Solubility guidelines for ionic compounds

The solubility of a substance at a given temperature is the amount of the substance that can be dissolved in a given quantity of solvent at the given temperature. In our discussions, any substance with a solubility less than 0.01 mol/L will be referred to as insoluble. In those cases the attraction between the oppositely charged ions in the solid is too great for the water molecules to separate the ions to any significant extent the substance remains largely undissolved. 

TABLE 4.1 Solubility Guidelines for Common Ionic Compounds in Water  

Classify these ionic compounds as soluble or insoluble in water (a) sodium carbonate, Na2C03, (b) lead sul te, PbS04. 

Analyze We are given the names and formulas of two ionic compounds and asked to predict whether they are soluble or insoluble in water. 

Plan We can use Table 4.1 to answer the question. Thus, we need to focus on the anion in each compound because the table is oiganized by anions. 

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Solubility guidelines for ionic compounds in water at room temperature... 

Active Figure 9.13 Solubility guidelines for ionic compounds. If a compound contains at least one of the ions in the Solnble Compounds list, apart from the exceptions listed, it is likely to be at least moderately soluble in water. Componnds with at least one ion in the Insoluble Compounds list are poorly soluble in water (again, with the exception of the few compounds in the Exceptions list). Watch this Active Figure at http //now.brookscole.com/cracolice3e. 

The final step in predicting the outcome of such a reaction is to determine which of the products, if any, will precipitate from solution. We do this using the solubility guidelines for ionic compounds (Tables 4.2 and 4.3). The first product (NaOH) contains a Group 1A cation (Na ) and will therefore be soluble. We indicate its phase as aq). The second product (BaS04) contains the sulfate ion (SO ). Sulfate compounds are soluble unless the cation is Ag, Hg, Ca ,... 

The general guidelines for the solubility of common ionic compounds (salts) are given in Figure 14.2. These guidelines have some exceptions, but they provide a solid... 

How do you know which ionic compounds are soluble and which are not In your previous chemistry course, you learned a set of solubility guidelines. Table 9.3 summarizes these guidelines. Remember the higher guideline takes precedence. (For instance, guideline 3 says that carbonates have very low solubility. Sodium carbonate is soluble, however, because guideline 1 says that ionic compounds containing sodium are soluble.) Chemists do not usually work with solubility products for soluble compounds. Thus, you will not find soluble ionic compounds listed in tables. If you see a compound in a A p table, you know that it has a low solubility relative to compounds such as sodium chloride. 

Both silver nitrate and copper(II) nitrate are soluble ionic compounds (for solubility guidelines see page 134 and Table 4-8). 

Solution (a) Potassium phosphate and silver nitrate are both ionic compounds. Potassium phosphate contains K and PO4 - ions, so its chemical formula is K 4. Silver nitrate contains Ag and NO3- ions, so its chemical formula is AgNOs. Eiecause both reactants are strong electrolytes, the solution contains K, PO4 -, Ag and NO3- ions before the reaction occurs. According to the solubility guidelines in Table 4.1, Ag and P04 form an insoluble compound, so Ag3P04 will precipitate from the solution. In contrast, K" " and NO3- will remain in solution because KNO3 is water soluble. Thus, the balanced molecular equation for the reaction is... 

If we knew in advance which combinations of ions yield insoluble compounds, we could predict precipitation reactions. These compounds have been identified in the laboratory. Table 9.3 shows the results of such experiments for a large number of ionic compounds. Their solubilities have been summarized in a set of solubility guidelines that your instructor may ask you to memorize. These guidelines are in Active Figure 9.13. 

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