Single And Double Displacement Reactions

Learning Objectives

Recognize chemic reactions equally single-replacement reactions and double-replacement reactions.
Utilize the periodic table, an activity series, or solubility rules to predict whether unmarried-replacement reactions or double-replacement reactions will occur.

Upward to at present, nosotros take presented chemical reactions every bit a topic, but we have not discussed how the products of a chemical reaction tin can be predicted. Here nosotros will begin our study of certain types of chemic reactions that allow us to predict what the products of the reaction will exist.

A single-replacement reaction is a chemic reaction in which one element is substituted for another element in a compound, generating a new chemical element and a new chemical compound every bit products. For example,

2 HCl(aq) + Zn(s) → ZnCl₂(aq) + H₂(1000)

is an example of a single-replacement reaction. The hydrogen atoms in HCl are replaced by Zn atoms, and in the process a new element—hydrogen—is formed. Some other instance of a unmarried-replacement reaction is

2 NaCl(aq) + F₂(thou) → 2 NaF(due south) + Cl₂(g)

Hither the negatively charged ion changes from chloride to fluoride. A typical feature of a single-replacement reaction is that at that place is one element every bit a reactant and some other element as a production.

Non all proposed single-replacement reactions will occur between two given reactants. This is most easily demonstrated with fluorine, chlorine, bromine, and iodine. Collectively, these elements are called the halogens and are in the next-to-terminal column on the periodic table (run across Effigy 4.1 "Halogens on the Periodic Table"). The elements on top of the cavalcade will supervene upon the elements beneath them on the periodic table just not the other way around. Thus, the reaction represented past

CaI_two(s) + Cl₂(g) → CaCl₂(south) + I₂(s)

volition occur, just the reaction

CaF₂(s) + Br₂(ℓ) → CaBr₂(south) + F_ii(g)

will not because bromine is below fluorine on the periodic tabular array. This is merely one of many ways the periodic table helps us empathise chemistry.

Figure 4.1 Halogens on the Periodic Tabular array

Halogens

The halogens are the elements in the next-to-concluding column on the periodic tabular array.

Case 2

Will a unmarried-replacement reaction occur? If and so, place the products.

MgCl_two + I₂ → ?
CaBr₂ + F₂ → ?

Solution

Because iodine is beneath chlorine on the periodic table, a single-replacement reaction will not occur.
Because fluorine is higher up bromine on the periodic table, a single-replacement reaction will occur, and the products of the reaction volition exist CaF_ii and Br₂.

Test Yourself

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

FeI₂ + Cl₂ → ?

Answer

Yes; FeCl₂ and I₂

Chemical reactivity trends are easy to predict when replacing anions in unproblematic ionic compounds—merely utilise their relative positions on the periodic tabular array. However, when replacing the cations, the trends are not as straightforward. This is partly because there are and then many elements that can form cations; an chemical element in one cavalcade on the periodic tabular array may supercede another element nearby, or it may non. A list called the activity series does the same thing the periodic table does for halogens: information technology lists the elements that will replace elements below them in unmarried-replacement reactions. A simple activity series is shown below.

Activity Series for Cation Replacement in Single-Replacement Reactions

Li
K
Ba
Sr
Ca
Na
Mg
Al
Mn
Zn
Cr
Iron
Ni
Sn
Pb
H_two
Cu
Hg
Ag
Pd
Pt
Au

Using the activity serial is similar to using the positions of the halogens on the periodic table. An element on top will replace an element beneath it in compounds undergoing a single-replacement reaction. Elements will non supervene upon elements above them in compounds.

Example three

Use the activeness serial to predict the products, if whatever, of each equation.

FeCl₂ + Zn → ?
HNO₃ + Au → ?

Solution

Considering zinc is in a higher place atomic number 26 in the activity series, it volition supersede iron in the chemical compound. The products of this single-replacement reaction are ZnCl₂ and Iron.
Golden is beneath hydrogen in the activeness series. Equally such, it will not replace hydrogen in a chemical compound with the nitrate ion. No reaction is predicted.

Exam Yourself

Use the action serial to predict the products, if any, of this equation.

AlPO₄ + Mg → ?

Answer

Mg_iii(PO₄)_ii and Al

A double-replacement reaction occurs when parts of 2 ionic compounds are exchanged, making 2 new compounds. A feature of a double-replacement equation is that there are ii compounds as reactants and two different compounds as products. An example is

CuCl_ii(aq) + two AgNO₃(aq) → Cu(NO_three)₂(aq) + 2 AgCl(south)

There are ii equivalent means of considering a double-replacement equation: either the cations are swapped, or the anions are swapped. (You cannot swap both; y'all would stop upward with the same substances you lot started with.) Either perspective should allow yous to predict the proper products, as long every bit yous pair a cation with an anion and not a cation with a cation or an anion with an anion.

Instance iv

Predict the products of this double-replacement equation: BaCl_two + Na₂SO_four → ?

Solution

Thinking about the reaction as either switching the cations or switching the anions, we would expect the products to be BaSO_iv and NaCl.

Test Yourself

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

Answer

KNO_three and AgBr

Predicting whether a double-replacement reaction occurs is somewhat more difficult than predicting a single-replacement reaction. However, at that place is 1 blazon of double-replacement reaction that we tin predict: the precipitation reaction. A atmospheric precipitation reaction occurs when two ionic compounds are dissolved in water and form a new ionic compound that does non deliquesce; this new compound falls out of solution as a solid precipitate. The germination of a solid precipitate is the driving force that makes the reaction proceed.

To guess whether double-replacement reactions will occur, we demand to know what kinds of ionic compounds form precipitates. For this, nosotros use solubility rules, which are general statements that predict which ionic compounds dissolve (are soluble) and which do not (are not soluble or insoluble). Tabular array 4.1 "Some Useful Solubility Rules" lists some full general solubility rules. We demand to consider each ionic compound (both the reactants and the possible products) in light of the solubility rules in Table 4.1 "Some Useful Solubility Rules". If a compound is soluble, we utilize the (aq) label with information technology, indicating information technology dissolves. If a compound is not soluble, we use the (s) label with information technology and presume that it will precipitate out of solution. If everything is soluble, so no reaction volition be expected.

Table 4.1 Some Useful Solubility Rules

These compounds by and large dissolve in h2o (are soluble):	Exceptions:
All compounds of Li⁺, Na⁺, M⁺, Rb⁺, Cs⁺, and NH₄ ⁺	None
All compounds of NO₃ ⁻ and C_twoH_iiiO₂ ⁻	None
Compounds of Cl⁻, Br⁻, I⁻	Ag⁺, Hg₂ ⁱⁱ⁺, Pb^two+
Compounds of SO₄ ²	Hg₂ ²⁺, Pb^two+, Sr^two+, Ba²⁺
These compounds by and large do non dissolve in h2o (are insoluble):	Exceptions:
Compounds of CO₃ ²⁻ and PO₄ ³⁻	Compounds of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and NH₄ ⁺
Compounds of OH⁻	Compounds of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺, Sr²⁺, and Baⁱⁱ⁺

For example, consider the possible double-replacement reaction between Na₂SO₄ and SrCl₂. The solubility rules say that all ionic sodium compounds are soluble and all ionic chloride compounds are soluble except for Ag⁺, Hg₂ ^two+, and Pb²⁺, which are non being considered here. Therefore, Na_twoSO₄ and SrCl_two are both soluble. The possible double-replacement reaction products are NaCl and SrSO₄. Are these soluble? NaCl is (past the same dominion nosotros only quoted), merely what nearly SrSO₄? Compounds of the sulfate ion are generally soluble, but Srⁱⁱ⁺ is an exception: nosotros expect it to be insoluble—a precipitate. Therefore, we await a reaction to occur, and the balanced chemical equation would be

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

Yous would expect to see a visual modify corresponding to SrSO₄ precipitating out of solution (Effigy iv.2 "Double-Replacement Reactions").

Effigy 4.2 Double-Replacement Reactions

Double Replacement Reaction

Some double-replacement reactions are obvious because you can see a solid precipitate coming out of solution.

Example 5

Volition a double-replacement reaction occur? If then, identify the products.

Ca(NO_iii)₂ + KBr → ?
NaOH + FeCl₂ → ?

Solution

According to the solubility rules, both Ca(NO₃)_two and KBr are soluble. Now we consider what the double-replacement products would exist by switching the cations (or the anions)—namely, CaBr_two and KNO₃. However, the solubility rules predict that these two substances would also exist soluble, so no precipitate would form. Thus, we predict no reaction in this case.
Co-ordinate to the solubility rules, both NaOH and FeCl₂ are expected to be soluble. If we assume that a double-replacement reaction may occur, we need to consider the possible products, which would be NaCl and Fe(OH)₂. NaCl is soluble, but, according to the solubility rules, Fe(OH)₂ is not. Therefore, a reaction would occur, and Fe(OH)₂(s) would precipitate out of solution. The counterbalanced chemical equation is

2NaOH(aq) + FeCl₂(aq) → 2NaCl(aq) + Atomic number 26(OH)_two(s)

Exam Yourself

Will a double-replacement equation occur? If so, identify the products.

Sr(NO_three)_ii + KCl → ?

Respond

No reaction; all possible products are soluble.

Key Takeaways

A single-replacement reaction replaces 1 element for some other in a compound.
The periodic tabular array or an activity serial tin help predict whether single-replacement reactions occur.
A double-replacement reaction exchanges the cations (or the anions) of two ionic compounds.
A precipitation reaction is a double-replacement reaction in which one production is a solid precipitate.
Solubility rules are used to predict whether some double-replacement reactions volition occur.

Exercises

What are the general characteristics that help you recognize single-replacement reactions?

What are the general characteristics that assistance yous recognize double-replacement reactions?

Assuming that each single-replacement reaction occurs, predict the products and write each counterbalanced chemic equation.

a) Zn + Fe(NO₃)_two → ?

b) F_two + FeI₃ → ?

4. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.

a) Li + MgSO₄ → ?

b) NaBr + Cl_two → ?

five. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.

a) Sn + H₂SO₄ → ?

b) Al + NiBr₂ → ?

six. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemic equation.

a) Mg + HCl → ?

b) Howdy + Br₂ → ?

7. Use the periodic tabular array or the activity serial to predict if each single-replacement reaction volition occur and, if so, write a balanced chemical equation.

a) FeCl_two + Br_two → ?

b) Iron(NO₃)_iii + Al → ?

8. Employ the periodic table or the activeness series to predict if each unmarried-replacement reaction will occur and, if so, write a counterbalanced chemical equation.

a) Zn + Fe₃(PO_iv)_ii → ?

b) Ag + HNO₃ → ?

9. Use the periodic table or the action series to predict if each single-replacement reaction volition occur and, if then, write a balanced chemical equation.

a) NaI + Cl₂ → ?

b) AgCl + Au → ?

10. Use the periodic table or the activity series to predict if each single-replacement reaction will occur and, if so, write a counterbalanced chemical equation.

a) Pt + H₃PO₄ → ?

b) Li + H_iiO → ? (Hint: treat H₂O as if it were composed of H⁺ and OH⁻ ions.)

11. Assuming that each double-replacement reaction occurs, predict the products and write each counterbalanced chemic equation.

a) Zn(NO₃)_two + NaOH → ?

b) HCl + Na₂S → ?

12. Bold that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.

a) Ca(C_twoH₃O₂)_two + HNO₃ → ?

b) Na_twoCO₃ + Sr(NO_ii)₂ → ?

13. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.

a) Pb(NO_iii)_ii + KBr → ?

b) Chiliad_twoO + MgCO_three → ?

fourteen. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.

a) Sn(OH)₂ + FeBr₃ → ?

b) CsNO_iii + KCl → ?

15. Apply the solubility rules to predict if each double-replacement reaction volition occur and, if so, write a balanced chemic equation.

a) Lead(NO_iii)₂ + KBr → ?

b) K₂O + Na_twoCO₃ → ?

16. Utilize the solubility rules to predict if each double-replacement reaction will occur and, if so, write a balanced chemical equation.

a) Na_twoCO₃ + Sr(NO₂)₂ → ?

b) (NH₄)_twoAnd so₄ + Ba(NO_three)₂ → ?

17. Utilise the solubility rules to predict if each double-replacement reaction volition occur and, if and then, write a balanced chemical equation.

a) M₃PO₄ + SrCl₂ → ?

b) NaOH + MgCl₂ → ?

18. Apply the solubility rules to predict if each double-replacement reaction will occur and, if then, write a balanced chemic equation.

a) KC_iiH₃O₂ + Li_twoCO₃ → ?

b) KOH + AgNO_three → ?

Answers

one.One element replaces another element in a compound.

a) Zn + Iron(NO_iii)₂ → Zn(NO₃)₂ + Atomic number 26

b) 3 F₂ + 2 FeI₃ → iii I₂ + 2 FeF_iii 5.

a) Sn + H₂SO₄ → SnSO_iv + H₂

b) 2 Al + 3 NiBr₂ → ii AlBr_iii + iii Ni

a) No reaction occurs.

b) Iron(NO₃)₃ + Al → Al(NO_iii)₃ + Fe

a) 2 NaI + Cl_ii → 2 NaCl + I₂

b) No reaction occurs.

xi.

a) Zn(NO₃)_ii + ii NaOH → Zn(OH)_two + two NaNO₃

b) 2 HCl + Na_twoS → 2 NaCl + H₂Due south

13.

a) Pb(NO_three)₂ + 2 KBr → PbBr₂ + 2 KNO₃

b) K₂O + MgCO₃ → K_twoCO_three + MgO

xv.

a) Atomic number 82(NO₃)_two + two KBr → PbBr₂(s) + two KNO₃

b) No reaction occurs.

17.

a) two Thou₃PO_iv + 3 SrCl_ii → Sr₃(PO₄)₂(s) + 6 KCl

b) ii NaOH + MgCl_two → 2 NaCl + Mg(OH)₂(south)