Electrolytes insoluble ionic compounds

Now let us look at the product side of the equation. One product is the precipitate CaC03(.s). According to the solubility rules, this is an insoluble ionic compound so it will exist in water as a solid. We leave the formula as CaC03(s) to convey this information in the equation. On the othCT hand, NaOH is a soluble ionic substance and therefore a strong electrolyte it dissolves in aqueous solution to give the freely moving ions, whieh we denote by writing Na (a ) + OH (a ). The complete equation is... 

The purpose of such a complete ionic equation is to represent each substance by its predominant form in the reaction mixture. For example, if the substance is a soluble ionic compound, it probably dissolves as individual ions (so it is a strong electrolyte). In a complete ionic equation, you represent the compound as separate ions. If the substance is a weak electrolyte, it is present in solution primarily as molecules, so you represent it by its molecular formida. If the substance is an insoluble ionic compound, you represent it by the formula of the compound, not by the formulas of the separate ions in solution. 

Is an insoluble ionic compound, such as AgCI, a strong electrolyte or a weak electrolyte ... 

Some ionic compounds are soluble, others are not. Consider what happens when we pour a solution of sodium chloride (a strong electrolyte) into a solution of silver nitrate (another strong electrolyte). A solution of sodium chloride contains Na+ cations and Cl anions. Similarly, a solution of silver nitrate, AgNO, contains Ag+ cations and NO, anions. When we mix these two aqueous solutions, a white precipitate, a cloudy, finely divided solid deposit, forms immediately. Analysis shows that the precipitate is silver chloride, AgCl, an insoluble white solid. The... 

The properties of ionic compounds in solution are actually the properties of the individual ions themselves (Figure 9.1). These compounds are called strong electrolytes because their solutions conduct electricity well. For example, an aqueous solution of sodium chloride consists essentially of sodium ions and chloride ions in water. A similar solution of calcium chloride consists of calcium ions and chloride ions in water. If either solution is treated with a solution containing silver ions, the chloride ions will form silver chloride, which is insoluble. The chloride ions act independently of the cation that is also present, regardless of whether it is sodium ion, calcium ion, or any other ion. Because the properties of the compound are the properties of the component ions, we need to learn to write equations for only the ions that react, omitting the ions that remain unchanged throughout the reaction (Section 9.2). 

The term metathesis literally means to transpose. The term double replacement is often used to describe these reactions because the cations switch places with each other. These are chemical reactions that involve an exchange of positive ions between two compounds and that generally take place between two ionic compounds in an aqueous solution. The driving force that causes these reactions to occur is a decrease in the number of ions from the reactants to products. This will occur when a stable product forms from the ionic reactants. The three types of stable products that can form are a precipitate (or an insoluble solid), a gas (gaseous materials will bubble out of the solutions and leave the reaction mixture), or a stable molecule (a weak electrolyte, or nonelectrolyte, such as water). A general equation for a double-replacement reaction is... 

How can we predict whether a precipitate will form when a compound is added to a solntion or when two solutions are mixed It depends on the solubility of the solute, which is defined as the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. Chemists refer to substances as soluble, slightly soluble, or insoluble in a qualitative sense. A substance is said to be soluble if a fair amount of it visibly dissolves when added to water. If not, the substance is described as slightly soluble or insoluble. All ionic compounds are strong electrolytes, but they are not equally soluble. 

To predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes, we must (1) note the ions present in the reactants, (2) consider the possible cation-anion combinations, and (3) use Table 4.1 to determine if any of these combinations is insoluble. For example, will a precipitate form when solutions of Mg(N03)2 and NaOH are mixed Both substances are soluble ionic compounds and strong electrolytes. Mixing the solutions first produces a solution containing Mg, N03, Na, and OH ions. Will either cation interact with either anion to form an insoluble compound Knowing from Table 4.1 that Mg(N03)2 and NaOH are both soluble in water, our only possibilities are Mg " with OH and Na with N03. From Table 4.1 we see that hydroxides are generally insoluble. Because Mg " " is not an exception, Mg(OH)2 is insoluble and thus forms a precipitate. NaN03, however, is soluble, so Na" " and NO3 remain in solution. The balanced equation for the precipitation reaction is... 

In a complete ionic equation, only dissolved strong electrolytes (such as soluble ionic compounds) are written as separate ions. As the (aq) designations remind us, CaCl2, Na2C03, and NaCl are all dissolved in the solution. Furthermore, they are all strong electrolytes. CaC03 is an ionic compound, but it is not soluble. We do not write the formula of any insoluble compound as its component ions. Thus, the complete ionic equation is... 

To predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes, we must (1) note the ions present in the reactants, (2) consider the possible cation-anion combinations, and (3) use Table 4.1 to determine if any of these combinations is insoluble. For example, will a precipitate form when solutions of Mg(N03)2 and NaOH are mixed Both substances are soluble ionic compounds and strong electrolytes. Mixing the solutions first produces a solution containing... 

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... 

Let ns snmmarize the main points in this section. Compounds that dissolve in water are soluble those that dissolve little, or not at all, are insoluble. Soluble substances are either electrolytes or nonelectrolytes. Nonelectrolytes form noncon-dncting aqneons solutions because they dissolve completely as molecules. Electrolytes form electrically conducting solutions in water because they dissolve to give ions in solntion. Electrolytes can be strong or weak. Almost all soluble ionic substances are strong electrolytes. Soluble molecular substances usually are nonelectrolytes or weak electrolytes the latter solution consists primarily of molecules, but has a small percentage of ions. Ammonia, NH3, is an example of a molecular substance that is a weak electrolyte. A few molecular substances (such as HCl) dissolve almost entirely as ions in the solution and are therefore strong electrolytes. The solubility rules can be used to predict the solubility of ionic compounds in water. 

You will need to convert the molecular equation to the complete ionic equation, then cancel spectator ions to obtain the net ionic equation. For each ionic compound in the reaction, use the solubility rules to determine if the compound will be soluble (in the solution as ions) or insoluble (present as an undissolved solid). For the complete ionic equation, represent all of the strong electrolytes by their separate ions in solution, adding (aq) after the formula of each. Retain the formulas of the other compounds. An ionic compound should have (aq) after its formula if it is soluble or (s) if it is insoluble. 

SFfo covalent CIF,. covalent. 8.81 KF is an ionic compound. It is a solid at room temperature made up of K" and F ions. It has a high melting point, and it is a strong electrolyte. Benzene. CftH. is a covtdent compound that exists as discrete molecules. It is a liquid at room temperature. It has a low melting point, is insoluble in water, and is a nonelectrolyte. 

The properties of completely alkylated or arylated metal compounds often differ widely from those of the usual derivatives of metals and resemble those of wholly organic compounds in many respects. For instance, very many of them are volatile, insoluble in water, and miscible with organic solvents and do not conduct an electric current. The derivatives of strongly electropositive elements, however, such as those of alkali metals, are markedly ionic, involatile, solid, almost insoluble in organic solvents, and moreover, good electrolytes. 

Rust is a brown, insoluble compound of formula Fe203 -xH20 (the x in the formula indicates that it has a variable composition) which is formed when iron reacts with air and water. Rusting requires the presence of oxygen, water and ionic substances dissolved in the water (electrolytes). In the absence of any one of these, little rusting will occur. 

To avoid the cost and disposal problems of once-through processes employing alkali metal compounds, a considerable amount of research and development effort has been expended on techniques for regenerating this type of absorbent. Processes used employ precipitation of insoluble compounds (double alkali), and thermal decomposition (Wellman-Lord and Elsorb). Processes under development or which have been investigated include precipitation of insoluble compounds (zinc oxide), low-temperature reduction of sulfite (citrate and potassium formate processes), high-temperature reduction (aqueous carbonate process), electro-dialysis (SOXAL), and electrolytic (Stone Webster/Ionics Process). Descriptions of some of these processes are provided in subsequent sections. 

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