CHM211H5 Chapter Notes - Chapter 4: Potassium Hydrogen Phthalate, Potentiometric Titration, Sodium Hydroxide
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Experiment 4: potentiometric titration of phosphoric acid mixtures. The unknown is composed of between 0. 06 and 0. 08 m h3po4 plus hcl or nah2po4. Khp is available from the desiccators next to the balances. Accurately weigh by difference one such sample into a 250 ml erlenmeyer flask and dissolve in 50 - 75 ml of distilled water; swirl until the solid is all dissolved. Mol khp= mol naoh=c v =0. 15m 0. 030l=4. 5 10 3 mol mass khp=4. 5 10 3 mol 204. 22g mol. Mol khp=0. 15m 0. 035l=5. 25 10 3mol mass khp=5. 25 10 3mol 204. 22g mol. =1. 07g: add 3 - 4 drops of phenolphthalein indicator and titrate with the 0. 15 m naoh to the first faint pink colour that persists for 30 seconds. This sample should be used to perform a fast titration in order to establish the approximate endpoint and the colour change: weigh out three more (separate) khp samples one at a time.
