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LBS_172L_Students-_KD - Partition Constant of an Partition...

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Unformatted text preview: Partition Constant of an Partition Constant of an Organic Acid Week of February 2, 2009 General Guidelines General Guidelines • Do not pipette from stock bottle – Pour liquid in small beaker and then take from this – Do not return excess liquid to stock container as this leads to contamination • DO not leave dirty glassware in the lab. Wash all glassware after use • Wipe up all spills as they occur Waste Waste • • • NaOH­ down the drain Salicylic acid – waste container Octanol­ waste container KD • When a soluble material (solute) is present in a system which contains two immiscible solvents, A and B, it will distribute itself between them and eventually reach equilibrium Solute A ⇔ SoluteB [Solute A ] KD = [ SoluteB ] [ salicylic acid octanol ] Kow = [ salicylic acid water ] [ ] − molar concentration Kow a special case of KD Kow a special case of K • Why KD? – How organic molecules distribute themselves between water and natural solids (biota, soils, sediment etc) predictable and can be viewed as a partitioning process between two different aqueous phase and bulk organic phase… Environmental organic Chemistry, Schwarzenbach et al. • Why Octanol Kow Kow – Amphiphilic in nature (containing both hydrophobic and hydrophilic properties) – Historically a good surrogate for organisms with respective to accumulation of pharmaceuticals – Also true for other naturally occurring organic phases OH Important this week Important this week • Chemical Concept • Laboratory skills – Intermolecular Forces – Titration – Practice titration skills • End point (only slightly pink!) No bright colors! – Use of separatory funnel Questions to ponder Questions to ponder • Make a prediction about the magnitude of the partition constant (should it be greater than, equal to, or less than 1); provide a reason for your prediction. Note, you may want to consider the polarity of the different molecules involved. When you mix the octanol and water, 2 layers will form. Which layer (octanol or water) should be on top? Why? • Answer to turn in Answer to turn in • What information will be necessary to determine the molecular weight of salicylic acid from your titration?—hint be sure to collect this data. This week This week • Will work in pair – Each person in a group will do separate partitioning ( If 3 people 3 different partitioning!) – Will do titration together – Will be provided with standardization of base information Report Report • Formal in Pairs – Write report without editing – Edit report – Turn in both editions • Must include references! ...
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