Refractrometry for 1st sem By Vinod kumar mulge Department of chemistry

PERCANTAGE COMPOSITION OF UNKNOWN MIXTURE ‘C’ BY FORMULA METHOD AIM :To determine the refractive indices and specific refractivities of liquids A and B to determine the percentage of unknown mixture of ‘C’ . Apparatus : Abbe’s refractometer, Dropper, Cotton ,Specific gravity bottle Chemicals : Benzene ,Carbon tetrachloride ,mixtures Theory :When a beam of light passed from one medium to another , it suffers refraction i.e change of direction .If it passes from less dense (Air) to a more dense medium (Liquid) it refracts towards the normal .The refractive index of the medium with respect to first is given by Sin ‘I’=n –refractive index   Specific refractivity is determined by R=n2- 1 r=Specific refractivity d=density of liquid Molecular refractivity RM = R M = Molecular weight of medium

Procedure: 1)Place the Refractometer on the table near a window so that sufficient light reaches to the prism 2)Open the prism box by turning the lock nut . Clean the faces of both prisms with the help of cotton dipped in acetone or alcohol . Allow the surface to dry up . 3) Place few drops of liquid under examination carefully and close than prism . 4)Focus the cross wire of telescope by rotating the eye piece and adjust the mirror to reflect maximum light into the prism box. 5)Move the prism box backward and forward until clear boundary between light and dark region appear. 6)Now rotate the prism box until the sharp boundary line coincide with the intersection of the cross wire in the telescope. 7)Read the refractive index directly on the scale Repeat the readings at least 3 time and take the mean . 8)Determine the density of liquid by using density bottle and record the observations in the tabular column. Observation:

Observation Liquids Percentage Composition of ‘A’ Density Refractive Index R= A B M1 M2 M3 C

Calculation- (a)Determination of density of ‘C’ mixture 1)Weight of the empty specific gravity bottle W1=……………… 2)Weight of the empty specific gravity bottle + mixture W2=……………. 3)Weight of the empty specific gravity bottle + distilled water W3 =…………. Density of mixture ‘C’ =Weight of liquid/Weight of the water=W2-W1/W3-W1 (b) Calculation of Percentage of Composition of the Mixture (1)Percentage of composition by formula method: Calculate percentage composition ‘C’ by using formula 100RC=PRA + (100-P) RB PA=(RC-RB) X 100 (RA-RB) Where RA, RB &RC are specific refractivity of A, B & C respectively P=percentage of ‘A’ in the mixture ‘C’ .