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Science · 2023 · 5 marks
CBSE 2023 · Region 6 · Set 2 · Q34
(i)What are isomers ? Write the structures of two compounds having molecular formula $\displaystyle \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}$ and give their names.(ii)What are soaps ? How are they chemically different from detergents ? Why do soaps not work effectively in hard water ?(i)What is a homologous series of carbon compounds ? Write general formula for alkynes. Name and draw the electron dot structure of first homologue of this series.(ii)State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols and carboxylic acids.
(i)
What are isomers ? Write the structures of two compounds having molecular formula $\displaystyle \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}$ and give their names.
(ii)
What are soaps ? How are they chemically different from detergents ? Why do soaps not work effectively in hard water ?
(i)
What is a homologous series of carbon compounds ? Write general formula for alkynes. Name and draw the electron dot structure of first homologue of this series.
(ii)
State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols and carboxylic acids.
Marking-scheme solution
(i)
Compounds having same molecular formula but different structural
formula
Structures are :
Propanal
Propanone
(ii)
-Soaps are sodium or potassium salts of long-chain carboxylic acids /
$\displaystyle \mathrm{R}-\mathrm{COO}^{-} \mathrm{Na}^{+}$
detergents are ammonium salts with chlorides or bromides ions or
Sodium salts of sulphonic acids/ $\displaystyle \mathrm{R}-\mathrm{OSO}_{3}{ }^{-} \mathrm{Na}^{+}$
Soaps react with calcium or magnesium ions present in hard water to
form an insoluble substance / soaps react with hard water forming scum.
(i)
A series of compounds in which the same functional group substitutes
for hydrogen in a carbon chain / having similar chemical. properties and
differ by $\displaystyle -\mathrm{CH}_{2}$.
General formula $\displaystyle \mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}-2}$
Ethyne
Electronic dot structure
(ii)
Functional group is an atom or a group of atoms (hetero atom) bonded
to a carbon chain. It defines the chemical property of the organic
compound.
Alcohol - OH
Carboxylic Acid
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CBSE Class 10 Science past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.