Question

a. In this equation for specific rotation of a solution: a is the observed rotation in degrees, is the path length in decimetres, c is the concentration in g mL-1, Tis the temperature at which the measurement was taken in °C, and A is the wavelength in nanometres. You used variable path lengths for the polarised light (589 nm) to pass through, and you obtained the fol solutions (A, B, C, D and E) at variable concentrations. observed rotation data at 22°C for five unknown sugar Sugar Path length Sugar concn. Observed rotation 100 50 50 100 50 +0.70 -2.14 -9.20 +2.58 -0.90 10 20 From the table below, what are the most likely identities of the sugars? (For example, A Your sugar choice.) Specific rotation of some sugars at 20 C with the D line of sodium light Specific rotation Fructose Galactose Glucose Lactose Maltose -92.4 +80.2 +52.7 +55.4 +130.5 +14.2 -42.9 +66.5 +18.8 Xylose b. When glucose is dissolved in water, what happens within several hours to the observed rotation of polarised light at 589 nm? And why does this occur? A vineyard worker used a refractometer to measure the sugar concentration in grapes ready for harvest. She got an average refractive index of 1.3740 which means 26% (w/v) sucrose c.

Answer 1

Hey

Answer to question a)

identities of sugar-
The data in table represents that they have a positive specific rotation

this means they (most of sugar)are dextrorotatory.This means when a plane polarised light(which has vibration only in one plane like only in x or y or z direction) is passed through a sugar solution then

the light is rotated in clockwise direction.

b)glucose can exist in chain structure as well as in cyclic structure called(glucopyranose or haworth structure).there are 2 types of cyclic structure of glucose alpha and beta

when the OH attached to first carbon is below the plane of the ring, it is called an alpha structure

when it is below the plane of the ring it is called a beta structure.

The cyclic structure of glucose in water opens up into linear one and again closes(now when it closes it has 2 options either to go in alpha state or in beta)

beta cyclic structure is more stable because all OH groups are equatorial.while in alpha the first OH is axial and all other are equatorial so, there occurs an equilibrium between alpha, beta and linear structure, After some time we obtain, 63% beta cyclic structure and 36% alpha structure.

The rotation of alpha glucopyranose is +112degree and that of beta is +19

so, after long time the rotation of the mixture is found to be +52.7 degree(since alpha and beta are in equilibrium the totation oof alpha decreases and beta increases to 52.7)

This phenomenon is called mutarotation.

C)not a question

Hope it helped

Thanks!!!