Question

Enter your answer in the provided box. an aqueous solution containing 10 g of an optically pure substance was diluted to 500 ml with water and placed in a polarimeter tube 20 cm long. the measured rotation was −3.10°. calculate the specific rotation of this compound. [α] = °

Answer 1

Answer:

[α] = -77.5° / $\frac{\textup{dm-g}}{\textup{mL}}$

Explanation:

Given;

Mass of optically pure substance in the solution = 10 g

Volume of water = 500 mL

Length of the polarimeter, l = 20 cm = 20 × 0.1 dm = 2 dm

measured rotation = - 3.10°

Now,

The specific rotation ( [α] ) is given as:

[α] = $\frac{\alpha}{c\times l}$

here,

α is the measured rotation = -3.10°

c is the concentration

or

c = $\frac{\textup{Mass of optically pure substance in the solution}}{\textup{Volume of water}}$

or

c =  $\frac{10}{500}$

or

c = 0.02 g/mL

on substituting the values, we get

[α] = $\frac{-3.10^o}{0.02\times2}$

or

[α] = -77.5° / $\frac{\textup{dm-g}}{\textup{mL}}$