SCIENCE-10TH CBSE ANSWER KEY

         CARBON AND ITS COMPOUND(1-5) 
Question-1 Why does graphite conducts electricity, but not diamond?
Solution: In case of diamond, each carbon atom of a single crystal is surrounded by four other carbon atoms by covalent bonds such that they form four corners of a regular tetrahedron. Because of four covalent bonds with each carbon atoms there are no free electrons available. Due to the non-availability of free electrons within crystalline structure, diamond acts as a bad conductor of electricity.
 In case of graphite, every carbon atom in a single crystal is covalently bonded to three carbon atoms. As each carbon atoms has four valence electrons one valence electron is left free for each carbon atom. These free electrons can be easily made to flow within the crystalline structure of graphite by applying electric potential. Thus, graphite is a good conductor of electricity.
Question-2 Write three important uses of ethanol.
Solution: Ethanol is used as a solvent to dissolve varnishes, medicines and other organic compounds
It is used as beverage (for drinking as an intoxicant) in different forms, viz; Brandy, Whisky etc.,
It is used for industrial uses in the name of denatured spirit.
Question-3State what you will observe when sugar crystals is heated strongly.State what you will observe when sugar crystals is treated with conc. Sulphuric acid.
Solution: The sugar crystal will initially melt. Gradually, they turn brown and start swelling up. They give off large amount of steam. Finally black porous residue of carbon is left behind.
The sugar crystals will initially turn brown. Lot of frothing takes place with the evolution of large amount of heat and steam is given off. Finally a black porous residue of carbon is left behind.
Question-4 How are the molecules of aldehyde and Ketone structurally different?
Solution: In aldehyde, the carbon atom of the carbonyl group is attached to one alkyl group (R) and one hydrogen atom but in ketone, the carbonyl group is attached to two alkyl groups.
Question-5 What change has been made in the composition of detergents to make them biodegradable?

Solution: Detergents made from long chain hydrocarbons having the minimum branching in their molecules are degraded more easily.
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