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Lab 5: What is the Weak Acid?TA: James GeigerGroup 3Introduction:
The main goals of this two part lab are to understand basic ideas andcharacteristics of weak versus strong acids. In part I standardization ofNaOH is carriedout using the acidic salt, KHP. During this experiment it is important to know how todetect an endpoint as well as having the ability to calculate molarity. The goal of part IIof the lab is to take an unknown weak acid and use our understanding of pH meters andtitration curves in order to determine the equivalence point, molarity and Ka value.A titration is a process used to neutralize an acid-base reaction. A titrant (NaOH)is slowly added to a solution of known volume until the indicator (phenolphthalein) isobserved indicating the endpoint.In this experiment the pH meter was used as a technique to determine the pHlevel.The equivalence point is reached when the moles of acid and moles of base areequal. In the lab the equivalence point is determined using the titration curve.Experimental:Part 1: Standardization of NaOHMaterials:●50 mL Buret●Buret Stand●Hot plate
●(3) 250 mL beakers or flasks●(1) 125 mL beaker of boiled DI water●NaOH●(3) ~ 0.5g samples of solid KHP●1% phenolphthaleinMethods:The buret was cleaned and calibrated by prior classes, so it was already primed withNaOH, the volume was recorded;(4.0mL) and buret was placed on the stand. The KHPwas obtained and weighed around 0.28 grams. We then placed the KHP in a 250mLbeaker.The DI water was boiled to ensure that no CO2 is present in the water, as thiswould throw off the pH reading. The beaker was filled with 50mL of boiled DI water and2-3 drops of the 1% phenolphthalein indicator; this solution is then stirred on the hotplate until all the KHP is dissolved. Once dissolved, the solution and hot plate is placedunder the buret and ready for titration to begin; we also made sure there were nobubbles at the tip of the buret. Slowly, the stopcock was opened and the NaOH wasreleased to turn the solution to a very faint pink color which will indicate the endpoint.