Specific rotation

Why is specific rotation not a colligative property?
i just read that it depends on concentration(gm/litre)
but i feel that it should depend on molarity considering the fact that rotation is due to changes in molecular structure....do i have a point or am i just being silly ...can someone help me?

Last edited:

Borek
Mentor
Looks to me like you are confusing rotation with specific rotation.

i am sorry .i did confuse them both
so does rotation depend on number of moles per liter?

this is the formula in the book

specific rotation=rotation/l*c

l=length of polarimeter tube
c=concentration of optically active solution in (gm/l)

why is molarity not there in the formula?

Borek
Mentor
so does rotation depend on number of moles per liter?

Yes.

c=concentration of optically active solution in (gm/l)

why is molarity not there in the formula?

Does it have to be there? Concentration in the definition is expressed in g/L, g/L and molarity are easily interconvertible.