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Model Paper 5 — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 55 Marks
Question
1. Suggest a method to purify
i. a liquid which decomposes at its boiling point.
ii. kerosene oil containing water.
iii. camphor containing traces of common salt.
2. Giving justification, categorise the following molecules/ions as nucleophile or electrophile:
$
\begin{aligned}
& HS^{-}, BF_3, C_2 H_5 O^{-},\left(CH_3\right)_3 N:, \\
& C \stackrel{+}{l}, C H_3-\stackrel{+}{C}=O, H_2 N \stackrel{+}{:}, \stackrel{+}{N} O_2
\end{aligned}
$
✓

Answer

1. i. Distillation under reduced pressure.
ii. Since the two liquids are immiscible, the technique of solvent extraction with a separating funnel is used. Kerosene being lighter than water forms the upper layer while water forms the lower layer.
The lower water layer is run off when kerosene oil is obtained. It is dried over anhydrous $CaCl _2$ or $M _{ g } SO _4$ and then distilled to give pure kerosene oil.
iii. Sublimation Camphor sublimes while common salt remains as residue in the China dish.
2. Nucleophiles(reagent that brings electron pair): $HS ^{-}, C _2 H _5 O ^{-},\left( CH _3\right)_3 N$ :, $H _2 N$ :-
These species have unshared pair of electrons, which can be donated and shared with an electrophile.
Electrophiles(reagent which takes away electron pair): $BF _3, C \stackrel{+}{l}, CH _3-\stackrel{+}{ C }= O , \stackrel{+}{ N } O _2$
Reactive sites have only six valence electrons; can accept electron pair from a nucleophile.

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