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

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

Step-by-step 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] =
`(\alpha)/(c* 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 =
`(10)/(500)`

or

c = 0.02 g/mL

on substituting the values, we get

[α] =
`(-3.10^o)/(0.02*2)`

or

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