Biomolecules and Chemistry in Everyday Life 1 Question 25
27. For ‘invert sugar’, the correct statement(s) is (are) (Given: specific rotations of $(+)$ - sucrose, $(+)$ - maltose, $\mathrm{L}-(-)$-glucose and $\mathrm{L}-(+)$-fructose in aqueous solution are $+66^{\circ},+140^{\circ},-52^{\circ}$ and $92^{\circ}$, respectively)
(2016 Adv.)
(a) Invert sugar is prepared by acid catalysed hydrolysis of maltose
(b) Invert sugar is an equimolar mixture of D-(+) -glucose and $\mathrm{D}$-(-)- fructose
(c) Specific rotation of invert sugar is $-20^{\circ}$
(d) On reaction with $\mathrm{Br}_{2}$ water, invert sugar forms saccharic acid as one of the products
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Solution:
- If there is inversion of specific rotation from (+) to (-), then invert sugar is formed.
(a) $\mathrm{C}{12} \mathrm{H}{22} \mathrm{O}{11}+\mathrm{H}{2} \mathrm{O} \longrightarrow$ Glucose
(b) $\mathrm{C}{12} \mathrm{H}{22} \mathrm{O}{11}+\mathrm{H}{2} \mathrm{O} \longrightarrow$ Glucose + Fructose
There is formation of invert sugar. Thus, correct.
(c) Specific rotation of invert sugar is $-20^{\circ}$ per mole. Thus, correct.
(d) $\mathrm{Br}{2}$ water is a weak oxidising agent. It oxidises $-\mathrm{CHO}$ to $-\mathrm{COOH}$ - $\mathrm{CH}{2} \mathrm{OH}$ group is not affected.
Saccharic acid
Gluconic acid (one of the products)
$\mathrm{HNO}_{3}$ (a strong oxidising agent) oxidises invert sugar to saccharic acid. Thus, incorrect.
