Learning Objectives

Recognize chemistry reactions together single-replacement reactions and also double-replacement reactions.Use the routine table, an activity series, or solubility rules to predict whether single-replacement reactions or double-replacement reactions will certainly occur.

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Up come now, we have presented chemistry reactions as a topic, but we have not debated how the commodities of a chemistry reaction have the right to be predicted. Here we will begin our examine of certain species of chemistry reactions that permit us to predict what the commodities of the reaction will be.

A single-replacement reaction is a chemistry reaction in which one aspect is substituted for another element in a compound, generating a new element and also a brand-new compound as products. Because that example,

2 HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)

is an example of a single-replacement reaction. The hydrogen atoms in HCl are changed by Zn atoms, and in the process a brand-new element—hydrogen—is formed. Another example the a single-replacement reaction is

2 NaCl(aq) + F2(g) → 2 NaF(s) + Cl2(g)

Here the negatively fee ion alters from chloride come fluoride. A usual characteristic the a single-replacement reaction is that there is one aspect as a reactant and also another aspect as a product.

Not every proposed single-replacement reactions will certainly occur in between two provided reactants. This is most easily demonstrated through fluorine, chlorine, bromine, and also iodine. Collectively, these facets are referred to as the halogens and also are in the next-to-last pillar on the periodic table (see figure 4.1 “Halogens top top the regular Table”). The aspects on top of the column will replace the aspects below lock on the routine table however not the other method around. Thus, the reaction stood for by

CaI2(s) + Cl2(g) → CaCl2(s) + I2(s)

will occur, but the reaction

CaF2(s) + Br2(ℓ) → CaBr2(s) + F2(g)

will not since bromine is listed below fluorine on the periodic table. This is simply one of numerous ways the routine table help us know chemistry.

Figure 4.1 Halogens on the regular Table


The halogens are the facets in the next-to-last pillar on the routine table.

Example 2

Will a single-replacement reaction occur? If so, determine the products.

MgCl2 + I2 → ?CaBr2 + F2 → ?


Because iodine is listed below chlorine ~ above the regular table, a single-replacement reaction will not occur.Because fluorine is above bromine ~ above the regular table, a single-replacement reaction will occur, and the commodities of the reaction will be CaF2 and also Br2.

Test Yourself

Will a single-replacement reaction occur? If so, identify the products.

FeI2 + Cl2 → ?


Yes; FeCl2 and also I2

Chemical reactivity trends are straightforward to predict as soon as replacing anions in straightforward ionic compounds—simply usage their relative positions ~ above the periodic table. However, when replacing the cations, the trends are not together straightforward. This is partly because there space so many facets that can kind cations; an facet in one obelisk on the routine table may replace another element nearby, or it might not. A list dubbed the task series does the exact same thing the periodic table does because that halogens: it lists the facets that will replace facets below lock in single-replacement reactions. A basic activity collection is shown below.

Activity series for Cation instead of in Single-Replacement Reactions


Using the activity collection is comparable to using the location of the halogens top top the periodic table. An element on top will replace an element below it in compounds undergoing a single-replacement reaction. Facets will not replace elements over them in compounds.

Example 3

Use the activity collection to guess the products, if any, of every equation.

FeCl2 + Zn → ?HNO3 + Au → ?


Because zinc is over iron in the activity series, it will replace iron in the compound. The assets of this single-replacement reaction are ZnCl2 and also Fe.Gold is listed below hydrogen in the task series. As such, it will not change hydrogen in a compound through the nitrate ion. No reaction is predicted.

Test Yourself

Use the activity series to suspect the products, if any, of this equation.

AlPO4 + Mg → ?


Mg3(PO4)2 and also Al

A double-replacement reaction occurs once parts of 2 ionic compounds are exchanged, do two new compounds. A characteristic of a double-replacement equation is that there space two compounds as reactants and also two different compounds together products. An instance is

CuCl2(aq) + 2 AgNO3(aq) → Cu(NO3)2(aq) + 2 AgCl(s)

There are two identical ways that considering a double-replacement equation: one of two people the cations space swapped, or the anions room swapped. (You cannot swap both; you would end up through the exact same substances you started with.) one of two people perspective should permit you come predict the ideal products, as lengthy as girlfriend pair a cation v an anion and also not a cation with a cation or an anion v an anion.

Example 4

Predict the assets of this double-replacement equation: BaCl2 + Na2SO4 → ?


Thinking around the reaction together either switching the cations or convert the anions, us would expect the assets to it is in BaSO4 and NaCl.

Test Yourself

Predict the products of this double-replacement equation: KBr + AgNO3 → ?


KNO3 and AgBr

Predicting whether a double-replacement reaction wake up is rather more challenging than predicting a single-replacement reaction. However, there is one type of double-replacement reaction the we deserve to predict: the precipitation reaction. A precipitation reaction occurs as soon as two ionic link are liquified in water and type a brand-new ionic compound the does not dissolve; this brand-new compound falls out of equipment as a solid precipitate. The formation of a solid precipitate is the driving pressure that renders the reaction proceed.

To judge whether double-replacement reactions will certainly occur, we need to know what kinds of ionic compounds form precipitates. For this, we use solubility rules, i m sorry are basic statements that predict i m sorry ionic compounds dissolve (are soluble) and also which carry out not (are no soluble or insoluble). Table 4.1 “Some useful Solubility Rules” perform some general solubility rules. We need to take into consideration each ionic compound (both the reactants and also the possible products) in light of the solubility rule in Table 4.1 “Some useful Solubility Rules”. If a link is soluble, we use the (aq) label with it, indicating it dissolves. If a link is no soluble, we usage the (s) label with it and also assume that it will precipitate out of solution. If whatever is soluble, then no reaction will be expected.

Table 4.1 Some beneficial Solubility Rules

These compounds normally dissolve in water (are soluble):Exceptions:
All compounds of Li+, Na+, K+, Rb+, Cs+, and NH4+None
All compound of NO3− and C2H3O2−None
Compounds of Cl−, Br−, I−Ag+, Hg22+, Pb2+
Compounds the SO42Hg22+, Pb2+, Sr2+, Ba2+
These compounds usually do not dissolve in water (are insoluble):Exceptions:
Compounds that CO32− and also PO43−Compounds the Li+, Na+, K+, Rb+, Cs+, and also NH4+
Compounds of OH−Compounds the Li+, Na+, K+, Rb+, Cs+, NH4+, Sr2+, and also Ba2+

For example, consider the feasible double-replacement reaction in between Na2SO4 and SrCl2. The solubility rules say the all ionic salt compounds space soluble and also all ionic chloride compounds room soluble other than for Ag+, Hg22+, and Pb2+, which are not being considered here. Therefore, Na2SO4 and SrCl2 are both soluble. The possible double-replacement reaction commodities are NaCl and SrSO4. Are these soluble? NaCl is (by the same ascendancy we simply quoted), however what about SrSO4? compound of the sulfate ion are normally soluble, but Sr2+ is one exception: we expect it to be insoluble—a precipitate. Therefore, we suppose a reaction to occur, and the balanced chemical equation would be

Na2SO4(aq) + SrCl2(aq) → 2 NaCl(aq) + SrSO4(s)

You would mean to view a visual change corresponding to SrSO4 precipitating the end of systems (Figure 4.2 “Double-Replacement Reactions”).

Figure 4.2 Double-Replacement Reactions


Some double-replacement reaction are noticeable because you have the right to see a hard precipitate coming the end of solution.

Source: picture courtesy of Choij, http://commons.wikimedia.org/wiki/File:Copper_solution.jpg.

Example 5

Will a double-replacement reaction occur? If so, recognize the products.

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Ca(NO3)2 + KBr → ?NaOH + FeCl2 → ?


According come the solubility rules, both Ca(NO3)2 and KBr space soluble. Now we think about what the double-replacement assets would be by switching the cations (or the anions)—namely, CaBr2 and KNO3. However, the solubility rule predict the these 2 substances would also be soluble, for this reason no precipitate would form. Thus, us predict no reaction in this case.

According to the solubility rules, both NaOH and also FeCl2 space expected to it is in soluble. If us assume the a double-replacement reaction might occur, we need to take into consideration the possible products, which would be NaCl and Fe(OH)2. NaCl is soluble, but, follow to the solubility rules, Fe(OH)2 is not. Therefore, a reaction would certainly occur, and also Fe(OH)2(s) would certainly precipitate the end of solution. The well balanced chemical equation is