Precipitates double displacement reactions

Copper(n) sulfate, CUSO4, reacts with sodium hydroxide, NaOH, in a double displacement reaction. A precipitate of copper(n) hydroxide, Cu(OH)2, and aqueous sodium sulfate, Na2S04, is produced. 

In Chapter 9, as in most of Unit 4, you learned about equilibrium reactions. In this section, you analyzed precipitation reactions. You mainly examined double-displacement reactions—reactions in which two soluble ionic compounds react to form a precipitate. You used the solubility product constant, Ksp, to predict whether or not a precipitate would form for given concentrations of ions. In Unit 5, you will learn about a class of reactions that will probably be new to you. You will see how these reactions interconvert chemical and electrical energy. 

Many double displacement reactions occur between ionic compounds that are dissolved in water. Sometimes one of the products of a double displacement reaction will come out of solution, usually as a gas or a precipitate. Solutions are mixtures of two or more substances, called the solutes, dissolved in another substance, the solvent. For example, salt water is a solution. The salt is the solute and the water is the solvent. In a solution, it is impossible to see the separate parts. But if two chemicals that are dissolved in water... 

Figure 4.2 The mixing of a silver sulfate solution with an aluminum chloride solution, results in the formation of aqueous aluminum sulfate and the precipitation of silver chloride. This is an example of a double displacement reaction.

In the example of a double displacement reaction below, a silver sulfate (Ag2S04) solution is mixed with an aluminum chloride (AlCl3) solution. One of the products, silver chloride (AgCl), precipitates out of the solution as a solid. The (s) following the formula for silver chloride shows that it is a solid. 

When a precipitate was formed in Activity 9.1, the reaction that occurred was a double displacement reaction. Each reactant contained two ions. When two reactants combined, a precipitate formed if two of the ions present were more stable and if they bonded to form a low solubility solid. An ionic equation for such a reaction is Ag+ (aq) + N03-(aq) + K+ (aq) + CL (aq) -> K+ (aq) + N03-(aq) + AgCl(s). The net ionic equation is Ag+ (aq) + Or (aq) — AgCl(s). Potassium and chloride ions are called spectator ions. They only watch the reaction. 

Double Displacement Reactions that Form a Precipitate... 

A precipitate is a solid that separates from a solution as the result of a chemical reaction. You will learn more about precipitates in Chapter 9. Many double displacement reactions involve the formation of a precipitate. 

Examine the double displacement reaction that occurs when aqueous solutions of barium chloride and potassium sulfate are mixed. A white precipitate is immediately formed. The equation for the reaction is BaCl2(aq) + K2S04(aq) —> BaSChfs) + 2KCl(aq)... 

How do you know that the precipitate is BaS04 and not KC1 More generally, how can you predict whether a precipitate will be formed in a double displacement reaction In this chapter, you will be given information on solubility as you need it. You will learn more about how to predict whether a compound is soluble or not in Chapter 9. Barium sulfate, BaS04 is not soluble in water, while potassium chloride, KC1, is. Therefore, a reaction will take place and barium sulfate will be the precipitate. 

In summary, to determine the products and their physical states in a double displacement reaction, you must first deconstruct the reactants. Then switch the cations, and reconstruct the products using proper chemical formulas. You should then balance the chemical equation. You will be given information to determine which of the products, if any, will form a precipitate. Finally, you can write the physical state—(s) or (aq)— of each product and balance the equation. 

What happens if both products are soluble ionic compounds Both ionic compounds will be ions dissolved in the water. If neither product precipitates out, no reaction occurs. Try the following problem to practise writing the products of double displacement reactions and predicting their states. 

Most often, double displacement reactions result in the formation of a precipitate. However, some double displacement reactions result in the formation of an unstable compound which then decomposes to water and a gas. 

How would you determine the percentage yield of a double displacement reaction that produces a precipitate Consider this question to prepare for your Chemistry Course Challenge. 

You will need to use the following double displacement reaction. This reaction produces a precipitate of barium sulfate. 

When you mix two aqueous ionic compounds together, there are two possible outcomes. Either the compounds will remain in solution without reacting, or one aqueous ionic compound will chemically react with the other. How can you predict which outcome will occur Figure 9.4 shows what happens when an aqueous solution of lead(II) nitrate is added to an aqueous solution of potassium iodide. As you can see, a yellow solid—a precipitate—is forming. This is a double displacement reaction. Recall, from Chapter 4, that a double displacement reaction is a chemical reaction that involves the exchange of ions to form two new compounds. It has the general equation... 

Lead(ll) nitrate and potassium iodide are clear, colourless aqueous solutions. Mixing them causes a double displacement reaction. An insoluble yellow precipitate (lead(ll) iodide) and a soluble salt (potassium nitrate) are produced. 

A double displacement reaction occurs in aqueous solution when magnesium phosphate reacts with lead(II) nitrate. If 20.0 mL of 0.750 mol/L magnesium phosphate reacts, what is the maximum mass of precipitate that can be formed ... 

Write the molecular equation. The molecular equation shows the reactants and products as molecules. The solubility rules are used to determine if a product is insoluble. Precipitation reactions are examples of a double-displacement reaction. Therefore, the cation of... 

Figure 13 shows the result of the reaction between KI and Pb(N03)2- The products are a yellow precipitate of Pbl2 and a colorless solution of KNO3. From the equation, it appears as though the parts of the compounds just change places. Early chemists called this a double-displacement reaction. It occurs when two compounds in aqueous solution appear to exchange ions and form two new compounds. For this to happen, one of the products must be a solid precipitate, a gas, or a molecular compound, such as water. Water is often written as HOH in these equations. 

Write a balanced equation for the reaction. What is the precipitate Write its empirical formula. (Hint It was a double-displacement reaction.)... 

Review the "Stoichiometry chapter for information about mass-mass stoichiometry. In this investigation, you will use a double-displacement reaction, but Na2C03 will be used as a reagent to identify how much calcium is present in a sample. Like strontium and other Group 2 metals, calcium salts react with carbonate-containing salts to produce an insoluble precipitate. 

We can solve the city s problem by doing some careful gravimetric analysis, because calcium salts and carbonate compounds undergo double-displacement reactions to 3deld insoluble calcium carbonate as a precipitate. 

Let s suppose we were to carry out a chemical reaction between aqueous solutions of lead (II) chlorate and sodium iodide. We mix the two solutions in a test tube, and we find that a solid precipitate forms and falls to the bottom of the test tube. We would want to be able to identify what the solid was. The first thing that we might want to do is make a word equation for the reaction that we think is taking place. Treating this as a double displacement reaction, we would get the word equation shown here ... 

In double-displacement reactions, the positive portions of two ionic compounds are interchanged. For a double-displacement reaction to take place, at least one of the products must be a precipitate or water. An example of a double-displacement reaction is shown in Figure 6.11. 

When clear aqueous solutions of lead(II) nitrate and potassium iodide are mixed, a double-displacement reaction takes place and a yellow solid appears in the mixture. This solid is lead(II) iodide, and it precipitates out because it is insoluble in water, unlike the two reactants and the other product. 

Precipitation reactions, such as the ones we will see in this section, belong to a general class of reactions called double-displacement reactions. (Double displacement reactions are also called double-replacement, double-exchange, or metathesis reactions.) Double displacement reactions have the following form, signifying that the elements in two reacting compounds change partners. 

Sometimes a double-displacement reaction has one produa that is insoluble in water. As that produa forms, it emerges, or precipitates, from the solution as a solid. This process is called precipitation, such a reaaion is called a precipitation reaction, and the solid is called the precipitate. For example, when water solutions of calcium nitrate and sodium carbonate are mixed, calcium carbonate precipitates from the solution while the other product, sodium nitrate, remains dissolved. 

In order to predict whether a precipitation reaction will take place when two aqueous ionic compounds are mixed, you need to be able to predict whether the possible products of the double-displacement reaction are soluble or insoluble in water. 

As you can see, acid-base reactions, like precipitation reactions, are metathesis (double-displacement) reactions. The molecular equation for the reaction of aluminum hydroxide, the active ingredient in some antacid tablets, with HCl, the major component of stomach acid, shows this clearly ... 

Double-displacement reactions can be further classified as precipitation, gas formation, and acid-base neutralization reactions. 

So we can classify a reaction such as this one as a precipitation reaction or as a double-displacement reaction. Either name is correct, but precipitation is more commonly used by chemists. 

A precipitation reaction is also called a double-displacement reaction. 

O Why are precipitation reactions also called double displacement reactions ... 

Spectator ions are ions that remain in solution during a precipitation/double-displacement reaction. For example, in the reaction BaCl2(a[Pg.671]

The preceding reaction is an example of a metathesis reaction (also called a double-displacement reaction), a reaction that involves the exchange of parts between the two compounds. (In this case, the cations in the two compounds exchange anions, so Pb ends up with F as PW2 and ends up with N03 as KNO3.) As we will see, the precipitation reactions discussed in this chapter are examples of metathesis reactions. 

In single displacement reactions, 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 t3 e occur in a solution, and either an insoluble solid (precipitation reactions) or water (neutralization reactions) will be formed. 

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

A double-displacement reaction results from pouring a clear, colorless solution of Pb(N03)2 into a clear, colorless solution of Kl, forming a yellow precipitate of Pblj. 

Ray ran a double-displacement reaction using 0.050 mol CuCl2 and 0.10 mol AgNOs. The resulting white precipitate was removed by filtration. The filtrate was accidentally left open on the lab bench for over a week, and when Ray returned the flask contained solid, blue crystals. Ray weighed the crystals and found they had a mass of 14.775 g. Was Ray expecting this number If not, what did he expect ... 

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