Triple Point of Water Experiment

Phase Diagram and Triple Point of tert-Butanol ExperimentBy Michael Heynen & Biruk Gote

Boiling PointThe boiling point is the temperature at which the vapor pressure of a liquid equals the pressure of the systemAs the pressure of the system is reduced, the boiling point of a liquid is loweredLiquid GasMelting PointGenerally depends only slightly on pressure, mostly on intermolecular forcesIf the pressure of a system is varied, little change is observed

Solid LiquidTriple PointThe pressure of the system is lowered to a characteristic point, and the liquid boilsNo heat is supplied to the system, so Hvap is subtracted from the liquidThe temperature of the liquid will decrease, and eventually reach its freezing pointAll three states of matter coexist:

Solid Liquid GasCritical PointIn high pressure and temperature conditions, a substance will enter a state called the critical pointNo phase boundaries existProperties of both liquids and gasesie. Supercritical CO2As pressure and temperature vary, substances behave as expected.Phase DiagramsShows regions of stability of different phases as a function of T and P.

ObjectiveTo determine the triple point of t-butanol and construct a phase diagramEquipment List15mL of t-Butanol + boiling chipsRubber stopper with alcohol thermometer Aspirator/VacuumVacuum gaugeVenting valveHot plateIce bathSuction flaskApparatus

The ExperimentPart A Determining the Multiple Boiling PointsPart B Determining the Multiple Melting Points Part C Determining the Triple PointDetermining the Triple PointThe pressure of the flask is adjusted to 0.056atm with the aspiratorThe t-butanol will start to boil, and vaporizing particles will extract Hvap from the liquid, causing it to cool.

Results

Tert-butyl alcohol:BP: 82-83C, 1atmMP:25-26C, atmTP:25.6C, 0.056atmResultsHvap can be determined from the slope of the line of log(P) vs 1/T:

ResultsSvap can be calculated from:

Applications of Triple PointsThermometer CalibrationRelevanceThermodynamicsPhase diagramsBetter understanding of phase changesDifferent internal and external pressuresUnderstanding of H and SPros and ConsProsShort lab, ~10 minutes/trialInexpensive ($56.30/100mL for t-butanol)Simple procedureNot so much mathConsTert-butyl alcohol is flammable and an irritant to the skinVideohttp://www.youtube.com/watch?v=BLRqpJN9zeAQuestions?ReferencesResearch:http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/phase.phphttp://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/State_Functions/Enthalpy

Lab: http://www.collin.edu/chemistry/Handouts/1412/Phase%20diagram01-14-11%20pilot%20run%20spring%202001.pdfhttp://www.avs.org/AVS/files/0d/0dfcada7-2627-447c-91bc-eba402394ac6.pdf