Q7
3 marksShort AnswerSection A

With the help of an example, explain the process of hydrogenation. Mention the essential conditions for the reaction and state the change in physical property with the formation of the product.

Carbon and its Compounds
Chemical Properties of Carbon Compounds
Official Answer

Hydrogenation is an addition reaction where unsaturated hydrocarbons (alkenes or alkynes) add hydrogen in the presence of catalysts to become saturated hydrocarbons.


Example: The addition of hydrogen to ethene to form ethane.

CH2=CH2+H2→Ni/PdCH3−CH3CH_2=CH_2 + H_2 \xrightarrow{Ni/Pd} CH_3-CH_3


Essential Conditions:

  1. Presence of a catalyst such as Nickel (NiNi), Palladium (PdPd), or Platinum (PtPt).
  2. Presence of unsaturated carbon-carbon bonds (double or triple bonds).

Change in Physical Property:

This process is used to convert liquid vegetable oils (which are unsaturated) into solid vegetable ghee (which is saturated). Thus, the physical state changes from liquid to solid/semi-solid.

Addition reactionCatalystNickelUnsaturatedSaturatedVegetable oilVegetable ghee

Marking Scheme

  • 1Definition of hydrogenation and example equation (1 mark)
  • 2Essential conditions (Catalyst: Ni/Pd) (1 mark)
  • 3Physical property change: Liquid oil to solid fat (1 mark)

Hint

Think about how vegetable oil is converted into vegetable ghee using a catalyst.

Quick Oral Answer

Hydrogenation is the addition of hydrogen to unsaturated compounds using a catalyst like Nickel. It turns liquid oils into solid fats.

Analysis & Explanation

Hydrogenation is a specific type of addition reaction. In the presence of catalysts like finely divided nickel, the double bonds in unsaturated fats/oils break, and hydrogen atoms occupy the vacant valencies, resulting in a saturated compound. This reaction is industrially significant in the food industry for making margarine or vanaspati ghee from vegetable oils.

Common Mistakes

  1. 1Forgetting to mention the catalyst (Ni/Pd).
  2. 2Confusing addition reactions with substitution reactions.

Interesting Facts

Vegetable oils containing long unsaturated carbon chains are generally considered healthy, while saturated fats (like those produced by hydrogenation) can be harmful if consumed in excess.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2015?

This question carries 3 marks in the CBSE Class 10 Science 2015 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chemical Properties of Carbon Compounds" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2015 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2015 paper.