EXPERIMENT 23

OVERVIEW

GOAL

DETERMINE MOLAR MASS OF Sx

AND THE VALUE OF x

METHOD

FREEZING POINT DEPRESSION

Freezing point depression can be used to find molar mass of solute

∆Tf ― experiments

i ― electrolyte or nonelectrolyte

Kf ― table or reference book

f

f

KiΔT

solventofkilogramsoluteofmolesm

f

fff Ki

ΔTm m Ki ΔT

soluteofmolessolute of masssolute of massmolar

Solute: Sx Solvent: Naphthalene

i = 1 Kf: given

ΔTf = Tf,solvent − Tf,solution

Tf,solvent: Part A

Tf,solution: Part B

Kilogram of naphthalene: balance

Mass of Sx: balance

PROCEDURE AND SAFETY• FOLLOW PROCEDURES IN LAB MANUAL

EXCEPT: WORK AT BENCH

• USE THE SAME THERMOMETER

• PLACE TUBE ON BALANCE PROPERLY

• COVER LIDS AFTER WEIGHING

• DO NOT MIX SPETULAS

PROCEDURE AND SAFETY• ALL WASTE GOES IN BROWN WASTE

BOTTLE IN HOOD, NOT SINK! USE ACETONE TO RINSE RESIDUE INTO PLASTIC WASTE CONTAINER

• STAY AWAY FROM THE HOTPLATE WHILE COOLING

• RETURN ALL COMMON ITEMS

PROCEDURE AND SAFETY

•CLEAN YOUR AREA BEFORE LEAVING AND ASK FOR INSPECTION

DATA ANALYSIS

Tem

pera

ture

(°C

)

Time (min)

Tf

Cooling Curve

liquid

liquid + solidsolid

GRAPHING• USE SOFTWARE TO FIND Tf

• USE FULL PAGE: CHOOSE SCALE PROPERLY

• GIVE GRAPH A TITLE

• LABEL AXIS, ADD LEGEND

• EXAMPLE

Kaleidagraph

SigmaPlot

Origin

Graphing Software