LecturesTeachers Guide

What is Double Replacement Reaction? Example

Double Replacement Reaction

What is Double Replacement Reaction? Example

Double Replacement Reaction: Let’s imagine ourselves going to a dance and having a dance partner. Once we arrive, we interact with other people, and we end up switching dance partners with another person. Now you end up with a new dance partner. The same kind of thing can be compared to what occurs in a double displacement reaction in chemistry.

double displacement reaction, also known as a double replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.

Double Replacement Reaction
Double Replacement Reaction

Double Replacement Reaction Worksheet

Just like how dance partners can be switched, the products of a double displacement reaction are the result of the cations and anions of the reactants trading partners with each other. Now we’ll learn the steps to complete and predict the correct products for a double displacement reaction. Let’s start with a look at the chemical reaction between Na 2 S and HCl.

Double Replacement Reaction 1
Double Replacement Reaction 1

Step 1: Identify the Individual Ions from the Reactants and Their Charges

For the reactant Na 2 S , there is a cation (positive ion) and an anion (negative ion). Na is written first, so that means Na is the cation. S is written second, so S is the anion. Cations and anions have charges that are either positive or negative integers. A cation has a positive charge, and an anion has a negative charge.

S has no subscript, which is just the small numbers at the bottom right after each element. No subscripts mean that the subscripts are equal to one. This means that if we rewrite the compound Na 2, the subscript for S is 1. We can then reverse the subscripts and figure out the individual charges of Na and S. Na has a charge of +1, and S has a charge of -2, as shown here:

Double Replacement Reaction 2
Double Replacement Reaction 2

Now, let us take a look at the other reactant, HCl. The cation is H, and the anion is Cl. Like we did with Na 2 S , we reverse the subscripts to figure out the individual charges.

Double Replacement Reaction 3
Double Replacement Reaction 3

Step 2: Switch the Cations and Anions of the reactants

To predict the products, bring down the charges as shown in this illustration:

Double Replacement Reaction 4
Double Replacement Reaction 4

Originally, the pairs are Na-S and H-Cl. Now, the new partner of Na is Cl, and the new partner of H is S.

Step 3: Balance the Chemical Reaction

The reaction, in this case, is not balanced, because the number of Na and H atoms (in red) is not the same.

Double Replacement Reaction 5
Double Replacement Reaction 5

What we need to do next is to balance the reaction by adding coefficients, which are the numbers before each compound. In this case, we will put a 2 in front of HCl to balance the H atoms and a 2 in front of NaCl to balance the Cl atoms.

double replacement reaction 6
double replacement reaction 6

Now, we have successfully balanced the reaction.

Double Replacement Reaction Examples

For our first example, we’ll look at the reaction between Li 2 SO 4 and BaCl2 . SO4 is a polyatomic ion, so we will treat this as one anion. The ion SO4 does not have a subscript (4 is not the subscript because this is included in the ion). The subscript of SO4 is 1. Let’s first determine the ions and their charges.

Double Replacement Reaction Example 1
Double Replacement Reaction Example 1

Now, we can switch the ions and come up with the double displacement reaction.

Double Replacement Reaction Example 2
Double Replacement Reaction Example 2

For our next example, let’s look at the reaction between NaOH and CaBr2 . For this reaction, OH is a polyatomic ion and is treated as one whole anion. The individual ions and the charges for these two reactants are demonstrated in this image:

Double Replacement Reaction Example 3
Double Replacement Reaction Example 3

Now, we can switch the ions, as you can see here:

Double Replacement Reaction Example 4
Double Replacement Reaction Example 4

Double Replacement Reaction Definition

double displacement reaction, also known as a double replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.

Double Replacement Reaction Calculator

A double replacement reaction will occur if a formation of a precipitate, gas or water takes place. Select two compounds above and this calculator will predict whether or not the reaction will occur in water. This is simply based on the solubility chart of inorganic compounds. It must be noted that the results are not 100% physically correct although they agree to a considerable extent.

Double Replacement Reaction Examples In Real Life

A double displacement reaction is a type of reaction where two reactants exchange ions to form two new compounds. Double displacement reactions typically result in the formation of a product that is a precipitate.

Double displacement reactions take the form:
AB + CD → AD + CB

The reaction occurs most often between ionic compounds, although technically the bonds formed between the chemical species may be either ionic or covalent in nature. Acids or bases also participate in double displacement reactions. The bonds formed in the product compounds are the same type of bonds as seen in the reactant molecules. Usually, the solvent for this type of reaction is water.

Alternative Terms

A double displacement reaction is also known as salt metathesis reaction, double replacement reaction, exchange, or sometimes a double decomposition reaction, although that term is used when one or more of the reactants does not dissolve in the solvent.

Double Displacement Reaction Examples

The reaction between silver nitrate and sodium chloride is a double displacement reaction. The silver trades its nitrite ion for the sodium chloride ion, causing the sodium to pick up the nitrate anion.
AgNO3 + NaCl → AgCl + NaNO3

Here’s another example:

BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaCl(aq)

How To Recognize a Double Displacement Reaction

The easiest way to identify a double displacement reaction is to check to see whether or not the cations exchanged anions with each other. Another clue, if the states of matter are cited, is to look for aqueous reactants and the formation of one solid product (since the reaction typically generates a precipitate).

Types of Double Displacement Reactions

Double displacement reactions may be classified into several categories, including counter-ion exchange, alkylation, neutralization, acid-carbonate reactions, aqueous metathesis with precipitation (precipitation reactions), and aqueous metathesis with double decomposition (double decomposition reactions). The two types most commonly encountered in chemistry classes are precipitation reactions and neutralization reactions.

A precipitation reaction occurs between two aqueous ionic compounds to form a new insoluble ionic compound. Here’s an example reaction, between lead(II) nitrate and potassium iodide to form (soluble) potassium nitrate and (insoluble) lead iodide.

Pb(NO3)2(aq) + 2 KI(aq) → 2 KNO3(aq) + PbI2(s)

The lead iodide forms what is called the precipitate, while the solvent (water) and soluble reactants and products are termed the supernate or supernatant. The formation of a precipitate drives the reaction in a forward direction, as the product leaves the solution.

Neutralization reactions are double displacement reactions between acids and bases. When the solvent is water, a neutralization reaction typically produces an ionic compound–a salt. This type of reaction proceeds in the forward direction if at least one of the reactants is a strong acid or a strong base. The reaction between vinegar and baking soda in the classic baking soda volcano is an example of a neutralization reaction. This particular reaction then proceeds to release a gas (carbon dioxide), which is responsible for the fizz of the reaction. The initial neutralization reaction is:

NaHCO3 + CH3COOH(aq) → H2CO3 + NaCH3COO

You’ll notice the cations exchanged anions, but the way the compounds are written, it’s a bit trickier to notice the anion swap. The key to identifying the reaction as double displacement is to look at the atoms of the anions and compare them on both sides of the reaction.

 

Comment here