Single Replacement Reaction General Formula

Learning Objectives

Recognize chemical reactions equally single-replacement reactions and double-replacement reactions.
Use the periodic tabular array, an activity series, or solubility rules to predict whether unmarried-replacement reactions or double-replacement reactions volition occur.

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

A unmarried-replacement reaction is a chemic reaction in which ane chemical element is substituted for another element in a compound, generating a new chemical element and a new compound equally products. For example,

2 HCl(aq) + Zn(south) → ZnCl_two(aq) + H₂(g)

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

ii NaCl(aq) + F₂(one thousand) → 2 NaF(s) + Cl_ii(g)

Here the negatively charged ion changes from chloride to fluoride. A typical characteristic of a single-replacement reaction is that there is one element equally a reactant and another element every bit a product.

Non all proposed unmarried-replacement reactions will occur between two given reactants. This is nearly hands demonstrated with fluorine, chlorine, bromine, and iodine. Collectively, these elements are called the halogens and are in the side by side-to-concluding column on the periodic table (meet Effigy 4.1 "Halogens on the Periodic Table"). The elements on tiptop of the column will supplant the elements below them on the periodic table simply not the other way around. Thus, the reaction represented by

CaI₂(due south) + Cl_two(g) → CaCl_two(due south) + I₂(southward)

volition occur, but the reaction

CaF₂(s) + Br₂(ℓ) → CaBr₂(s) + F_ii(chiliad)

will not because bromine is below fluorine on the periodic tabular array. This is simply one of many ways the periodic table helps united states understand chemistry.

Figure four.ane Halogens on the Periodic Table

Halogens

The halogens are the elements in the side by side-to-last column on the periodic tabular array.

Instance two

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

MgCl₂ + I₂ → ?
CaBr₂ + F_ii → ?

Solution

Because iodine is beneath chlorine on the periodic table, a single-replacement reaction will not occur.
Because fluorine is above bromine on the periodic table, a unmarried-replacement reaction will occur, and the products of the reaction will be CaF_ii and Br₂.

Test Yourself

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

FeI₂ + Cl_two → ?

Answer

Yes; FeCl₂ and I_ii

Chemical reactivity trends are easy to predict when replacing anions in simple ionic compounds—simply employ their relative positions on the periodic table. However, when replacing the cations, the trends are not as straightforward. This is partly considering there are and then many elements that tin class cations; an element in one column on the periodic table may replace another element nearby, or it may non. A list called the activity series does the same thing the periodic tabular array does for halogens: it lists the elements that will replace elements beneath them in single-replacement reactions. A unproblematic activity series is shown below.

Activity Series for Cation Replacement in Unmarried-Replacement Reactions

Li
K
Ba
Sr
Ca
Na
Mg
Al
Mn
Zn
Cr
Fe
Ni
Sn
Lead
H₂
Cu
Hg
Ag
Pd
Pt
Au

Using the activeness series is similar to using the positions of the halogens on the periodic tabular array. An element on elevation will replace an element below it in compounds undergoing a single-replacement reaction. Elements will not supplant elements above them in compounds.

Example 3

Use the action series to predict the products, if any, of each equation.

FeCl₂ + Zn → ?
HNO₃ + Au → ?

Solution

Because zinc is above iron in the activity series, it volition supersede atomic number 26 in the compound. The products of this single-replacement reaction are ZnCl_two and Fe.
Golden is below hydrogen in the activeness series. As such, it will not replace hydrogen in a chemical compound with the nitrate ion. No reaction is predicted.

Test Yourself

Utilise the activity serial to predict the products, if any, of this equation.

AlPO₄ + Mg → ?

Answer

Mg₃(PO₄)₂ and Al

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

CuCl₂(aq) + two AgNO_iii(aq) → Cu(NO_iii)₂(aq) + two AgCl(s)

There are 2 equivalent ways of considering a double-replacement equation: either the cations are swapped, or the anions are swapped. (You cannot swap both; you would end upwardly with the same substances you started with.) Either perspective should allow you to predict the proper products, as long as you pair a cation with an anion and not a cation with a cation or an anion with an anion.

Example 4

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

Solution

Thinking about the reaction every bit either switching the cations or switching the anions, we would wait the products to be BaSO_four and NaCl.

Examination Yourself

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

Answer

KNO₃ and AgBr

Predicting whether a double-replacement reaction occurs is somewhat more than hard than predicting a single-replacement reaction. However, there is 1 blazon of double-replacement reaction that nosotros can predict: the precipitation reaction. A atmospheric precipitation reaction occurs when ii ionic compounds are dissolved in water and form a new ionic compound that does not dissolve; this new compound falls out of solution every bit a solid precipitate. The formation of a solid precipitate is the driving forcefulness that makes the reaction keep.

To gauge whether double-replacement reactions will occur, we need to know what kinds of ionic compounds course 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). Table iv.1 "Some Useful Solubility Rules" lists some general solubility rules. Nosotros need to consider each ionic chemical compound (both the reactants and the possible products) in light of the solubility rules in Table 4.i "Some Useful Solubility Rules". If a compound is soluble, nosotros use the (aq) characterization with it, indicating it dissolves. If a compound is non soluble, nosotros use the (s) characterization with information technology and presume that it will precipitate out of solution. If everything is soluble, and then no reaction will be expected.

Table 4.one Some Useful Solubility Rules

These compounds mostly dissolve in water (are soluble):	Exceptions:
All compounds of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and NH_four ⁺	None
All compounds of NO₃ ⁻ and C_iiH_iiiO_ii ⁻	None
Compounds of Cl⁻, Br⁻, I⁻	Ag⁺, Hg₂ ^two+, Pb²⁺
Compounds of SO₄ ^two	Hg_ii ²⁺, Pb²⁺, Sr²⁺, Baⁱⁱ⁺
These compounds by and large do not deliquesce in water (are insoluble):	Exceptions:
Compounds of CO₃ ^two− and PO₄ ³⁻	Compounds of Li⁺, Na⁺, 1000⁺, Rb⁺, Cs⁺, and NH_iv ⁺
Compounds of OH⁻	Compounds of Li⁺, Na⁺, G⁺, Rb⁺, Cs⁺, NH₄ ⁺, Srⁱⁱ⁺, and Ba²⁺

For example, consider the possible double-replacement reaction between Na₂Then_iv and SrCl₂. The solubility rules say that all ionic sodium compounds are soluble and all ionic chloride compounds are soluble except for Ag⁺, Hg₂ ²⁺, and Pb²⁺, which are not existence considered here. Therefore, Na₂SO_iv and SrCl_two are both soluble. The possible double-replacement reaction products are NaCl and SrSO_four. Are these soluble? NaCl is (past the same rule we merely quoted), but what about SrSO₄? Compounds of the sulfate ion are more often than not soluble, merely Srⁱⁱ⁺ is an exception: we wait it to exist insoluble—a precipitate. Therefore, we expect a reaction to occur, and the counterbalanced chemical equation would be

Na_iiSO₄(aq) + SrCl₂(aq) → 2 NaCl(aq) + SrSO₄(southward)

You would expect to come across a visual alter corresponding to SrSO₄ precipitating out of solution (Figure four.2 "Double-Replacement Reactions").

Effigy 4.2 Double-Replacement Reactions

Double Replacement Reaction

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

Example v

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

Ca(NO₃)₂ + KBr → ?
NaOH + FeCl_ii → ?

Solution

Co-ordinate to the solubility rules, both Ca(NO₃)₂ and KBr are soluble. At present we consider what the double-replacement products would be past switching the cations (or the anions)—namely, CaBr₂ and KNO₃. However, the solubility rules predict that these two substances would also exist soluble, and then no precipitate would grade. Thus, we predict no reaction in this example.
According to the solubility rules, both NaOH and FeCl_ii are expected to be soluble. If nosotros assume that a double-replacement reaction may occur, nosotros need to consider the possible products, which would be NaCl and Iron(OH)₂. NaCl is soluble, but, according to the solubility rules, Iron(OH)₂ is not. Therefore, a reaction would occur, and Fe(OH)₂(s) would precipitate out of solution. The balanced chemical equation is

2NaOH(aq) + FeCl₂(aq) → 2NaCl(aq) + Fe(OH)₂(s)

Test Yourself

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

Sr(NO₃)₂ + KCl → ?

Reply

No reaction; all possible products are soluble.

Key Takeaways

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

Exercises

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

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

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

a) Zn + Fe(NO₃)_ii → ?

b) F₂ + 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 → ?

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

a) Sn + H₂Then_iv → ?

b) Al + NiBr_ii → ?

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

a) Mg + HCl → ?

b) Hi + Br_ii → ?

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

a) FeCl_two + Br₂ → ?

b) Iron(NO_iii)₃ + Al → ?

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

a) Zn + Fe_three(PO₄)₂ → ?

b) Ag + HNO₃ → ?

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

a) NaI + Cl₂ → ?

b) AgCl + Au → ?

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

a) Pt + H₃PO_iv → ?

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

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

a) Zn(NO₃)₂ + NaOH → ?

b) HCl + Na_twoS → ?

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

a) Ca(C₂H₃O_two)_two + HNO₃ → ?

b) Na₂CO₃ + Sr(NO_two)₂ → ?

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

a) Atomic number 82(NO_three)_two + KBr → ?

b) K₂O + MgCO₃ → ?

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

a) Sn(OH)_ii + FeBr₃ → ?

b) CsNO₃ + KCl → ?

15. Use the solubility rules to predict if each double-replacement reaction will occur and, if and then, write a balanced chemical equation.

a) Atomic number 82(NO_iii)_ii + KBr → ?

b) M₂O + Na₂CO₃ → ?

16. Use the solubility rules to predict if each double-replacement reaction will occur and, if and then, write a counterbalanced chemical equation.

a) Na_iiCO_three + Sr(NO₂)_ii → ?

b) (NH₄)₂Then₄ + Ba(NO₃)_two → ?

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

a) Grand₃PO_four + SrCl_ii → ?

b) NaOH + MgCl₂ → ?

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

a) KC₂H₃O_ii + Li₂CO₃ → ?

b) KOH + AgNO₃ → ?

Answers

ane.One chemical element replaces another element in a compound.

a) Zn + Fe(NO₃)₂ → Zn(NO₃)_two + Fe

b) iii F_ii + 2 FeI₃ → 3 I₂ + 2 FeF_three v.

a) Sn + H₂So_four → SnSO_four + H_ii

b) 2 Al + 3 NiBr₂ → 2 AlBr₃ + 3 Ni

a) No reaction occurs.

b) Fe(NO₃)_iii + Al → Al(NO₃)_three + Fe

a) two NaI + Cl₂ → 2 NaCl + I₂

b) No reaction occurs.

11.

a) Zn(NO₃)_ii + 2 NaOH → Zn(OH)₂ + two NaNO₃

b) 2 HCl + Na₂S → 2 NaCl + H₂S

13.

a) Pb(NO₃)_ii + 2 KBr → PbBr_two + ii KNO₃

b) Thou₂O + MgCO_three → K₂CO_iii + MgO

xv.

a) Pb(NO₃)₂ + two KBr → PbBr₂(s) + 2 KNO_iii

b) No reaction occurs.

17.

a) two Grand_threePO_iv + 3 SrCl₂ → Sr₃(PO₄)_two(s) + 6 KCl

b) ii NaOH + MgCl₂ → 2 NaCl + Mg(OH)₂(s)