Water ionic compounds

We can often decide whether a substance is an ionic compound or a molecular compound by examining its formula. Binary molecular compounds are typically formed from two nonmetals (such as hydrogen and oxygen, the elements in water). Ionic compounds are typically formed from the combination of a metallic element with nonmetallic elements (such as the combination of potassium with sulfur and oxygen to form potassium sulfate, K2S04). Ionic compounds typically contain one metallic element the principal exceptions are compounds containing the ammonium ion, such as ammonium nitrate, which are ionic even though all the elements present are nonmetallic. 

Some compounds are composed entirely of ions. These compounds are called salts. The ions in most ionic compounds can be separated by melting or dissolving them in water. When melted or dissolved in water, ionic compounds are good conductors of electricity. Most ionic compounds have high melting points and tend to be brittle. 

Solid phases of binary systems, like the liquid phases, are very commonly of variable composition. Here, as with the liquid, the stable range of composition is larger, the more similar the two components are. This of course is quite c-ontrary to the chemists notion of definite chemical composition, definite structural formulas, etc., but those notions are really of extremely limited application. It happens that the solid phases in the system water—ionic compound are often of rather definite composition, and it is largely from this rather special case that the idea of definite compositions in solids has become so firmly rooted. In such a system, there are normally two solid phases ice and the crystalline ionic compound. Ice can take up practically none of any ionic compound, so that it has practically no range of compositions. And many ionic crystals... 

Charged particles must be free to move for a material to conduct an electric current. In the solid state, ionic compounds are nonconductors of electricity because of the fixed positions of the ions. However, in a liquid state or when dissolved in water, ionic compounds are electrical conductors because the ions are free to move. An ionic compound whose aqueous solution conducts an electric current is called an electrolyte. You will learn more about solutions of electrolytes in Chapter 15. 

Polar Nature of Water Ionic Compounds in Water Covalent Compounds in Water... 

Many of the reactions of interest in the course you are taking occur between compounds or elements dissolved in water. Ionic compounds and some polar covalent compounds break apart (dissociate) into ions when they are dissolved in water. Thus, a water solution of sodium hydroxide (NaOH), an ionic compound, does not contain molecules of NaOH but, rather, contains equal numbers of sodium ions (Na ) and hydroxide ions (OH ). Covalently bonded hydrogen chloride, HCl, dissolves readily in water to form and Cr ions. Equations for reactions between substances that form ions in solution can be written in several ways. For example. Equation 5.22 contains three substances that form ions, HCl, NaOH, and NaCl. Equation 5.22 is written in the form of a molecular equation in which each compound is represented by its formula. This same reaction, when represented by a total ionic equation, becomes... 

In the cases considered so far, both ions have been so weakly acidic or basic that we have been able to assume that none of them is removed by reaction with water. Ionic compounds with a basic anion and/or an acid cation are much more common. The carbonates, phosphates, sulfides, fluorides, acetates, and other organic acid anions all take protons in water to reduce the concentration of the anion and... 

As you have iearned, solid compounds can be ionic or moiecular. In an ionic soiid, a crystal structure is made up of charged particles held together by ionic attractions. In a molecular solid, molecules are composed of covalently bonded atoms. The solid is held together by noncovalent, intermolecular forces. When they dissolve in water, ionic compounds and molecular compounds behave differently. 

It is soluble in organic solvents (a characteristic of a covalent compound). but dissolves in water and can form hydrates (a characteristic of an ionic compound), hence the hydrated must be... 

These chlorozincates must not be confused with the non-ionic compounds which quinoline and aniline bases give with neutral zinc chloride the latter have the formulae [(C,H7N)2ZnClt] and [(C,H7N)tZnCl ] respectively, and both are only slightly soluble in water. 

Solvent Effects on the Rate of Substitution by the S 2 Mechanism Polar solvents are required m typical bimolecular substitutions because ionic substances such as the sodium and potassium salts cited earlier m Table 8 1 are not sufficiently soluble m nonpolar solvents to give a high enough concentration of the nucleophile to allow the reaction to occur at a rapid rate Other than the requirement that the solvent be polar enough to dis solve ionic compounds however the effect of solvent polarity on the rate of 8 2 reactions IS small What is most important is whether or not the polar solvent is protic or aprotic Water (HOH) alcohols (ROH) and carboxylic acids (RCO2H) are classified as polar protic solvents they all have OH groups that allow them to form hydrogen bonds... 

Ionic compounds often separate from water solution with molecules of water incorporated into the solid. Such compounds are referred to as hydrates. An example is hydrated copper sulfate, which contains five moles of H20 for every mole of CuS04. Its formula is CuS04- 5H20 a dot is used to separate the formulas of the two compounds CuS04 and H20. A Greek prefix is used to show the number of moles of water the systematic name of CuS04- 5H20 is copper(ll) sulfate pentahydrate. 

A 5.025-g sample of calcium is burned in air to produce a mixture of two ionic compounds, calcium oxide and calcium nitride. Water is added to this mixture. It reacts with calcium oxide to form 4B32 g of calcium hydroxide. How many grams of calcium oxide are formed How many grams of calcium nitride ... 

Sometimes when water solutions of two different ionic compounds are mixed, an insoluble solid separates out of solution. The precipitate that forms is itself ionic the cation comes from one solution, the anion from the other. To predict the occurrence of reactions of this type, you must know which ionic substances are insoluble in water. 

Many, but not all, ionic compounds (e.g., NaCl but not CaC03) are soluble in water, a polar solvent In contrast, ionic compounds are insoluble in nonpolar solvents such as benzene (C6H6) or carbon tetrachloride (CCI4). 

As we noted in Chapter 4, the solubility of ionic compounds in water varies tremendously from one solid to another. The extent to which solution occurs depends on a balance between two forces, both electrical in nature ... 

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. 

Let us apply these ideas to the third-row elements. On the left side of the table we have the metallic reducing agents sodium and magnesium, which we already know have small affinity for electrons, since they have low ionization energies and are readily oxidized. It is not surprising, then, that the hydroxides of these elements, NaOH and Mg(OH)z, are solid ionic compounds made up of hydroxide ions and metal ions. Sodium hydroxide is very soluble in water and its solutions are alkaline due to the presence of the OH- ion. Sodium hydroxide is a strong base. Magnesium hydroxide, Mg(OH)2, is not very soluble in water, but it does dissolve in acid solutions because of the reaction... 

In general, the compounds best separated by LSC are those which are soluble in organic solvents and are non-ionic. Water soluble non-ionic compounds are better separated using either reverse-phase or bonded-phase chromatography. 

In general, binary compounds of two nonmetals are molecular, whereas binary compounds formed by a metal and a nonmetal are ionic. Water (H20) is an example of a binary molecular compound, and sodium chloride (NaCl) is an example of a binary ionic compound. As we shall see, these two types of compounds have... 

Ionic compounds are named by starting with the name of the cation (with its oxidation number if more than one charge is possible), followed by the name of the anion hydrates are named by adding the word hydrate, preceded by a Greek prefix indicating the number of water molecules in the formula unit. 

Table 1.1 summarizes the solubility patterns of common ionic compounds in water. Notice that all nitrates and all common compounds of the Group 1 metals are soluble so they make useful starting solutions for precipitation reactions. Any spectator ions can be used, provided that they remain in solution and do not otherwise react. For example, Table 1.1 shows that mercury(I) iodide, Hg2I2, is insoluble. It is formed as a precipitate when solutions containing Hg22+ ions and I ions are mixed ... 

Use the information in Table 1.1 to classify each of the following ionic compounds as soluble or insoluble in water ... 

For each of the following reactions, suggest two soluble ionic compounds that, when mixed together in water, result in the net ionic equation given ... 

The reaction between an acid and a base is called a neutralization reaction, and the ionic compound produced in the reaction is called a salt. The general form of a neutralization reaction of a strong acid and a metal hydroxide that provides the hydroxide ion, a strong base, in water is... 

Basic oxides are ionic compounds, such as CaO, that also react with acids to give a salt and water. For instance, magnesium oxide, a basic oxide, reacts with hydrochloric acid ... 

Why Do We Need to Know This Material The techniques described in this chapter provide rhe tools that we need to analyze and control the concentrations of ions in solution. A great deal of chemistry is carried out in solution, and so this material is fundamental to understanding chemistry. The ionic compounds released into waterways by individuals, industry, and agriculture can impair the quality of our water supplies. However, these hazardous ions can be identified and removed if we add the right reagents. Aqueous equilibria govern the stabilization of the pH in blood, seawater, and other solutions encountered in biology, medicine, and the environment. 

Because the fluoride ion is so small, the lattice enthalpies of its ionic compounds tend to be high (see Table 6.6). As a result, fluorides are less soluble than other halides. This difference in solubility is one of the reasons why the oceans are salty with chlorides rather than fluorides, even though fluorine is more abundant than chlorine in the Earth s crust. Chlorides are more readily dissolved and washed out to sea. There are some exceptions to this trend in solubilities, including AgF, which is soluble the other silver halides are insoluble. The exception arises because the covalent character of the silver halides increases from AgCl to Agl as the anion becomes larger and more polarizable. Silver fluoride, which contains the small and almost unpolarizable fluoride ion, is freely soluble in water because it is predominantly ionic. 

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