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7.5 - Exercises

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Redox Reaction Fundamentals

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Teacher
Teacher

Let's discuss what a redox reaction is. Does anyone want to explain it?

Student 1
Student 1

Isn't redox a combination of reduction and oxidation?

Teacher
Teacher

Exactly! Redox reactions involve the transfer of electrons, where one species is oxidized and another is reduced. A mnemonic to remember is 'OIL RIG' — Oxidation Is Loss and Reduction Is Gain. Can anyone give an example of a redox reaction?

Student 2
Student 2

How about the reaction between hydrogen and oxygen to form water?

Teacher
Teacher

Great example! In that reaction, hydrogen is oxidized, and oxygen is reduced. Let's summarize that oxidation involves increasing oxidation states and reduction, a decrease.

Assigning Oxidation Numbers

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Teacher
Teacher

Now that we understand redox basics, who can tell me why oxidation numbers are important?

Student 3
Student 3

They help us identify the oxidation state of elements, right?

Teacher
Teacher

Absolutely! Understanding oxidation states helps us balance redox equations too. Let’s practice assigning oxidation numbers in a compound. What is the oxidation state of phosphorus in H2PO4?

Student 4
Student 4

I think it's +5, since the overall charge is neutral?

Teacher
Teacher

Correct! Remember, in compounds, the oxidation numbers must always sum to the charge of the compound.

Balancing Redox Equations

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Teacher
Teacher

Let’s dive deeper into balancing redox equations. Who can explain how the half-reaction method works?

Student 1
Student 1

Isn't it when you separate the oxidation and reduction reactions and balance them individually?

Teacher
Teacher

Exactly! After balancing, we then combine them to form the complete balanced equation. Can anyone balance the equation for the reduction of MnO4— to MnO2?

Student 2
Student 2

After balancing the Mn, we also have to balance the oxygen and hydrogen by adding water and protons!

Teacher
Teacher

Very good! Let's summarize: balancing involves identifying changes in oxidation states and ensuring both mass and charge balance.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section covers exercises pertinent to redox reactions, including balancing equations and identifying oxidation states.

Standard

In this section, various exercises help students apply their understanding of redox reactions, such as identifying oxidation states, justifying redox processes, and balancing equations. The exercises cater to different difficulty levels and reinforce key concepts in the topic.

Detailed

This section presents a variety of exercises designed to reinforce key concepts surrounding redox reactions. Students will find assignments that challenge them to assign oxidation numbers to particular elements, justify whether specific reactions are redox processes, and balance redox reactions using different methods. The exercises are categorized into easy, medium, and hard levels to provide a progressive learning experience. Additionally, the section includes reflection questions and case-based discussions to foster critical thinking and application of theoretical knowledge.

Youtube Videos

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Redox Reactions Class 11 Chemistry | Chapter 8 Ncert Solutions Questions 20-24
Redox Reactions Class 11 Chemistry | Chapter 8 Ncert Solutions Questions 20-24
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Redox Reactions Class 11 Chemistry | Chapter 8 Ncert Solutions Questions 1-8
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Redox Reactions - NCERT Intext Questions (Q. 1 to 10) | Class 11 Chemistry Chapter 7 | CBSE 2024-25
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Questions on Balancing Redox Reactions | Class 11 Chemistry Chapter 7 | CBSE 2024-25 #live

Audio Book

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Oxidation Numbers Assignment

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7.1 Assign oxidation number to the underlined elements in each of the following species:
(a) NaH2PO4
(b) NaHSO4
(c) H4P2O7
(d) K2MnO4
(e) CaO2
(f) NaBH4
(g) H2S2O7
(h) KAl(SO4)2.12 H2O

Detailed Explanation

In this exercise, you are tasked with determining the oxidation numbers of specified elements within various chemical compounds. Oxidation numbers indicate the degree of oxidation (loss of electrons) of an atom in a chemical compound. To do this, recall the rules set forth for assigning oxidation numbers, such as the oxidation number of free elements being zero, the oxidation number of monoatomic ions being equal to their charge, and certain common oxidation states for particular elements (e.g., oxygen usually as -2, hydrogen as +1).

Examples & Analogies

Think of oxidation numbers like measuring the charge of a battery. Just like a fully charged battery has a certain energy level, each element in a compound has a specific oxidation number that reflects its 'charge' relative to its neutral state. For example, in water (H2O), hydrogen has a +1 oxidation number, indicating it is more 'positive' than when it is in its elemental form.

Rationalization of Results

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7.2 What are the oxidation number of the underlined elements in each of the following and how do you rationalise your results?
(a) KI3
(b) H2S4O6
(c) Fe3O4
(d) CH3CH2OH
(e) CH3COOH

Detailed Explanation

This exercise focuses on not just assigning oxidation numbers but also explaining how you arrived at your answers. This logical reasoning is key in chemistry. For instance, in KI3, potassium (K), a Group 1 metal, has a +1 oxidation state, while Iodine typically varies between -1 and +5 depending on its chemical environment. Rationalizing results requires an understanding of how different atoms interact based on their electronegativities and common oxidation states.

Examples & Analogies

Imagine a game where each player (element) has a score (oxidation number) that changes depending on the team they are playing on (chemical environment). A player like potassium always maintains a high score regardless of who they are playing with, while iodine’s score can change drastically based on the rules of the game (the environment created by its surrounding atoms).

Identification of Redox Reactions

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7.3 Justify that the following reactions are redox reactions:
(a) CuO(s) + H2(g) → Cu(s) + H2O(g)
(b) Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)
(c) 4BCl3(g) + 3LiAlH4(s) → 2B2H6(g) + 3LiCl(s) + 3 AlCl3(s)
(d) 2K(s) + F2(g) → 2K+F–(s)
(e) 4 NH3(g) + 5 O2(g) → 4NO(g) + 6H2O(g)

Detailed Explanation

In this exercise, students need to recognize and justify that the provided reactions involve electron transfer, which is the hallmark of redox processes. For example, in reaction (a), CuO is reduced to Cu while H2 is oxidized to H2O, demonstrating the simultaneous occurrence of oxidation and reduction. This concept is central to understanding how energy changes in chemical reactions and the flow of electrons.

Examples & Analogies

Think of redox reactions like a relay race where electrons are passed between runners; as one runner (an atom) sprints ahead to donate their baton (electrons), another runner is waiting to receive it, thus keeping the flow going. Just as the race cannot continue without passing the baton, a redox reaction cannot occur without the exchange of electrons.

Justification of Redox Reactions

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7.4 Fluorine reacts with ice and results in the change:
H2O(s) + F2(g) → HF(g) + HOF(g)
Justify that this reaction is a redox reaction.

Detailed Explanation

In this exercise, students need to analyze how fluorine reacts with ice and determine the changes in oxidation states. In this case, fluorine is reduced as it gains electrons and achieves a more stable electronic configuration. The compound H2O loses some hydrogen atoms, demonstrating its role as a reducing agent. The recognition of this transfer is fundamental to classifying the reaction as redox.

Examples & Analogies

Consider this reaction as a dramatic transformation in a movie where the hero (fluorine) breaks into a scene (ice), changes the narrative (reaction), and while doing so, transforms some characters (hydrogens) into different versions of themselves (HF and HOF), illustrating the classic tale of oxidation and reduction.

Calculation of Oxidation Numbers

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7.5 Calculate the oxidation number of sulphur, chromium and nitrogen in H2SO5, Cr2O72– and NO3–. Suggest structure of these compounds. Count for the fallacy.

Detailed Explanation

In this exercise, students will calculate the oxidation states of sulphur, chromium, and nitrogen in specified compounds. It requires an application of the oxidation rules while also emphasizing the need to visualize their molecular structures. Additionally, students should reflect on any discrepancies or inconsistencies in their calculations – a practice that enhances critical thinking in chemistry.

Examples & Analogies

Imagine trying to figure out how many cookies each friend brought to a party while some of them may have estimated incorrectly. Similarly, while calculating oxidation numbers, we must keep track of all elements to ensure no one is overestimated or underestimated, leading to hidden complexities that may arise from incorrect assumptions.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Redox Reactions: Involve simultaneous oxidation and reduction processes.

  • Oxidation Numbers: Assigned to keep track of electron loss or gain.

  • Balancing Equations: Essential skill in understanding redox processes.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • The reaction 2Na + Cl2 → 2NaCl showcases oxidation of sodium and reduction of chlorine.

  • In the combustion of methane, CH4 + 2O2 → CO2 + 2H2O, carbon is oxidized and oxygen is reduced.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • OIL RIG, it's easy as pie, Oxidation loses, Reduction is why.

📖 Fascinating Stories

  • Imagine two friends playing tug of war where one pulls the rope away (oxidation) and one pulls it towards them (reduction).

🧠 Other Memory Gems

  • LEO says GER: Lose Electrons = Oxidation, Gain Electrons = Reduction.

🎯 Super Acronyms

REDOX

  • Reduction and Oxidation.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Redox Reaction

    Definition:

    A chemical reaction where the oxidation state of one or more components changes due to electron transfer.

  • Term: Oxidation

    Definition:

    The process of an atom losing electrons, resulting in an increase in oxidation state.

  • Term: Reduction

    Definition:

    The process of an atom gaining electrons, resulting in a decrease in oxidation state.