Question

20 gm of cane sugar is dissolved in water to make 50 c.c. of solution. A 20cm. length of the solution causes +53° optical rotations. Calculate the specific rotation? 
1. 93.78° 
2. 51.42° 
3. 65.25° 
4. 40.56° 

Answer 1

Correct Answer - Option 3 : 65.25° 

Concept:

The specific rotation of a solution is given as:

\({S } = \frac{{10θ }}{{lc}}\)        ----(1)

Where,

l is the length of the tube in cm

θ is the rotation of the plane of polarization

c is the strength of the solution

S is the specific rotation of sugar

Calculation:

Given:

θ = +53°, l = 20 cm

\(c=\frac{20}{50}=0.40 \ gm/cc\)

From equation 1);

\({S } = \frac{{10\;\times\;53^0 }}{{20\;\times\; 0.40}}\)

S = 66.25⁰ cm³/g-dm