You will undoubtedly note towards the end of the

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Chapter 27 / Exercise 8
Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems
Bennett
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Many people are confused by the color changes in this titration. You will undoubtedly notetowards the end of the titration that when you are adding the NaOH very rapidly and not swirlingfast, some pink color develops very close to where the stream of NaOH enters the solution. Thishappens because mixing is not fast enough and locally there is more NaOH than acid. Furthermixing rapidly removes the pink if there is an excess of acid in the flask. We call this “localtitration.” It is a sign that you are getting close to the endpoint.As soon as there is really a slight excess of NaOH relative to acid in the whole flask, the entireflask will turn very, very light pink (not red). This is the real endpoint. This pink may persist forabout one minute as you continue to swirl the flask. It will fade very slowly because the labatmosphere contains a weak acid (CO2), which gradually dissolves in the flask, reacts with slightexcess of NaOH present at the phenolphthalein endpoint, and causes the pH to drop below the pHwhere phenolphthalein in pink. You must repeatthe titration until you have three trials with aprecision of 0.2 %or lesswith respect to the mean.[NaOH]ave[NaOH]ave0.2 %[NaOH]nx 100%where nrefers to any of the three trials.
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Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems
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Chapter 27 / Exercise 8
Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems
Bennett
Expert Verified
III. Waste Disposal: Neutralize the acids and the bases used in this lab with one another first. Ifacids remain in excess, neutralize them with sodium carbonate (Na2CO3). If bases remain inexcess, neutralize them with 6 M HCl. Make sure, with a piece of pH paper, that the final solutionpH is in the range of 5 to 9 before pouring it down to the drain. CHM3120C Analytical Chemistry Lab Lab 3. Practice Titration, Potassium Hydrogen Phthalate (KHP)
Name:_______________________ Section: AllID #: _______________________ Lab ReportPart 1: Preparation of 0.1 M carbonate-free NaOH solution, and drying KHP. Part 2: Titration (Standardization of NaOH solution)Trial 1Trial 2Trial 3Mass of a weighing paper (or dish)Mass of a weighing paper (or dish) anddried KHPMass of dried KHP# of moles, KHPVolume of NaOH (Initial buret reading)Volume of NaOH (Final buret reading)Volume of NaOH used Molarity of the NaOH solution% ErrorAverage Molarityof the NaOH solution and STD:______________________________*After finishing “Part 2”, you must turn in the “Lab 3 Report” before you leave.*Note 1: Make sure to include all the experimental data with proper units, and significantnumbers.*Note 2: There will be 10% penalty for the late report.Do not write below this line.---------------------------------------------------------------------------------------------------------------------Grade: _____________________CHM3120C Analytical Chemistry Lab Lab 4. Volumetric Determination of Impure Sodium Carbonate (Na2CO3)
**Required Reagents and Supplies (for 1 section or 14 people): minimum 12 g of dried sodaash (unknowns), phenolphthalein indicator, bromocresol green indicator, minimum 1 L ofstandardized HCl (~ 0.12 M), 200 mL of 6 M HCl solution, and the pH paper.I. Introduction:In this lab, you will be using the standardized solution of HCl to titrate asolution of unrefined sodium carbonate (Na2CO3, MW: 105.989 g/mol) known as “soda ash.” Byknowing the amount of soda ash that is titrated, and the volume of standardized acid used, youmay determine how much total carbonate is actually in the sample.

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