Why is Specific Rotation Not a Colligative Property? Answers Here

[pseudogirl]

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?

 

[Borek]

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

 

[pseudogirl]

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*cl=length of polarimeter tube
c=concentration of optically active solution in (gm/l)why is molarity not there in the formula?

 

[Borek]

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.

 

[DeeNos]

You have a valid point. Specific rotation is not a colligative property because it is dependent on the molecular structure of the substance, rather than just its concentration. Colligative properties, such as boiling point elevation and freezing point depression, are only affected by the number of particles present in a solution, not the type or structure of the particles. Therefore, specific rotation is not considered a colligative property.