JEE Main 2024 · Chemistry · Biomolecules and Polymers · medium

42 g of sucrose is completely hydrolysed and the solution is made up to 100 mL. Specific rotations: glucose +52.5^°, fructose -92.4^° (in deg mL g^-1…

Single correct option

3.42\ \mathrm{g}

of sucrose is completely hydrolysed and the solution is made up to

100\ \mathrm{mL}

. Specific rotations: glucose

+52.5^\circ

, fructose

-92.4^\circ

(in

\mathrm{deg\,mL\,g^{-1}\,dm^{-1}}

). The observed rotation in a

10\ \mathrm{cm}

tube is nearly (molar mass of sucrose

=342

)

Show answer and solution

Answer: (A) $-0.72^\circ$

3.42\ \mathrm{g}=0.0100

mol sucrose gives

0.0100

mol each of glucose and fructose (

180\ \mathrm{g\,mol^{-1}}

), i.e.

1.80\ \mathrm{g}

of each in

100\ \mathrm{mL}

c=0.018\ \mathrm{g\,mL^{-1}}

. Path length

l=1\ \mathrm{dm}

\alpha=\sum[\alpha]cl=(52.5-92.4)(0.018)(1)=-0.718^\circ

. The negative sign (inversion of sugar) is because fructose rotates more strongly than glucose.

Original question written in the JEE Main 2024 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake