Post Lab Questions Fall 21 PDF

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post lab questions for the post labs....

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Post Lab Questions Fall 2021 Instructions: Please do not write out the question in your response as Turnitin will flag it and provide an inaccurate plagiarism score. Questions that contain the symbol (¶) are discussion questions and must be answered with longer responses. When using references you must provide proper ACS formatted citations at the end of the question it is used in.

Lab 1: Weighing Procedures and Glassware Calibration 1. Why should you not handle the coins with your finger? 2. Why is it important to measure the temperature of the water before calculating the density? 3. Is the possible to weigh out exactly 0.5000 g on an analytical balance? Reason. 4. (¶) Explain why it is important to rinse the glassware 2-3 times with de-ionized water and with a little portion of the titrant before use. 5. (¶) You are employed as a lab scientist at a culinary company. Your first task is to determine the density of cooking oil. How will you achieve this?

Lab 2: Gravimetric Determination of a Chloride in a Solid Sample 1. What is gravimetric determination? How is this theory applied in this experiment? 2. What steps and conditions (physical, chemical and/or procedural) help in precipitation of silver chloride in this experiment? Explain briefly. 3. Explain the terms: co-precipitation, peptization, and photo-decomposition. Are these phenomena witnessed in this experiment? If detrimental, what precautions were taken in the experiment? 4. (¶) Why are Gooch funnels used for gravimetric analysis? Are there other types? Which is better? 5. (¶) The precipitative gravimetric analysis finds applications in environmental chemistry for precipitation of sulfates from wastewater. There are different steps and conditions required in such a real-life situation unlike the lab experiment dealing with only chlorides. Perform a literature search and discuss the measures (for example - temperature, pH changes, chemical reactions) taken during wastewater treatment for recovering sulfates and other contaminants. (cite your sources)

Lab 3: Practice Titration: Analysis of a Weak Acid, KHP 1. What is the correct way to handle a burette and an Erlenmeyer flask during a titration? 2. Provide at least 2 different examples of desiccant material and at least 2 different styles of desiccator and explain how they function differently. 3. Why is water boiled prior to the preparation of NaOH standard solution? Explain briefly. 4. (¶) What is standardization in acid-base chemistry? What constitutes a standard in analytical chemistry? Give types and examples. 5. (¶) In the following graph depicting a titration curve for weak acid vs strong base (titrant), explain the chemistry occurring (in regards to chemicals and their states, equilibria)at four points a, b, c, and d indicated.

Lab 4: Volumetric Determination of Impure Sodium Carbonate 1. Why is the HCl standardized and what is does this mean? 2. What is an equivalence point? What is an endpoint? How can you tell when these points have been reached? 3. Why are two indicators used in the experiment? 4. (¶) Explain why the analyte solution is boiled and what occurs during this process. 5. (¶) A popular household product manufacturer, Leg and Screwdriver, produced a batch of baking soda and would like to grade the purity of the product according to the table. In a

titration, equivalence was reached when 38.2mL of 0.3M HCl was added to 1 gram of baking soda. What grade was this batch found to be? How were you able to make this determination?

wt% >99.9% >99% >97% >95%

Grade Reagent Lab Food Technical

Lab 5: Iodometric Determination of Sodium Thiosulfate 1. Why is it important to start the titration soon after adding KI? 2. What produces the yellow color before the titration? 3. In this experiment, what starch indicator complex plays a significant role in identifying the extent of the titration? How? 4.

(¶) Explain the role of each reagent in this titration.

5. (¶) Iodometry is a general method used to determine the concentration of an oxidizing agent in a solution. Design an iodometric experiment to determine the concentration of hydrogen peroxide in a sample. Provide all chemical reactions and experimental parameters.

Lab 6: Determination of Ascorbic Acid in Vitamin C Tablets 1. (¶) In the production of any pharmaceutical drugs, there are strict quality control rules that must be met before a product can be sold to a consumer. Supplements, on the other hand, are not as strictly regulated and have had several major incidents of placebo pills or adulterated pills being sold to the public. Perform a literature search on the study of falsified dietary supplement pills and discuss a single article in detail. The article must come from a scientific journal such as “Comprehensive Reviews in Food Science and Food Safety” and not a website. 2. Define what a back-titration is and provide a reason why this method is more suited for this reaction than a direct titration. 3. Before the first titration is performed you must mix the ascorbic acid powder sample with 1.5 M H2SO4 and KBr. What role do these reagents play in this initial mixing?

4. After reaching the final titration endpoint the solution will be cloudy white. As time goes on the solution will turn back to a cloudy dark purple color. Why does this occur if you have already reached the endpoint? 5. (¶) What is the difference between percent composition and percent recovery? Which of the two are you finding in this experiment?

Lab 7: Spectrophotometric Determination of Iron in Mohr’s Salt using Ophenanthroline 1. Equation of Beer-Lambert’s law and explain all values. Also, how to determine transmittance (%T) from Beer-Lambert’s law? 2. What is the purpose of the acid added in the beginning? 3. What is the purpose of hydroxylamine hydrochloride in this experiment and why was this important? 4. (¶) Why is the reagent-blank necessary? 5. (¶) The reaction Fe2+ + 2H2O –Fe(OH)2 + H+ occurs readily. Why would this be a problem in the determination of the amount of iron? What procedure was used in this experiment to prevent this reaction from interfering with the determination of the percent iron in the unknown sample?

Lab 8: Determination of pka of Bromocresol Green 1. (¶) Based on the color observations, what PH range would bromocresol green be an appropriate indicator for? Would this pH range be appropriate for titrations of (a) strong acids by strong bases, (b) weak acids by strong bases, or (c) weak bases by strong acids? Explain. 2. What criteria are used to select a wavelength for measuring absorbances in these solutions? Why? 3. What two properties (one chemical and one physical) combine to make bromcresol green useful as an acidity indicator? 4. (¶) In 1.0 mol/L HCl, what form of bromocresol green, HA or A -, predominates? Explain. 5. What single error would have the greatest effect on the accuracy of the experimental results? ¶ - indicates a comprehensive question.

Lab 9: Gas Chromatography: Blood Alcohol Content (BAC) Analysis 1. (¶) Provide a component diagram sketch of a typical gas chromatography instrument setup and discuss the importance of each component. 2. What is an internal standard and how is it utilized? 3. Describe how an FID detector and one other commonly used detector operate and what type of analytes they are useful for detecting. 4. In a calibration curve, you obtain the best fit line and R 2 value. What does the R2 value tell you about your data? 5. (¶) In the context of this experiment, GC is used for forensic analysis but is applicable to many other fields. Perform a literature search for new advancements in GC techniques. Referencing one paper, summarize the work and make sure to provide proper ACS citations.

Lab 10: Gas Chromatography: Essential Oil (EO) Analysis 1. Describe the characteristics of the column used in this experiment (eg. Chemical composition, temperature limits, suitable compounds to analyze, etc…). 2. (¶)What is column bleed and what steps can be taken to minimize it? 3.

What are the advantages of using the standard addition calibration method over the external calibration method?

4. (¶) When performing a liquid injection onto a GC system what considerations regarding the sample must be made to ensure efficient chromatography? 5. Utilizing the external calibrations method, is it possible to extrapolate beyond the calibrated solutions and describe why or why not?...