A double replacement reaction occurs when parts of two ionic compounds are exchanged, making two new compounds.
There are three ways of representing a precipitation reaction, using a molecular equation, complete ionic equation or net ionic equation, as described in section 6.1.ġ. The formation of the solid is the DRIVING FORCE of the reaction (the factor that makes the reaction go).Ī precipitation reaction can be predicted to occur with the help of a solubility table (Table 1). A precipitation reaction, therefore, is predicted to occur, as described by the following equations: The solubility table indicate all nitrate salts are soluble but that AgF is one of the exceptions to the general solubility of fluoride salts. Aside from the two ionic compounds originally present in the solutions, AgNO 3 and NaF, two additional ionic compounds may be derived from this collection of ions: NaNO 3 and AgF. One merely needs to identify all the ions present in the solution and then consider if possible cation/anion pairing could result in an insoluble compound.įor example, mixing solutions of silver nitrate and sodium fluoride will yield a solution containing Ag +, NO 3 −, Na +, and F − ions. The solubility table in Table 1 may be used to predict whether a precipitation reaction will occur when solutions of soluble ionic compounds are mixed together. A precipitate of PbI2 forms when solutions containing Pb2+ and I− are mixed. The properties of pure PbI 2 crystals make them useful for fabrication of X-ray and gamma ray detectors. Lead iodide is a bright yellow solid that was formerly used as an artist’s pigment known as iodine yellow ( Figure 1). Solubilities of Common Ionic Compounds in WaterĪ vivid example of precipitation is observed when solutions of potassium iodide and lead nitrate are mixed, resulting in the formation of solid lead iodide: For purposes of predicting the identities of solids formed by precipitation reactions, one may simply refer to patterns of solubility that have been observed for many ionic compounds ( Table 1). More information on these important concepts is provided in the text chapter on solutions. Substances with relatively low solubilities are said to be insoluble, and these are the substances that readily precipitate from solution. A substance will precipitate when solution conditions are such that its concentration exceeds its solubility. Substances with relatively large solubilities are said to be soluble. The extent to which a substance may be dissolved in water, or any solvent, is quantitatively expressed as its solubility, defined as the maximum concentration of a substance that can be achieved under specified conditions. Precipitation reactions also play a central role in many chemical analysis techniques, including spot tests used to identify metal ions and gravimetric methods for determining the composition of matter (see the last module of this chapter).
They are used widely in industry for production of a number of commodity and specialty chemicals. These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as double displacement, double replacement, or metathesis reactions. Precipitation Reactions and Solubility RulesĪ precipitation reaction is one in which dissolved substances react to form one (or more) solid products. The following sections of this chapter (section 6.2-6.4) will provide an introduction to three of the most prevalent types of chemical reactions: precipitation, acid-base, and oxidation-reduction.
Faced with a wide range of varied interactions between chemical substances, scientists have likewise found it convenient (or even necessary) to classify chemical interactions by identifying common patterns of reactivity. When they exchange blows with their fists or feet, we say they are fighting. When two humans exchange information, we say they are communicating. Humans interact with one another in various and complex ways, and we classify these interactions according to common patterns of behavior. Predict the solubility of common inorganic compounds by using solubility rules.Recognize and identify examples of precipitation reactions.By the end of this section, you will be able to:
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