What is Double Displacement Reaction?

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Grade Level:

Class 12

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Definition

What is it?

A double displacement reaction is a type of chemical reaction where two compounds react, and the positive and negative ions of the reacting compounds switch places. It's like two pairs of dance partners swapping partners to form two new pairs.

Simple Example

Quick Example

Imagine two groups of friends, Group A (Rohan and Priya) and Group B (Amit and Seema). In a double displacement reaction, Rohan might swap with Amit, so now you have Rohan with Seema, and Amit with Priya. The original pairs (Rohan-Priya and Amit-Seema) are gone, and new pairs (Rohan-Seema and Amit-Priya) are formed.

Worked Example

Step-by-Step

Let's look at the reaction between Silver Nitrate (AgNO3) and Sodium Chloride (NaCl).

Step 1: Identify the reactants: Silver Nitrate (AgNO3) and Sodium Chloride (NaCl).
---Step 2: Break down each reactant into its ions. AgNO3 has Ag+ (silver ion) and NO3- (nitrate ion). NaCl has Na+ (sodium ion) and Cl- (chloride ion).
---Step 3: The positive ion from the first compound (Ag+) swaps with the positive ion from the second compound (Na+).
---Step 4: The new pairs form. Ag+ combines with Cl- to form AgCl (Silver Chloride). Na+ combines with NO3- to form NaNO3 (Sodium Nitrate).
---Step 5: Write the balanced chemical equation: AgNO3 (aq) + NaCl (aq) --> AgCl (s) + NaNO3 (aq).

Answer: Silver Nitrate reacts with Sodium Chloride to produce Silver Chloride and Sodium Nitrate.

Why It Matters

Understanding double displacement reactions helps engineers design new materials and medicines, for example, in creating specific pigments for paints or developing water purification systems. Chemists use this knowledge in quality control for food and drug safety, ensuring the right compounds are present. It's also crucial in environmental science to remove pollutants from water.

Common Mistakes

MISTAKE: Students often think only one ion pair swaps. | CORRECTION: Remember, it's a 'double' displacement, meaning both positive ions (or negative ions) swap partners completely, leading to two new compounds.

MISTAKE: Forgetting to check if a precipitate, gas, or water is formed. | CORRECTION: Double displacement reactions usually result in the formation of a precipitate (an insoluble solid), a gas, or water. Always look for these indicators.

MISTAKE: Not balancing the chemical equation after writing the products. | CORRECTION: After identifying the products, always ensure the number of atoms of each element is the same on both sides of the reaction arrow to follow the law of conservation of mass.

Practice Questions

Try It Yourself

QUESTION: When Barium Chloride (BaCl2) reacts with Sodium Sulfate (Na2SO4), what are the products? | ANSWER: Barium Sulfate (BaSO4) and Sodium Chloride (NaCl)

QUESTION: Identify the type of reaction and complete the following: FeS (s) + 2HCl (aq) --> ? + ? | ANSWER: This is a double displacement reaction. Products are FeCl2 (aq) and H2S (g).

QUESTION: A student mixes a solution of Potassium Iodide (KI) with a solution of Lead Nitrate (Pb(NO3)2). What type of reaction occurs, and what is the insoluble product formed? Write the balanced equation. | ANSWER: Double displacement reaction. Insoluble product is Lead Iodide (PbI2). Balanced equation: 2KI (aq) + Pb(NO3)2 (aq) --> PbI2 (s) + 2KNO3 (aq).

MCQ

Quick Quiz

Which of the following is an example of a double displacement reaction?

C + O2 --> CO2

2Na + Cl2 --> 2NaCl

AgNO3 + NaCl --> AgCl + NaNO3

Zn + H2SO4 --> ZnSO4 + H2

The Correct Answer Is:

Option C shows the silver ion (Ag+) and sodium ion (Na+) swapping partners, forming two new compounds. Options A and B are combination reactions, and Option D is a single displacement reaction.

Real World Connection

In the Real World

In water treatment plants across India, double displacement reactions are used to remove harmful ions from drinking water. For instance, calcium and magnesium ions that cause 'hard water' can be removed by adding chemicals like sodium carbonate, which react to form insoluble precipitates that can then be filtered out, making the water safe and soft for daily use.

Key Vocabulary

Key Terms

ION: An atom or molecule with an electrical charge | PRECIPITATE: An insoluble solid formed during a chemical reaction in a liquid solution | REACTANT: A substance that takes part in and undergoes change during a reaction | PRODUCT: A substance formed as a result of a chemical reaction | AQUEOUS SOLUTION: A solution in which the solvent is water

What's Next

What to Learn Next

Next, you should explore 'Single Displacement Reactions' to understand how they differ from double displacement reactions. Then, learn about 'Redox Reactions' which are crucial for many energy-related processes, building on your understanding of how elements change partners.