Question

The observed rotation of 2.0 gm of a compound in 10 ml of
solution in polarimeter tube of 25 cm long is +13.4º. What is
specific rotation of a compound?
(A) 67°
(B) 769
(C) 26.80
(D) 62.8°​

Answer 1

conc^n = wt/volume

= 2/10

= 0.2

specific rot. = observed rot. / ( length x conc)

specific rot. = 13.4 / (2.5 × 0.2)

( changed length form cm to dm)

specific rot. = 26.8°

hope it may help you :)

Answer 2

Given:

Weight = 2.0 g

Volume = 10 ml

Length = 25 cm = 2.5 dm

Observed rotation = +13.4°

To find:

Specific rotation

Solution:

• Concentration = $\frac{weight}{volume}$ = $\frac{2}{10}$ = 0.2M

• Specific rotation = $\frac{observedrotation}{length*concentration}$ = $\frac{+13.4}{2.5*0.2}$

• Specific rotation = +26.80°