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Unformatted text preview: Experiment 15: Standardiza2on of NaOH • Key Terms • Titra2on: Quan2ta2ve chemical analysis technique. Used to determine the quan2ty of analyte (NaOH) in solu2on. • Buret: An instrument used to do 2tra2ons. It allows us to accurately dispense volumes of liquids. Record volumes to 4 signiﬁcant ﬁgures (ex: 28.54mL) • Titrant: The solu2on dispensed out of the buret. • Equivalence Point: The point in the 2tra2on when all of the acid (KHP) in the ﬂask has reacted with base 2trant (NaOH). Key Terms • Colorimetric Indicator: A compound that changes color once the equivalence point has been reached. Phenolphthalein is the indicator in this experiment. • Endpoint: The point where the indicator tells you that the equivalence point has been reached. You will record the volumes needed to reach the endpoint. This 2tra2on is carried out to a phenolphthalein endpoint. • Primary Standard: The acid (KHP) that is reacted with NaOH is a primary standard. See the lab manual for a detailed descrip2on of the characteris2cs of primary standards. • KHP: Abbrevia2on for potassium hydrogen phthalate. A commonly used primary standard with one acidic hydrogen. KHP reacts with NaOH in a 1:1 ra/o (similar to HCl reac2ng with NaOH). • Neutraliza2on reac2on: A base reacts with an acid to produce water and an ionic salt. KHP (an acid) neutralizes NaOH (a base) in this 2tra2on. Techniques: Solu2on Prepara2on • Preparing solu2ons is just like solving dilu2on problems. moles
• Watch your units. Molarity (M) is in Liter
• Use the formula: MiVi=MfVf , where Mi= ini2al NaOH molarity Vi = ini2al NaOH volume (solve for this) € Mf = ﬁnal NaOH molarity a^er dilu2on Vf = Final volume of diluted NaOH Solu2on Prepara2on Sample Calcula2on • What volume of the 5.0M stock solu2on of NaOH should be used to prepare 0.5L of 0.1M NaOH solu2on? • MiVi=MfVf i
• Mi= 5.0M Vi = Solve for this. Mf =0.1M i Vf = 0.5L (5.0M)(V ) = (0.1M)(0.5L)
(5.0M) € Weighing by Diﬀerence • This is the most accurate method to obtain a mass of a substance. • 1. Weight the bodle containing KHP (ex. 25.754g) • 2. Carefully pour out some KHP into your Erlenmeyer ﬂask. • 3. Weigh the bodle containing KHP again (25.554g). • Mass of KHP added = Ini2al Bodle Mass – Final Bodle Mass 25.754g − 25.554g = 0.200gKHP € Titra2ons • Do not rush your 2tra2on. • The solu2on will turn pink as NaOH is added, and then it will become clear again. • As you approach the endpoint, the pink color will persist longer. • At the endpoint, the solu2on in the ﬂask should be a faint pink. € Sample Titra2on Calcula2on Data Needed: Mass of KHP in solu2on MW of KHP: 204.23g/mol Volume (L) of NaOH dispensed (Endpoint Volume). gKHP × 1molKHP
= M _ NaOH
204.23g EndpointVolume 0.6000g × 1mol
= 0.1034 M
204.23g 0.02841L ...
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- Spring '07