Precipitation reactions Forming solids

In single displacement reactions (see the preceding section), only one chemical species is displaced. In double displacement reactions, or metathesis reactions, two species (normally ions) are displaced. Most of the time, reactions of this type occur in a solution, and either an insoluble solid (in precipitation reactions) or water (in neutralization reactions) will be formed. 

The formation of an insoluble solid in a solution is called precipitation. For instance, if you mix a solution of potassium chloride and a solution of silver nitrate, a white insoluble solid forms in the resulting solution. Here are the molecular, ionic, and net-ionic equations for this double-displacement reaction  

The white insoluble solid that forms (AgCl) is silver chloride. You CcUi drop out the potassium cation and nitrate anion spectator ions, because they don t change during the reaction cmd are found on both sides of the equation in an identical form. (See the earlier section Writing ionic and net-ionic equations for details on spectator ions.) 

To write these equations, you have to know something about the solubility of ionic compounds  

If a compound is insoluble, it will precipitate (form a solid). 

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An excellent example combining thermodynamics, kinetics, and equilibrium considerations was presented by O Day (1999), who considered the precipitation reaction of solid lead carbonate, in the form of the mineral cerussite (PbCOj ) according to the reaction... 

Precipitation reaction A solid or precipitate forms upon mixing two aqueous solutions. 

In a precipitation reaction, a solid (precipitate) forms when the reactants are combined. In such a reaction, the mixture turns cloudy as the reactants are combined and a soUd settles out on standing. For example, if you mixed solutions of barium nitrate and sodium carbonate, a precipitate of barium carbonate would form. 

Apply the test to compounds which contain chlorine or bromine. If the compound is a solid, dissolve 0 1 g. in the minimum volume of pure, dry acetone. To 1 ml. of the sodium iodide acetone reagent add 2 drops of the compound (if a hquid) or the acetone solution (if a sohd). Shake and allow to stand at room temperature for 3 minutes. Note whether a precipitate is formed and also whether the solution acquires a reddish-brown colour (liberation of iodine). If no change takes place at rocrm temperature, place the test-tube in a beaker of water at 50°. After 5 minutes, cool to room temperature, and observe whether a reaction has occurred. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Scoops of solid potassium tcrt-butoxide (purchased from E. Merck, Darmstadt, and specified to be at least 95% pure) were added over 20-30 minutes by temporarily removing the drying tube. At the beginning of the reaction much heat is evolved therefore the base should be added in small portions in order to keep the temperature below 10°. During the addition of the base, a precipitate is formed. 

In a 200-ml, three-necked flask equipped with a mechanical stirrer, a thermometer, and a gas-inlet tube are placed 41.2 g. (0.2 mole) of 2,6-di- er/-butylphenol (Note 1) in 75 ml. of dimethylformamide (Note 2) and 2.5 g. (0.0075 mole) of salcomine (Note 3). With stirring, oxygen is introduced at such a rate that the temperature does not exceed 50°. This is continued for 4 hours. At the end of the reaction the temperature drops to about 25°. The reaction mixture is then poured onto 500 g. of crushed ice and 15 ml. of 4N hydrochloric acid. A yellow-brown precipitate is formed. The solid material is collected by suction filtration and washed on the filter three times with 50-ml. portions of IN hydrochloric... 

A mixture of 30 parts of 17o -ethvnvl-19-norandrost-4-ene-30,17(3-diol, 360 parts of dry pyridine, and 111 parts of acetic anhydride, under nitrogen, is stirred and heated at the reflux temperature for about 5 hours. This reaction mixture is cooled, then poured into approximately 3,500 parts of cold water and the resulting aqueous mixture is stirred at room temperature for about 0.5 hour. The precipitate which forms is collected by filtration, then is washed on the filter with water and dried in air. This solid material is extracted into ether, and the ether solution is washed successively with 10% aqueous hydrochloric acid and 5% aqueous sodium bicarbonate. 

A mixture containing 186 g (0.20 mol) of 2-aminopyridine, 0.55 g of lithium amide and 75 cc of anhydrous toluene was refluxed for 1.5 hours. Styrene oxide (12.0 g = 0.10 mol) was then added to the reaction mixture with stirring over a period of ten minutes. The reaction mixture was stirred and refluxed for an additional 3.5 hours. A crystalline precipitate was formed during the reaction which was removed by filtration, MP 170°C to 171°C, 1.5 g. The filtrate was concentrated to dryness and a dark residue remained which was crystallized from anhydrous ether yield 6.0 g. Upon recrystallization of the crude solid from 30 cc of isopropyl alcohol, 2.0 g of a light yellow solid was isolated MP 170°C to 171°C. 

A solution of 100 g (1.7 mols) of isopropylamine in 60 cc of water was stirred into a solution of 4-hydroxyphenoxypropylene oxide. After the exothermic reaction has subsided, the reaction mixture was heated for two hours at 60Thereafter, the aqueous ethanol was distilled off, and the solid residue was dissolved in aqueous hydrochloric acid comprising more than the theoretical stoichiometric molar equivalent of hydrochloric acid. The aqueous acid solution was extracted with ether and was then made alkaline with sodium hydroxide, whereby a solid crystalline precipitate was formed which was filtered off and dried over phosphorus pentoxide. The product was 1,1 -(4 -hvdroxvphenoxv)-2-hvdroxv-3-isopropylamino-pro-pane. Its hydrochloride had a melting point of 166°Cto 169°C. 

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. 

Precipitation reactions, like all reactions, reach a position of equilibrium. Suppose, for example, solutions of Sr(N03)2 and K2Cr04 are mixed. In this case, Sr2+ ions combine with Cr042- ions to form a yellow precipitate of strontium chromate, SrCr04 (Figure 16.1). Very quickly, an equilibrium is established between the solid and the corresponding ions in solution ... 

Precipitate A solid that forms when two solutions are mixed, 78 Precipitation diagram, 78 Precipitation reaction Formation of an insoluble solid when two electrolyte solutions are mixed, 78,95-96q diagram, 78... 

In the lead-acid battery, the reactions at both electrodes include the dissolved state, which means that the reacting species are dissolved in the course of the reaction. The new chemical compounds formed during the reaction are precipitated again as solid matter. This explains the completely different appearance of the material in the charged and discharged states. 

When we mix two solutions the result is often simply a new solution that contains both solutes. However, in some cases the solutes can react with each other. For instance, when we mix a colorless aqueous solution of silver nitrate with a clear yellow aqueous solution of potassium chromate, a red solid forms, indicating that a chemical reaction has occurred (Fig. 1.1). This section and the next two introduce three of the main types of chemical reactions precipitation reactions, acid-base reactions, and redox reactions, all of which are discussed in more depth in later chapters. (The fourth type of reaction discussed in this text, Lewis acid-base reactions, is introduced in Section 10.2.) Because many chemical reactions take place in solution, particularly in water, in this section we begin by considering the nature of aqueous solutions. 

In a precipitation reaction, an insoluble solid product forms when we mix two electrolyte solutions. When an insoluble substance is formed in water, it immediately precipitates. In the chemical equation for a precipitation reaction, we use (aq) to indicate substances that are dissolved in water and (s) to indicate the solid that has precipitated ... 

The importance of one other type of reaction that metal ions undergo has been recognized and studied extensively in the past 40 years. This reaction is adsorption, in which metal ions bind to the surface of particulate matter and are thereby transported as part of a solid phase even though they do not form an identifiable precipitate. Conceptually, these reactions can be thought of as hybrids between complexation and precipitation reactions. Most studies of these reactions have used metal oxides or hydroxides as the solid (adsorbent) phase, and the... 

The diversity of chemical reactions is immense. To make sense of this vast expanse of chemistry, we need a system for grouping chemical reactions into categories. The reactions within each category should share some characteristics or follow a common theme. One relatively simple category is precipitation reactions, in which cations and anions in aqueous solution combine to form neutral insoluble solids. 

The simplest balanced chemical equation for a precipitation reaction is a net ionic equation that has ions as the reactants and a neutral solid as the product. In a precipitation reaction, reactant ions combine to form a neutral ionic solid. One reactant carries positive charge and the other carries negative charge, but the product is electrically neutral. Because electrical charge always is conserved, the total positive charge of the reacting cations... 

C16-0026. Figure 16-12Z> shows the precipitation reaction to form AgBr. Calculate the amount of AgBr solid that forms and the concentrations of Ag and Br" ions remaining in solution if 0.500 L each of 1.00 M solutions of AgN03 and KBr are mixed together. 

Depending on electrolyte composition, the metal will either dissolve in the anodic reaction, that is, form solution ions [reaction (1.24)], or will form insoluble or poorly soluble salts or oxides precipitating as a new solid phase next to the electrode surface [reaction (1.28)]. Reacting metal electrodes forming soluble products are also known as electrodes of the first kind, and those forming solid products are known as electrodes of the second kind. 

When the water is too alkaline, swimmers experience similar physical discomfort—burning eyes and nose and itchy, dry skin. The effect on the pool, however, is different. When water is alkaline, calcium dissolved in the pool water can precipitate (fall) out of solution. A precipitate is a solid that forms from a solution due to a chemical reaction. This solid creates unsightly scales on the sides of the pool. Like water that is too acidic, alkaline water also affects the efficiency of the chlorine. More chlorine needs to be added to alkaline water to effectively disinfect the pool. Over time, a swimming pool that is not kept at a neutral pH can become very expensive to maintain. 

Species with low solubility in water may exist in solid form (e.g., Ag2S, BaS()4) or liquid form (e.g., chlorinated solvents). Precipitation reactions and immiscible-phase separation are important processes affecting this type of speciation. 

In the first reaction, two ionic compounds in water are mixed. The AgCl formed by the swapping of anions is insoluble, causing the reaction to proceed. The solid AgCl formed from solution is an example of a precipitate. In the second reaction, a covalent compound, HzO, is formed from its ions in solution, H+ and OH, causing the reaction to proceed. In the third reaction, a solid reacts with the acid in solution to produce two covalent compounds. 

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