SCIENCE-10TH CBSE ANSWER KEY

         CARBON AND ITS COMPOUND(6-9)
Question-6A hydrocarbon molecule contains 4 hydrogen atoms. Give its molecular formula, if it is an: (i) alkane, (ii) alkene (iii) alkyne.
Solution:(i) An alkane containing 4 hydrogen atoms in its molecule is methane, CH4.
(ii) An alkene containing 4 hydrogen atoms in its molecule is ethane, C2H4
(iii) An alkyne containing 4 hydrogen atoms in its molecule is propyne, C3H4.
Question-7  Why common salt is added in soap making?
Solution: Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution. Actually, when we add common salt to the solution, then the solubility of soap present in it decreases, due to which all the soap separates out from the solution in the form of a solid.
Question-8 What is meant by denatured alcohol? What is the need to denature alcohol?
Solution: The alcohol which is rendered unfit by mixing it with some poisonous substances, such as methanol, pyridine, copper sulphate, etc is known as denatured alcohol. Ethanol is an important industrial chemical. Therefore, it subjected to very small excise duty. To prevent its misuse for drinking purpose, there is a need to denature alcohol.
Question- What is meant by the term "functional group"?
Solution:A functional group in an organic compound is an atom or a group of atoms binded together in a unique fashion, which is usually the site of chemical reactivity in an organic molecule. 
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