valid because the mass of the compound in solution is small. To solve for IQp, find the molar solubility of the solute and determine the concentration of its component ions. Substitute into the IQp expression. 

The molar mass of a molecular compound is the mass per mole of its molecules. The molar mass of an ionic compound is the mass per mole of its formula units. 

Le Chatelier s principle is a powerful tool for explaining how a reaction at equilibrium shifts when a stress is placed on the system. In this experiment, you can use Le Chatelier s principle to evaluate the relative solubilities of two precipitates. By observing the formation of two precipitates in the same system, you can infer the relationship between the solubilities of the two ionic compounds and the numerical values of their solubility product constants (K ). You will be able to verify your own experimental results by calculating the molar solubilities of the two compounds using the Ksp for each compound. 

Calculate the molar solubilities of the two ionic compounds from their Ksp values. 

A.V. (1997) Adsorption of a corticoid on colloidal hematite particles of different geometries. J. Colloid Interface Sd. 187 429-434 Verdonck, L. Hoste, S. Roelandt, F.F. Van der Kelen, G.P. (1982) Normal coordinate analysis of a-FeOOH - a molecular approach. J. Molecular Structure 79 273-279 Vermilyea, D.A. (1966) The dissolution of ionic compounds in aqueous media. J. Electro-chem. Soc. 113 1067-1070 Vermohlen, K. Lewandowski, H. Narres, H-D. Schwager, M.S. (2000) Adsorption of polyelectrolytes onto oxides - the influence of ionic strength, molar mass and Ca " ions. Coll. Surf. A 163 45-53... 

Chemists may distinguish between the molar masses of pure elements, molecular compounds, and ionic compounds by referring to them as the gram atomic mass, gram molecular mass, and gram formula mass, respectively. Don t be fooled The basic concept behind each term is the same molar mass. 

The Kelvin equation may also be applied to the equilibrium solubility of a solid in a liquid. In this case the ratio p/p0 in Equation (40) is replaced by the ratio a/a0, where a0 is the activity of dissolved solute in equilibrium with a flat surface, and a is the analogous quantity for a spherical surface. For an ionic compound having the general formula MmXn, the activity of a dilute solution is related to the molar solubility S as follows ... 

The molar mass of an element is the mass per mole of its atoms the molar mass of a molecular compound is the mass per mole of its molecules the molar mass of an ionic compound is the mass per mole of its formula units. The units of molar mass in each case are grams per mole (g-moD1). 

The molar masses of molecular and ionic compounds are calculated from the molar masses of the elements present the molar mass of a compound is the sum of the molar masses of the elements that make up the molecule or the formula unit. We need only note how many times each atom or ion appears in the molecular formula or the formula unit of the ionic compound. For example, the molar mass of the ionic compound Na2S04 is... 

What is a synonym for molar mass (a) for molecules (b) for atoms (c) for ionic compounds What is a synonym for formula mass (d) for molecules (e) for atoms (f) for ionic compounds ... 

The maximum molarity possible in an aqueous solution of an ionic compound is about 40 M (with LiC103 as the solute). Pure water itself contains 55.6 mol/L. Sometimes, knowing the maximum molarity is important for determining whether a calculated answer is reasonable, or for other purposes. 

As shown in Section 11.1, the molarities of ionic compounds can be calculated just as the molarities of covalent compounds are. The molarity of an ionic compound is the number of moles of the compound per liter of solution. However, as discussed in Chapter 9, it is often useful to describe ionic compounds in solution as the separate ions. The molarity of any ion is simply the number of moles of that ion per liter of solution. 

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. ... 

In dilute aqueous solutions, it has been demonstrated experimentally for poorly soluble ionic salts (solubilities less than 0.01 molL ) that the mathematical product of the total molar concentrations of the component ions is a constant at constant temperature. This product, is called the solubility product. Thus for a saturated solution of a simple ionic compound AB in water, we have the dynamic equilibrium ... 

Scientists also use the simplest formula to represent one mole of an ionic compound. They often use the term formula unit when referring to ionic compounds, because they are not found as single molecules. A formula unit of an ionic compound represents the simplest ratio of cations to anions. A formula unit of KBr is made up of one ion and one Br ion. One mole of an ionic compound has 6.022 x 10 of these formula units. As with molecular compounds, the molar mass of an ionic compound is the sum of the masses of all the atoms in the formula expressed in g/mol. Table 1 compares the formula units and molar masses of three ionic compounds. Sample Problem F shows how to calculate the molar mass of barium nitrate. 

Table 2 Calculating Molar Mass for Ionic Compounds ...

Why is the simplest formula used to determine the molar mass for ionic compounds ... 

Notice in Table 1 that the same about 25 joule rule also applies to the molar heat capacities of solid ionic compounds. One mole barium chloride has three times as many ions as atoms in 1 mol of metal. So, you expect the molar heat capacity for BaCl2 to be C = 3 x 25 J/K mol. The value in Table 1,75.1 J/K mol, is similar to this prediction. 

O What is the relationship between the number of atoms per unit of an ionic compound and its molar heat capacity ... 

Determine the molar mass of each of the following ionic compounds NaOH, CaCl2, KC2H3O2, Sr(N03)2, and (NH4)3P04. 

You have learned that the solubility product constant can be used to determine the molar solubility of an ionic compound. You can apply this information as you do the CHEMLAB at the end of this chapter. also can be used to find the concentrations of the ions in a saturated solution. 

You can calculate the molar solubility of an ionic compound using the solubility product constant expression. 

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