Q14
3 marksShort AnswerSection A

No chemical reaction takes place when granules of a solid, A, are mixed with the powder of another solid, B. However when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in the molten state while the other product, D, floats over it. It was observed that the reaction is highly exothermic. (i) Based on the given information make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of reaction. (ii) Mention any two types of reactions under which above chemical reaction can be classified.

Chemical Reactions and Equations
Types of Chemical Reactions
Official Answer

(i) Assumption: Solid A is Aluminum powder (AlAl) and Solid B is Iron(III) oxide (Fe2O3Fe_2O_3).

Chemical Equation:

Fe2O3(s)+2Al(s)→Heat2Fe(l)+Al2O3(s)+HeatFe_2O_3(s) + 2Al(s) \xrightarrow{\text{Heat}} 2Fe(l) + Al_2O_3(s) + \text{Heat}

In this reaction, the iron produced is in a molten (liquid) state due to the high temperature, and Aluminum oxide (Al2O3Al_2O_3) floats over it as it is less dense.


(ii) Types of Reactions:

  1. Displacement Reaction: Aluminum, being more reactive, displaces iron from its oxide.
  2. Exothermic Reaction: A large amount of heat is evolved during the reaction.
  3. Redox Reaction: Iron oxide is reduced to iron, and aluminum is oxidized to aluminum oxide.
Thermite reactionExothermicDisplacementMolten ironAluminum oxideRedox

Marking Scheme

  • 1Identification of A and B (Aluminum and Iron oxide) (1 mark)
  • 2Balanced chemical equation with state symbols and heat (1 mark)
  • 3Mentioning two reaction types (Displacement/Exothermic/Redox) (1 mark)

Hint

Think of the 'Thermite reaction' used to join railway tracks, where aluminum reacts with iron oxide to produce molten iron.

Quick Oral Answer

The reaction is called the Thermite reaction. It is a displacement reaction because Aluminum is more reactive than Iron. It is exothermic because it releases a massive amount of heat energy.

Analysis & Explanation

The reaction described is the Thermite reaction. Grounded in the text, an exothermic reaction is defined as one where 'heat is released along with the formation of products' (Section 1.2.1). The text also mentions Fe2O3Fe_2O_3 as a solid product in other reactions (Eq 1.19). In this specific scenario, the heat generated is so intense that the metal (Iron) is produced in a liquid state. Aluminum oxide, being a ceramic/slag, floats on top of the denser molten iron. This is a classic example of a displacement reaction where a more reactive element (Al) displaces a less reactive one (Fe).

Common Mistakes

  1. 1Writing iron as a solid (s)(s) instead of liquid (l)(l).
  2. 2Forgetting to mention 'Heat' in the equation despite the prompt saying it is highly exothermic.
  3. 3Incorrectly identifying the floating product.

Interesting Facts

The Thermite reaction is so hot (reaching over 2500∘C2500^{\circ}C) that it is used for on-site welding of railway tracks.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2010?

This question carries 3 marks in the CBSE Class 10 Science 2010 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 2010 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2010 paper.