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Science · 2024 · 5 marks
CBSE 2024 · Region 1 · Set 2 · Q34
(i)Define the term functional group. Identify the functional groups present in the following carbon compounds :
(I)(II)(ii)What happens when ethanol reacts with acidified potassium dichromate solution ? Write chemical equation for the reaction. Why is this reaction considered an oxidation reaction ?(iii)Write chemical equation for the reaction of ethanoic acid with sodium hydroxide.(i)Describe method of preparation of soap giving chemical equation for the reaction involved.(ii)Explain with diagram the mechanism of the cleansing action of soaps.
(i)
Define the term functional group. Identify the functional groups present in the following carbon compounds :
(I)
(II)
(ii)
What happens when ethanol reacts with acidified potassium dichromate solution ? Write chemical equation for the reaction. Why is this reaction considered an oxidation reaction ?
(iii)
Write chemical equation for the reaction of ethanoic acid with sodium hydroxide.
(i)
Describe method of preparation of soap giving chemical equation for the reaction involved.
(ii)
Explain with diagram the mechanism of the cleansing action of soaps.
Marking-scheme solution
(i) Functional Group: A hetero atom or group of atoms attached to the carbon chain, which gives specific properties to the carbon compounds.
(I) Ketone
(II) Carboxylic acid
(ii) Ethanoic acid is formed
\[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \xrightarrow[\text { Acidified } \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\text { Heat }]{ } \mathrm{CH}_{3} \mathrm{COOH}
\]
oxygen is added to ethanol and converts /oxidises ethanol to ethanoic acid.
(iii) \(\displaystyle \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{NaOH} \longrightarrow \mathrm{CH}_{3} \mathrm{COONa}+\mathrm{H}_{2} \mathrm{O}\)
OR
(B) (i) Soaps are prepared by heating an ester (animal fat / vegetable oil) with a base such as sodium hydroxide.
\[\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5} \xrightarrow[\text { Sodium ethanoate }]{\mathrm{NaOH}} \underset{\text { Sol }}{\mathrm{CH}} \mathrm{COONa}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}
\]
(ii) Ionic (hydrophilic) end of the soap interacts with water while the carbon chain(hydrophobic) interacts with oil. Thus micelles are formed. Emulsion is formed in the water. Soap micelles pull out the dirt and oil in water.
(i)
\(\displaystyle R=\rho \frac{l}{A}\)
\[\begin{aligned}
\rho & =\frac{\mathrm{R} \times \mathrm{A}}{\mathrm{l}} \\
& =\mathrm{Ohm} \times \frac{(\text { metre })^{2}}{\text { metre }}
\end{aligned}
\]
\[=\text { ohm meter } / \Omega \mathrm{m}
\]
(ii)
Here \(\displaystyle l=3 \mathrm{~m}, \mathrm{~A}=4 \times 10^{-7} \mathrm{~m}^{2}, \mathrm{R}=60 \Omega\)
\[\begin{aligned}
\rho & =\frac{R \times A}{l} \\
= & \frac{60 \times 4 \times 10^{-7}}{3} \\
& =80 \times 10^{-7} \Omega \mathrm{~m}
\end{aligned}
\]
Resistivity will not change.
because Resistivity does not depend on the dimension of the conductor / It only depends on the nature of the material.
(B)
(iii)
Here \(\displaystyle f=-12 \mathrm{~cm}, u=-18 \mathrm{~cm}, v=\) ?
Mirror formula \(\displaystyle \frac{1}{f}=\frac{1}{v}+\frac{1}{u} \quad\) or \(\displaystyle \frac{1}{v}=\frac{1}{f}-\frac{1}{u}\)
\[\frac{1}{v}=\frac{1}{-12}-\frac{1}{-18}
\]
\(\displaystyle \mathrm{v}=-36 \mathrm{~cm}\)
In front of the mirror at a distance of $\displaystyle 36$ cm from the pole of the mirror.
(iii)(B)
If pea plants with yellow seeds are crossed with plants of green seeds, it is found that in \(\displaystyle \mathrm{F}_{1}\) generation all the plants have yellow seeds. When \(\displaystyle \mathrm{F}_{1}\) plants are self-pollinated, it is found that in \(\displaystyle \mathrm{F}_{2}\) generation, plants with yellow seeds and plants with green seeds are obtained. This shows that both the traits are inherited but only one trait is visible in \(\displaystyle \mathrm{F}_{1}\) progeny while the other remains unexpressed.
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.