(a) Define a double displacement reaction. (b) Write the chemical equation of a double displacement reaction which is also a (i) Neutralization reaction and (ii) Precipitation reaction. Give justification for your answer.

Q: (a) Define a double displacement reaction. (b) Write the chemical equation of a double displacement reaction which is also a (i) Neutralization reaction and (ii) Precipitation reaction. Give justification for your answer.

(a) **Double Displacement Reaction:** A chemical reaction in which there is an exchange of ions between the reactants to form new compounds is called a double displacement reaction. (b) (i) **Neutralization Reaction:** * **Chemical Equation:** $$NaOH(aq) + HCl(aq) ightarrow NaCl(aq) + H_2O(l)$$ * **Justification:** In this reaction, sodium hydroxide (a base) reacts with hydrochloric acid (an acid) to form sodium chloride (salt) and water. There is an exchange of ions between the reactants: the sodium ion ($Na^+$) combines with the chloride ion ($Cl^-$), and the hydrogen ion ($H^+$) combines with the hydroxide ion ($OH^-$). Since it involves an exchange of ions, it is a double displacement reaction. Because an acid and a base react to neutralize each other and form salt and water, it is also a neutralization reaction. (ii) **Precipitation Reaction:** * **Chemical Equation:** $$BaCl_2(aq) + Na_2SO_4(aq) ightarrow BaSO_4(s) + 2NaCl(aq)$$ * **Justification:** In this reaction, aqueous solutions of barium chloride and sodium sulphate react to form a white insoluble solid, barium sulphate ($BaSO_4$), which precipitates out of the solution, along with soluble sodium chloride. There is an exchange of ions: barium ions ($Ba^{2+}$) combine with sulphate ions ($SO_4^{2-}$), and sodium ions ($Na^+$) combine with chloride ions ($Cl^-$). Since there is an exchange of ions, it is a double displacement reaction. Because an insoluble precipitate is formed, it is also a precipitation reaction.

Chemical Reactions and Equations

Types of Chemical Reactions

Official Answer

(a) Double Displacement Reaction: A chemical reaction in which there is an exchange of ions between the reactants to form new compounds is called a double displacement reaction.

(b) (i) Neutralization Reaction:

Chemical Equation:

$NaOH(aq) + HCl(aq) ightarrow NaCl(aq) + H_2O(l)$

Justification: In this reaction, sodium hydroxide (a base) reacts with hydrochloric acid (an acid) to form sodium chloride (salt) and water. There is an exchange of ions between the reactants: the sodium ion ( $Na^+$ ) combines with the chloride ion ( $Cl^-$ ), and the hydrogen ion ( $H^+$ ) combines with the hydroxide ion ( $OH^-$ ). Since it involves an exchange of ions, it is a double displacement reaction. Because an acid and a base react to neutralize each other and form salt and water, it is also a neutralization reaction.

(ii) Precipitation Reaction:

Chemical Equation:

$BaCl_2(aq) + Na_2SO_4(aq) ightarrow BaSO_4(s) + 2NaCl(aq)$

Justification: In this reaction, aqueous solutions of barium chloride and sodium sulphate react to form a white insoluble solid, barium sulphate ( $BaSO_4$ ), which precipitates out of the solution, along with soluble sodium chloride. There is an exchange of ions: barium ions ( $Ba^{2+}$ ) combine with sulphate ions ( $SO_4^{2-}$ ), and sodium ions ( $Na^+$ ) combine with chloride ions ( $Cl^-$ ). Since there is an exchange of ions, it is a double displacement reaction. Because an insoluble precipitate is formed, it is also a precipitation reaction.

exchange of ionsneutralizationprecipitationinsolublesalt and waterprecipitate

Marking Scheme

11 mark: Correct definition of double displacement reaction.
21 mark: Correct balanced chemical equation with state symbols and justification for the neutralization reaction.
31 mark: Correct balanced chemical equation with state symbols and justification for the precipitation reaction.

Hint

Recall that double displacement reactions involve the exchange of ions. For neutralization, think of an acid reacting with a base. For precipitation, think of a reaction that forms an insoluble solid.

Quick Oral Answer

A double displacement reaction is a reaction in which two compounds exchange their ions to form two new compounds. An example of a neutralization double displacement is the reaction between sodium hydroxide and hydrochloric acid to form sodium chloride and water.

Analysis & Explanation

A double displacement reaction is characterized by the mutual exchange of ions between two reacting ionic compounds.

In the neutralization reaction between $NaOH$ and $HCl$ , the reactants exchange their respective cations and anions ( $Na^+$ with $Cl^-$ and $H^+$ with $OH^-$ ) to produce a salt ( $NaCl$ ) and water ( $H_2O$ ). Since the acidic and basic properties are neutralized, it is classified as a neutralization reaction.
In the precipitation reaction between $BaCl_2$ and $Na_2SO_4$ , the exchange of ions ( $Ba^{2+}$ with $SO_4^{2-}$ and $Na^+$ with $Cl^-$ ) results in the formation of barium sulphate ( $BaSO_4$ ), which is insoluble in water and separates out as a white precipitate. Hence, it is classified as a precipitation reaction.

Common Mistakes

1Forgetting to write the physical states of the reactants and products (e.g., (aq), (s), (l)).
2Writing unbalanced chemical equations.
3Confusing single displacement (where a more reactive element displaces a less reactive one) with double displacement (where ions are mutually exchanged).

Interesting Facts

The chemical formula of marble is $CaCO_3$ , which is also formed when slaked lime reacts with carbon dioxide on walls.

Precipitation reactions are widely used in industries to precipitate out specific ions from wastewater to purify it.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 3 marks in the CBSE Class 10 Science 2023 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Types of Chemical Reactions" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This is a Short Answer question from Section C in the CBSE Class 10 Science 2023 paper.