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Experiment 9 Overview, Lecture notes of Chemistry

University of British ColumbiaChemistry

Experiment 9 overview for the lab (Chem 123)

Typology: Lecture notes

2021/2022

Uploaded on 08/09/2023

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E x p e r i m e n t 9 O v e r v i e w P a g e | 1
EXPERIMENT 9
Chemical and Nutritional Aspects of Vitamin C: A Project
PRE-LAB REQUIREMENTS
PRE-LAB REQUIREMENTS FOR EXPERIMENT 9 ARE…...
1.
Read the experiment up to the Lab Project Summary section:
• Pay careful attention to the description of the experimental design process.
2.
Formulate a Hypothesis and Research Question:
• Write these down on the cover page of your EDF.
3.
Research a Literature Article for your Project:
• Chose an article that corresponds to the research question of your experiment.
4.
Read the rest of the experiment:
• Start to design your procedure.
5.
Read the Experimental resources:
• Become familiar with the techniques used in the experiment by working through the
following resources:
Techniques
• Iodometric Titration
The following tutorials are a refresher from CHEM 111/115/121
• Weighing Objects
• Significant Figures/Volumetric Analysis
• Standard Solution
Virtual Lab – Iodometric Titrations:
• Use the Experiment 9 Virtual Lab: Iodometric Titration -Preparation of a KIO3
Standard Solution to help design your experiment and assist you with calculations.
This is for your own reference and does not need to be submitted.
6.
Complete the Pre-lab Quiz (in Canvas)
This quiz must be completed BEFORE the start of your Experiment 9 lab session
7.
Complete the Pre-lab portion of the Experimental Design Form:
As you design your procedure and complete the EDF (in pen):
• Use the Experimental Overview and Virtual Lab Tutorial to assist with designing your
procedure
• As you read through the Experimental Overview, choose glassware, equipment and
chemicals for each step from the Laboratory Stockroom
• Calculate the mass of KIO3 your project requires
Note:
You will discuss the validity of your project with your TA during the check-in week
Do not attempt to leave all of the above work until the last minute.
You will be overwhelmed and poorly prepared for the lab if you do.
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EXPERIMENT 9

Chemical and Nutritional Aspects of Vitamin C: A Project

PRE-LAB REQUIREMENTS

PRE-LAB REQUIREMENTS FOR EXPERIMENT 9 ARE…...

1. Read the experiment up to the Lab Project Summary section:

  • Pay careful attention to the description of the experimental design process.

2. Formulate a Hypothesis and^ Research Question:

  • Write these down on the cover page of your EDF.

3. Research^ a Literature Article for your Project:

  • Chose an article that corresponds to the research question of your experiment.

4. Read the rest of the experiment:

  • Start to design your procedure.

5. Read the^ Experimental resources:

  • Become familiar with the techniques used in the experiment by working through the

following resources :

Techniques

  • Iodometric Titration The following tutorials are a refresher from CHEM 111/ 115 /
  • Weighing Objects
  • Significant Figures/Volumetric Analysis
  • Standard Solution Virtual Lab – Iodometric Titrations:
  • Use the Experiment 9 Virtual Lab: Iodometric Titration - Preparation of a KIO 3 Standard Solution to help design your experiment and assist you with calculations. This is for your own reference and does not need to be submitted.

6. Complete^ the Pre-lab Quiz (in Canvas)

This quiz must be completed BEFORE the start of your Experiment 9 lab session

7. Complete the^ Pre-lab portion of the^ Experimental Design Form:

As you design your procedure and complete the EDF ( in pen ):

  • Use the Experimental Overview and Virtual Lab Tutorial to assist with designing your procedure
  • As you read through the Experimental Overview, choose glassware, equipment and chemicals for each step from the Laboratory Stockroom
  • Calculate the mass of KIO 3 your project requires Note: You will discuss the validity of your project with your TA during the check-in week

Do not attempt to leave all of the above work until the last minute.

You will be overwhelmed and poorly prepared for the lab if you do.

A. Basic laboratory skills A1. Adhere to instructions on laboratory safety, recognize hazardous situations, and act appropriately. (Refer to A1.b in the General Laboratory Learning Goals (LGs).) A1.a : General safety: Follow relevant safety practices required for your chosen experiment and sample preparation. A2. Perform common laboratory procedures correctly. (Refer to A2.b & c in the General Laboratory LGs.) A2.a : New laboratory procedures

  • Set up a control o Explain the purpose of a control and identify a control for a simple experiment
  • Prepare samples appropriately for analysis (apply lab manual guidelines) o Consider the amount of analyte in each sample versus the control amount o Consider the minimum amounts of analyte needed to perform iodometric titration
  • Perform iodometric titration o List the general procedural steps of a titration
  • Use (as appropriate) microwave, UV lamp, pH meter. A3. Maintain an up-to-date laboratory record that is of sufficient detail that others could repeat any of your experiments if necessary. (Refer to A3 a, b & c in the General Laboratory LGs.) A4. Apply appropriate methods of analysis to data and convert raw data into meaningful units.
  • Record the amount of Vitamin C in the control and treated samples with meaningful units
  • Calculate the concentrations of ascorbic acid solutions from data
  • Calculate the amount of Vitamin C in each sample
  • Compare analyte amounts in the control versus the treated samples A5. Perform logical troubleshooting of laboratory procedures.
  • Consider the time needed for preparation in addition to the time needed to perform titrations
  • Adjust the concentration of the standard solution to enable titration of samples within a volume range that will provide results with the maximum number of significant figures o Diagnose/remedy failure to reach endpoint
  • Determine how to maintain a reasonably constant temperature when using a hotplate
  • Recognize when it is needed and how to make adjustments for evaporation.
  • Use a protocol to ensure uniform reading of the endpoint B. Communication (Refer to B1 & B2 in the General Laboratory LGs.) B3. Access (and properly cite) relevant information from the library and other resources. Access one or two relevant scientific articles for your chosen investigation of Vitamin C degradation in foodstuff C. Responsibility (Refer to C2 in the General Laboratory LGs.) C1. Effectively prepare in advance for laboratory work.
  • Complete the online tutorials and the virtual lab on iodometric titration in advance of wet lab
  • Recognize the factors that accelerate Vitamin C degradation in foodstuffs D. Context D1. Use the scientific method.
  • Develop a research question about the degradation of vitamin C with the appropriate number of variables explored
  • Develop a reasonable hypothesis for the above research question based on lab manual guidelines and literature research
  • Develop an appropriate experimental design to test your hypothesis
  • Make evidence/data based conclusions about the results of your experiment
  • Evaluate experimental results in relation to the hypothesis and account for errors D2. Describe what your data does and does not say.
  • Interpret the data o Consider the limitations of the experiment (ex: iodometric titration endpoint precision and accuracy) o Consider the limitations of the instruments (ex: decimal places given by the balance) E. Integration and application of knowledge/experience E1. Apply critical thinking to the experiment.
  • Extract information from a journal article
  • Describe the value of using a control and the purpose and value of repeating tests (such as titrations) E2. Recognize whether results and conclusions "make sense". Examples of questions to consider:
  • Do the experimental results “fit” with the reported amounts of Vitamin C in your sample?
  • Was Vitamin C “lost” or “gained” as the variable(s) changed?
  • Do the results of your experiment fit logically with information in the lab materials and scientific literature? EXPERIMENT #9 LABORATORY LEARNING GOALS Read through the learning goals for Experiment 9 below.

The Experiment

LAB PROJECT SUMMARY

These aspects of the experiment are described on the following page:

  1. Goal of the Experiment.
  2. Designing a Vitamin C Project.
  3. Reading Literature on your Project.
  4. Theory of Iodometric Titration.
  5. Experimental: How to Perform an Iodometric Titration. 1. Goal of the Experiment The goal of the project is to give you an opportunity to independently design and perform a scientific study on some aspect of vitamin C decomposition. The vitamin C experiment consists of pre-lab material/assignments designed to familiarize you with the necessary laboratory techniques and concepts to help you prepare a project that will be investigated in the subsequent in-lab session. 2. Designing a Vitamin C Project As already mentioned, there are many different variables that affect the rate of vitamin C (ascorbic acid) degradation:
  • Presence of oxygen
  • Temperature
  • Presence of metal ions (transition metals)
    • pH
    • Light (mainly UV)
    • Presence of enzymes (not offered in the lab) These variables could lead to any one of the possible project topics listed below. You can decide which vitamin C source to choose from: orange juice, cranberry juice, apple juice, ascorbic acid solution and Vitamin C tablets.
  • Study of some of the factors that are important in vitamin C decomposition, particularly the presence of Cu2+^ or Fe3+, heat, and pH.
  • Examine the effects of various cooking methods (baking, boiling, steaming, microwaving) on the vitamin C content of your sample.
  • Study the factors that control decomposition of vitamin C in stored fruit juices. The variables may include time, temperature, light, type of juice and pH. Once you have decided on a research topic, you can start to design your project. Let’s say you have decided to investigate the effect of temperature on the decomposition of vitamin C. Some background knowledge of chemistry leads you to expect that increasing temperature will increase the rate of ascorbic acid oxidation, and therefore decreasing the amount of vitamin C present. You would start by asking a viable research question. An example research question: “What will happen to the vitamin C content in a piece of orange if it is heated to 50oC, 75oC and 100oC?”

As we have already mentioned above that temperature is a factor in the degradation of vitamin C, you might feel fairly confident in formulating a hypothesis (the statement that you will test with your project) at this stage. An example Hypothesis : “The vitamin C content in a piece of orange will decrease as the temperature of the sample is increased.” Remember, that according to the scientific method, you can never prove a hypothesis. Your results can either:

  • support (validate) the hypothesis when they agree with the statement, or
  • disprove (refute) the hypothesis if they do not agree with it If your results do not agree with your hypothesis, this does not mean that your results are of no value. You can learn as much from an unexpected result as you can from an expected one. If things do not turn out as you predicted, you should try to think about what led to the results that you obtained. Once you have decided on a research question and formulated a hypothesis, you must test your hypothesis by performing an experiment. Testing of the validity of your hypothesis, is what will be accomplished during your lab. You are required to consult the literature before designing your project (see point 3 “Reading Literature on your Project”). When designing an experiment to test your hypothesis, keep the following important factors in mind:
  • Necessity of having a Control It is necessary to have a control sample to act as a standard of comparison. The control needs to be subjected to the exact same conditions as your experimental sample, except for the single condition (variable) that is being tested in the experiment. This allows you to determine the effect of changing the single variable. For example, a study of the decomposition of vitamin C during cooking in a copper pot may involve the following: a. Pure ascorbic acid is boiled in water for 10 minutes. No copper is used. This solution is the control sample to determine the effect of copper on the boiling of ascorbic acid. It is not a control allowing one to determine the effects of both temperature and the presence of copper. b. Pure ascorbic acid, water, and a strip of copper metal are placed in a beaker. The mixture is boiled for 10 minutes to simulate cooking in a copper pot. This is the test sample.
  • Naturally Occurring Amounts of Vitamin C in Foodstuffs
  • Vitamin C amounts in your samples will be determined via an iodometric titration. This technique only works well down to a level of approximately 5 mg of vitamin C per sample. Make sure there is at least this amount of Vitamin C in each of your samples.
  • Click here for information on various fruits and vegetables. Milk is the only animal product containing vitamin C in significant amounts (1 - 5 mg per 100g), but we do not recommend examining it since an iodometric titration is very difficult with milk.
  • For packaged juices or foodstuffs, check the Nutrition Label on the packaging for Vitamin C levels. See here how to use the label to calculate the amount of Vitamin C in the product.
  • The Recommended Daily Aloowance (RDA) for Vitamin C (adults) in Canada is 90 mg.
  • Reproducibility of your Results To ensure reproducible results, each sample should be titrated at least twice. This limits the number of different samples you will be able to examine in the laboratory period.
  • Extra Equipment and Chemicals Available Extra equipment available especially for Experiment 9 are listed in the Laboratory Stockroom.

Preparing samples Issues Time A student is expected to:

  • Prepare a standard solution of KIO 3
  • Prepare samples (2 for the control and at least 4 test ones)
  • Expose samples to the variable
  • perform 6 titrations during the experiment:
    • 2 on the control
    • 2 on a sample exposed to the variable (eg 10 minutes at 100 0 C)
    • 2 on a sample exposed to the variable (eg 20 minutes at 100 0 C) Preparing samples Issues Using solid foodstuff If you decide to use asolid food item, such as a fruit or vegetable you have to keep the following in mind:
  • You may spend a lot of the lab preparing your item. Your sample needs to be in liquid form to be able to pipet for the titration o need to extract the juice from the fruit – squeezing / blending o vegetables you may need to chop them fine and then blend with water to get a liquid to test
  • liquids that contain solid matter are hard to pipet (it gets clogged) **Note: If you choose to analyze apple juice, add 7.5 mL of EDTA per 100 g (100 mL) of sample to prevent the Fe or Cu ions from interfering with your project.
  1. Finding Literature on your Project Why Consult the Literature?** Once you have formulated your hypothesis, you must consult the research literature to see if other scientists have already investigated the same topic. This can be of great value, as the prior work of others can help guide your own work. In many cases, the literature found during this search should let you anticipate the answer to your research question. You might even want to revise your hypothesis, project, or both, after consulting the literature. How to Consult the Literature? For Experiment 9 the library search has been done for you and the articles posted in the “Library Research” module of Experiment 9. What to do with the Literature? Support the rationale of your hypothesis/project by concisely describing the work of the article(s). This description will be done in the Introduction portion of your Lab Report. How to Write an Introduction? A “Sample Introduction” can be found in the “Writing a Lab Report” module in the Course Info. We know that you probably do not currently have much experience using articles. A practice assignment has been designed to help you learn how to extract the important information from a research article, and then summarize this compiled information in a concise paragraph. This is in the Course Resources module “Guidelines to Reading Articles” in Canvas.

4. Theory of Iodometric Titration

  • Determination of Ascorbic Acid Concentration via Redox Titration with Potassium Iodate A suitable method for the determination of vitamin C (C 6 H 8 O 6 ) is a titration with potassium iodate (KIO 3 ). Potassium iodate is used as a titrant and is added to an ascorbic acid solution that contains strong acid and potassium iodide (KI). Potassium iodate reacts with potassium iodide, liberating molecular iodine (I 2 ): KIO 3 + 5KI + 6H+^ → 3I 2 + 6K+^ + 3H 2 O (1) As long as the solution contains ascorbic acid, the I 2 produced in equation 1 is used up in a rapid reaction with ascorbic acid (equation 2), during which dehydroascorbic acid (C 6 H 6 O 6 ) and iodide ion (I-) are formed: C 6 H 8 O 6 + I 2 → C 6 H 6 O 6 + 2I-^ + 2H+^ (2) Potassium iodide must be added in excess to keep iodine dissolved. Once all the ascorbic acid has been consumed, any excess iodine will remain in solution. Since aqueous iodine solutions are brown in colour, iodine can act as its own indicator. However, it is quite difficult to detect endpoints using iodine colouration alone, and it is more usual to add starch, which forms an intensely blue coloured complex with iodine but not with the iodide ion. According to the above equations, each mole of potassium iodate added corresponds to 3 moles of ascorbic acid dehydrogenated in the sample.
  • General Procedure of Iodometric Titration In the redox titration of vitamin C with potassium iodate, the KIO 3 solution serves as a primary standard, and is therefore carefully prepared in a volumetric flask. The KIO 3 standard solution is then used as a titrant and added from a buret to a liquid sample containing ascorbic acid (Vitamin C). Starch, excess KI, and HCl (to supply H+) must be added to the sample before the titration begins. As discussed above, once all of the ascorbic acid has been converted to dehydroascorbic acid, iodine remains in solution and forms a deep blue complex with the starch, signaling the endpoint of the titration. To maintain 4 significant figures in your measurements, the titration must use at least 10.00 mL of KIO 3. However, to minimize the impact of slight errors in correctly reading the buret, it is usually recommended to use 25 mL of a titrant. As the amounts of vitamin C present in food samples can be quite small (< mg), a very dilute solution of KIO 3 must be prepared. For example, a 0.0100 M solution of KIO 3 is far too concentrated since less than 2 mL are required to completely titrate 10 mg of ascorbic acid. To get a rough idea of what concentration of KIO 3 we will need for our titrant, we will approach the problem “backwards” by assuming a given amount of vitamin C in our sample and then determining an appropriate KIO 3 concentration, to titrate the sample with about 25 mL of it. Note that in your experiment, you will first make a KIO 3 solution of a known concentration and then analyze your experiment’s titration data by working in the “forward” direction to calculate the amount of vitamin C in your sample. The Virtual Lab tutorial for Experiment 9 will lead you through the “backwards” calculation. The Virtual Lab interactive activity is available for you to test your design of this project.
  • Estimate how many milligrams of ascorbic acid will be present in your project’s samples Calculate the mass of KIO 3 required to make your standard solution. Include the calculation on your EDF (Part 1). Your TA will check the amount and notify you of any corrections needed. Typical ranges of KIO 3 are 0.01 – 0.4 grams. You can confirm your calculated mass by completing a Virtual Lab simulated titration. If you weigh out less than 0.1 grams of KIO 3 in the lab, the analytical balance can only give you 3 significant figures. Consider how this might affect your results.

PRE-LAB CHECKLIST Make sure to do the following before you perform the experiment:

❑ Read through all^ the^ components of the experiment

❑ Formulate a^ research question and hypothesis

❑ Chose^ an article relevant to your project

View the Technique: Iodometric Titration and Experiment 9 Virtual Lab: Iodometric Titration - Preparation of a KIO 3 Standard Solution

❑ Complete the^ Pre-lab Quiz^ (see deadlines below)

Complete IN PEN the pre-lab part of the EDF listed below,

  • Research question and Hypothesis
  • Glassware / equipment and reagents needed
  • Calculation for the amount of KIO 3 solid needed to prepare your standard solution
  • Procedure - Remember, keep it concise. If you want to bring in additional notes for your own reference, that is ok, but do not include them in your EDF. The more you prepare for the wet lab the easier your experiment will seem. Familiarize yourself with:
  • your own procedure so you are aware of the order the experimental steps are performed
  • any techniques in the experiment
  • calculations you will need to complete to analyze your data to gain results SUBMISSION DEADLINE Task Submit (material) Submit / complete (when) Prepare for lab:
  • Read experimental overview
  • Read online material
  • Find research article Pre-lab Quiz Quiz Submit before the start of your Experiment 9 lab session* Submit in Canvas Complete pre-lab portion of EDF Complete before the start of your Experiment 9 lab session* Submit with your lab report Complete in-lab portion of EDF EDF Complete before the end of your Experiment 9 lab session* Submit with your lab report Complete Lab Report Lab Report Submit at your next lab session *No late submissions **Late penalties apply (2 marks deducted per hour after the deadline)