CHEMLABexam2

CHEMLABexam2 - CHEMLAB 17:22 LAB 6 Phospheric acid (H3PO4)...

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CHEMLAB 17:22 LAB 6 Phospheric acid (H3PO4) Sodium hydroxide (NaOH) Methyl Orange (C14H14N3NaO3S) Red to yellow at 4 Phenolphthalein (C20H14O4) colorless to red at 9 Henderson hasselbach If log is – then acid/base If log is + then base/acid When pH=pK then –log(acid/base)=0 and acid/base=1 and buffer solution is  most efficient – half equivalent point pH electrodes – most common are glass, combination electrodes if a pH meter is used everyday, should be calibrated once a week need 2 solutions of known pH, we used 7 and 4 Solution is at equilibrium point when mmol of titrant added = mmol of buffer Endpoint of a titration is when the indicator changes color or when volume or  amount of acid or base added to a solution to neutralize the unknown solution  during a titration  Resonance structures of H3PO4 are why double bonds between the P and O  fluctuate (sometimes it is single) pH electrode is much more accurate than an indicator # of equivalence points = # of dissociating protons PROCEDURE Calibrate pH meter
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Rinse burette with 5mL .1M NaOH first 45mL of .1M NaOH in burette 10mL of H3PO4 and 5 drops of methyl orange immerse electrode record readings in 1 mL increments when methyl orange turns from red to yellow, not point and add 5 drops of  phenolphthalein continue til 30 to 35 mL added repeat rinse electrode between titrations LAB 7 Potassium phosphate (KH2PO4) HCl NaOH Acetic acid CH3COOH Sodium acetate CH3COONa Formic acid HCOOH Sodium Formate NaCOOH Buffer 1 and 2 used Formic and Sodium formate Bufer 3 and 4 used acetic acid and sodium acetate Buffer capacity depends on absolute and relative component concentration
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Henderson Hasselbach pH=pKa + log base/acid buffers use le chatlier’s principle and the common ion effect
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This note was uploaded on 05/02/2011 for the course CHEM 164 taught by Professor Sokic-lazic during the Spring '11 term at Saint Louis.

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CHEMLABexam2 - CHEMLAB 17:22 LAB 6 Phospheric acid (H3PO4)...

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