Laboratory Topics PERFORMANCE TASKS

PERFORMANCE TASKS After the completion of the first four units of study, you must perform a lab investigation based Performance Task. You are to work ...
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PERFORMANCE TASKS After the completion of the first four units of study, you must perform a lab investigation based Performance Task. You are to work in a group of two or three. Four days of class time will be provided for actual completion of the investigation however each will require a varying degree of preliminary research on your part. A group or individual report may be submitted. All resources used in your preliminary and any subsequent research are to be properly referenced in a bibliography. Reports may be hand written provided they are legible, double-spaced and on one side of the page only. Refer to Appendix A4, Lab Reports, in your text for guidance on the format of the report. The reports will be due on the Monday following the allotted lab time. Choose your investigation from the solutions binder available from your teacher or from the file on the Centennial CVI Science Web site. Once you and your partner(s) have declared your choices you may print from the Web site file the lab that you have selected. The sooner you make your choices, the sooner you can begin the necessary preliminary research and the less pressured you will be as performance time approaches. Choices must be made no later than the last day of Unit 4.

Laboratory Topics 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Chemistry 11 - Nelson - Unit 3 Analysis of ASA (Pg. 406-407) Solubility of Group I Chlorides Determining the Concentration of a Diprotic Acid The Dreaded Eight-Bottle Problem Water Testing Acid Indigestion And Antacid Effectiveness Reaction of Metal Nitrates with Sodium Hydroxide. Analysis of Vitamin C Analyzing a Mixture using Stoichiometry Moisture Content of Popcorn - Statistical Analysis

Last Revised 1/11/10

SOLUBILITY OF GROUP I CHLORIDES INTRODUCTION: 1. What three processes occur when an ionic salt dissolves in water? 2. In terms of these three processes, what allows for increased solubility? 3. The Group 1 chlorides (including LiCl, NaCl, and KCl) have different solubilities, but these salts are related to each other. Why are the solubilities different from each other? How are they related? 4. Find the given solubilities of the Group 1 chlorides and create a solubility graph. PURPOSE: You will experimentally determine the solubility for LiCl, NaCl and KCl and compare with the accepted value. Using these and reference data for the remaining alkali metals, the relationship for their solubilities will be examined and discussed. PROCEDURE: 1. 2. 3. 4. 5. 6. 7. 8.

Measuring 50.0 mL of distilled water into the beaker. Add the salt in small portions with stirring until no more will dissolve. Mass a second beaker. Decant (or filter if necessary) to transfer the solution only into the second beaker. Mass the beaker containing the solution. Mass a watch glass. Place the beaker, cover with watch glass, on a hot plate to evaporate the water. When the water is all gone, mass the beaker, watch glass and residue.

ANALYSIS/DISCUSSION: 1. Determine the solubility of each salt. 2. Determine the % difference for each of the experimentally determined values for the solubility of the different salts 3. Explain any differences in solubility in terms of size of the cations, energy required for bond breaking, and energy released in bond forming. 4. Graph the data and predict the solubility values for the remaining Group 1 chlorides not studied in this experiment.

Last Revised 1/11/10

DETERMINING THE CONCENTRATION OF A DIPROTIC ACID INTRODUCTION: 1. 2. 3. 4. 5.

What is a diprotic acid? Give examples of common diprotic acids. How do diprotic acids behave in water? Describe in detail. Give the Bronsted-Lowry acid-base reaction for a diprotic acid (H2X) dissolving in water. Give the Bronsted-Lowry acid-base reaction for a diprotic acid (H2X) reacting with NaOH. Describe the difference between a strong acid and a weak acid.

PURPOSE: Determine the concentration of a diprotic acid and give determine whether the acid is a strong or weak acid using empirical evidence. PROCEDURE: Hint: Determine the concentration of the standard NaOH solution using a KHP standardization. 1. 2. 3. 4. 5. 6.

Fill a buret with standard sodium hydroxide solution Pipet 25.00 mL of the unknown acid into an Erlenmeyer flask Using pH paper, find the initial pH of the acid. Add 3 drops of phenolphthalein indicator to the acid. Titrate the acid until the solution turns a light pink colour and stays pink for 60 seconds. Repeat this procedure for at least 3 trials.

ANALYSIS/DISCUSSION: 1. 2. 3. 4.

Determine the concentration of the diprotic acid. Is the unknown diprotic acid a strong acid or a weak acid? Explain your answer fully Give a prediction of what diprotic acid that was titrated. Use research to support your prediction. The following graph represents the titration of a diprotic acid with NaOH. Explain why there are two equivalence points. Use chemical reactions to explain what is happening at each equivalence point.

Last Revised 1/11/10

THE DREADED EIGHT-BOTTLE PROBLEM1 Introduction: In this experiment you will be provided with nine different salt solutions, each numbered but otherwise unidentified. All of the solutions are colorless. They are: NaBr, Na2SO4, NH4Cl, NaOH, BaCl2, Na2S, KIO3, Pb(NO3)2. The object of the experiment is to identify each solution, using either the interactions occurring (if any) when small quantities of the solutions are mixed with one another, or any physical evidence. To carry out the experiment successfully, you must obviously know what interactions are expected for each mixture. Intelligent preliminary study is therefore essential. 1. How do most salts exist when in water solutions? 2. When solutions of different salts are mixed, the ionic species present may behave in three distinct ways. What are they? Solubility of salts 3. Define soluble, insoluble, and sparingly soluble. 4. In general what can be said about the solubility of iodates? 5. Why does the more or less soluble Ba(OH)2, often appear insoluble? Other chemical reactions 6. Give balanced equations for the following reactions; (a) Ammonium salts reacting with bases: Sulfide salts reacting with ammonium salts: The reaction of Pb 2+ ions with an initial addition of OH-1 ion followed by an excess of OH-1 (b) Compounds of the iodate ion reacting with compounds of the sulfide ion. In terms of what you will be able to see, there is no difference between elemental sulfur and any other white precipitate. Pre-Lab: 1. Design and prepare a grid structure in which you can predict the results of all possible combinations of the nine provided solutions. 2. Fill it in with P if the reaction represented by a given box is expected to form a precipitate (including sulfur), H2 S if the reaction is expected to produce the gas, NH3 if the reaction is expected to produce ammonia gas, or leave it blank if the mixture is not expected to react. Safety: Describe any chemicals used or their products that have specific hazards associated with them. Identify any hazardous procedures. State all precautions you will take. The Lab: 1. Construct a grid structure in which you can record the results of all possible combinations of the nine provided solutions. 2. Using depression plates and small bellows droppers for this experiment (a) Test all possible combinations of the solutions numbered 1 - 9. (b) Be sure to observe an odour each time you mix two solutions since you will not be able to tell where the odour is coming from if you have more than one mixture on the plastic sheet! Analysis: 1. Identify each of the numbered solutions by comparing your experimental results to the theoretical results. 2. Once you have done this, write a balanced net-ionic equation for each reaction that you observed in the lab. You should have one equation for each reaction marked on the grid [duplicates, if any, need not be written].

1

Adapted from: Ionic Interactions and Qualitative Analysis, Chemical Principles in the Laboratory, 3rd. ed., Robert F. Bryan and Robert S. Boikess Last Revised 1/11/10

WATER TESTING INTRODUCTION: 1. The tests you will perform are confirming tests. That is, if the test is positive it confirms that the ion in question is present. What visible changes to the solution will produce a positive test? 2. Does a negative test mean that the ion is not present? 3. You’ll perform each confirming test on three different samples: •

a reference solution (known to contain the ion of interest)



tap water (which may or may not contain the ion)



a control (distilled water, known not to contain the ion).

4. For some of the visible changes, what methods or materials can be used to aid in the determination of the results? 5. You will test for the presence of the cations iron (III), Fe 3+ , and calcium, Ca 2+, as well as the anions chloride, Cl -1, and sulfate, SO4 2-. Given the following chemicals, determine to which ion they provide the confirming test. AgNO3 (silver nitrate), HC2H3O2 with Na2C2O4 (acetic acid and sodium oxalate), KSCN (potassium thiocyanate) and BaCl2 (barium chloride). 6. What is the balanced chemical equation for the reaction. 7. Give all N.I.E.s for the reactions. 8. Explain the statement: “The alkalinity of a water sample cannot be simply measured by a pH meter” 9. Discuss the sources of alkalinity in water found in Guelph. 10. Identify the major species accounted for the alkalinity in natural water samples.

PURPOSE: In this activity you will use some chemical tests to check for the presence of certain ions in aqueous solution. You will investigate two cations and two anions.

Last Revised 1/11/10

PROCEDURE: Complete the confirming tests (checked by the teacher) by applying 3 drops of test solutions on 2.0 mL of the respective reference solution provided by your teacher, on 2.0 mL tap water, and on 2.0 mL of distilled water. Test for the acidity of distilled water using the following procedure: 1. Pipet 10.00 mL of distilled water into an flask and add 4 drops of phenolphthalein 2. Make up a 100.0 mL solution of 0.010 M NaOH using a volumetric flask and the correct mass of NaOH. 3. Fill a buret with 0.010 M NaOH 4. Add NaOH to the distilled water until a light pink colour is seen. 5. Repeat the titration 3 or more times until you have 3 trials that are within 1% Test for the alkalinity of hard water using the following procedure: 1. Prepare 250.0 mL of 0.020 HCl solution. 2. Obtain 200 mL of tap water in a beaker and pipet 50.00 mL of the tap water into a flask. 3. Fill a buret with 0.020 M HCl 4. Add 6 drops of methyl orange indicator to the sample and titrate with HCl solution until the solution turns tangerine orange-pink. 5. Repeat the titration 3 or more times until you have 3 trials that are within 1% ANALYSIS AND DISCUSSION: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Why was a control used in each test? Why was distilled water chosen as the control? Describe some difficulties associated with the use of qualitative tests. How would you choose to test for iron, calcium, chlorine and sulfate ions if you could use ANY solutions to test for ions? Use a selective ion flowchart to describe your procedure. These tests cannot absolutely confirm the absence of an ion. Why? How might your observations have changed if you hadn’t cleaned your test tubes thoroughly between each test? Explain why distilled water may be acidic. Calculate the alkalinity of the tap water sample in terms of moles of H+ ion per litre. Why is methyl orange used as an indicator in the determination of water alkalinity? What are the possible reactions for acids and bases in tap water?

Last Revised 1/11/10

ACID INDIGESTION AND ANTACID EFFECTIVENESS INTRODUCTION: 1. What is the normal percent concentration of hydrochloric acid in the stomach? 2. What factors can lead to higher levels? 3. What is this condition commonly called? 4. Recommended dosages of the anti-acid will be allowed to react with an acid solution. The solution will then be titrated with sufficient base to neutralize the remaining acid. How will this amount of required base relate to the effectiveness of the anti-acid treatment? PURPOSE: The purpose of this investigation is to compare various brands of antacid medications as to their relative effectiveness. PROCEDURE: 1. Standard the sodium hydroxide solution. 2. Obtain three different antacid treatments. Use uncoloured products that won’t mask the indicator color change. 3. Transfer 50.0 mL of “stomach acid” (0.10 M HCI) to each of three flasks. 4. Find the mass of and add the recommended dosage of one of the three antacid treatments to each of the three flasks and stir. If the antacid is a tablet, grind it in a mortar and pestle to hasten dissolving. Allow the treatments to work for ten minutes before continuing. 5. Add three drops of the phenol red indicator to each of the three flasks. 6. Titrate with the standardized NaOH until the first permanent change to red occurs. ANALYSIS AND DISCUSSION: 1. Give the balanced equation for the neutralization of “stomach acid” using sodium hydroxide. 2. Determine the amount of antacid and compare with manufacturer’s claims. Calculate the percentage difference and discuss any differences. 3. Which antacid is most cost effective? Show your calculations in order to justify your answer.

Last Revised 1/11/10

REACTION OF METAL NITRATES WITH SODIUM HYDROXIDE INTRODUCTION: 1. What is the balanced chemical equation for the reaction of silver nitrate, zinc nitrate, and aluminium nitrate with sodium hydroxide solution? 2. Why is it important that these solutions contain nitrate ions and no other anions? 3. If you are given an unknown concentration of the nitrate solutions, describe TWO methods that could be used to find the concentration of these solutions – one method must include the use of sodium hydroxide solution? 4. Explain the concept of solubility and how solubility can be used by analytical chemists to detect what ions are present in a solution. PURPOSE: The purpose of this experiment is to use stoichiometry to determine the concentration of zinc nitrate and aluminium nitrate solutions. SAFETY: • Sodium hydroxide is corrosive and must be handled with care. PROCEDURE: • Write up a detailed procedure for the method that you will use and have it checked by your teacher. • The solutions will be given to you by the teacher and will have a known concentration – part of your lab evaluation will be to determine the concentration using stoichiometry. ANALYSIS: Calculate the concentration of the nitrate solutions used in the reactions and determine the accuracy of the stoichiometric methods. DISCUSSION: Account for any differences between the results from both methods. Which method yielded the most accurate results? Explain fully. EVALUATION: Explain how this experiment could be improved and account for all errors.

Last Revised 1/11/10

ANALYSIS OF VITAMIN C INTRODUCTION: 1. Vitamin C tablets contain what acid as the active ingredient? 2. What is the reaction equation for that acid with sodium hydroxide? 3. What other ingredients in the tablet could cause the determination of the active ingredient to become difficult? 4. Are Vitamin C tablets water-soluble? 5. Sodium hydroxide solution requires standardization prior to using in a titration. Determine the standardization procedure. PURPOSE: In this experiment you will analyze a tablet of Vitamin C and calculate the percentage of ascorbic acid present, H2C6H6O6, in the tablets. PROCEDURE: 1. Standard the sodium hydroxide solution. 2. Mass out a tablet of Vitamin C and record. 3. Place the tablet in an Erlenmeyer flask, add about 50 mL of warm distilled water, and crush the tablet with a glass stirring rod. 4. Add two or three drops of phenolphthalein indicator to the flask and titrate with sodium hydroxide solution until the endpoint is reached. 5. Repeat 3 times. ANALYSIS/DISCUSSION: 1. Determine the percentage of ascorbic acid (vitamin C) present in the tablet. 2. Determine the percentage difference with the manufacture’s claim. 3. Account for any difference.

Last Revised 1/11/10

ANALYZING A MIXTURE USING STOICHIOMETRY INTRODUCTION: You are given an unknown sample of contaminated sand. The sand has been contaminated with Copper (II) Nitrate and Sodium Chloride2 and Iron3 . Explain what sand is usually made from and how sand is formed. HYPOTHESIS: Outline all reactions that will be used to displace the copper (II) nitrate and sodium chloride from the sand. EXPERIMENTAL DESIGN: Determine a method to find the percent by mass of copper (II) nitrate and sodium chloride in the sand sample. PROCEDURE: Design a list of materials and a procedure to find the mass of copper (II) nitrate and sodium chloride in a given mass of sand using stoichiometry. ANALYSIS: 1. 2. 3. 4. 5.

What mass of Copper (II) Nitrate was in the sand sample? Show all calculations. What mass of Sodium Chloride was in the sand sample? Show all calculations. What mass of Iron was in the sand sample? Show all calculations. What was the mass of sand in the sand sample? Show all calculations. Calculated percentage by mass for all impurities in the sand.

DISCUSSION: 1. What chemicals did you use to extract Copper (II) ions from the sand? Explain why these chemicals were used? 2. How did you extract the Iron from the sample? What properties of Iron allowed its extraction from the sample easily? Explain. 3. How would your procedure have been different if Iron (III) Chloride had been present in the sand instead of elemental Iron? 4. What assumptions did you make to complete this experiment? 5. What possible sources of error did your procedure introduce? 6. Would your procedure have worked if you had a contaminated sugar sample instead of a contaminated sand sample? Explain. How could you have changed your procedure?

2 3

Chemistry 11, McGraw-Hill Ryerson, Analyzing a Mixture using Stoichiometry, pp. 274-275 Iron in Cereal - Separation

Last Revised 1/11/10

Moisture Content of Popcorn - Statistical Analysis Introduction: 1. What is standard deviation? Why is it important in determining the quality of experimental data? 2. Why are multiple trials important? Explain what is meant by the term “outlier”. Purpose: The purpose of this experiment is to determine the moisture content of popcorn and to use basic statistics to analyze the results. Equipment/Materials: Popcorn clamp + retort stand

24-hole well plate Bunsen burner

balance (1 or 0.1 mg sensitivity)

Procedure: 1. Select 20 kernels of popcorn. Place each kernel in a well of a well plate. Additional kernels are used in case samples are burned or scorched. (Keep track of the brands that are used) 2. Determine the mass of each kernel, and record the mass in your data table. 3. Heat the flask gently and keep the popcorn kernel in constant motion. As soon as the kernel pops, invert the flask and let the popped kernel fall onto the lab table. If it sticks, a stirring rod may be used to dislodge it. 4. Return each popped kernel to its position in the well plate. Continue until you have 15 popped kernels that are not burned or scorched. 5. Determine the mass of each kernel after popping. Record this mass in your data table. Calculations: 1. Determine the mass lost by each kernel of popcorn and the percent of mass lost. For the 15 kernels that you have selected, calculate the average or mean percent mass lost. 2. Subtract the mean percent mass lost from each individual percent mass lost. Record this value in the data table. 3. Finally, square this final value and record the value in the data table. 4. Using the formula Standard Deviation =

∑ (x − x ) (n − 1)

2

,

calculate the standard deviation for the percent mass lost. 5. In a “normal” distribution, 67 % or 2/3 of the samples are within +/- one standard deviation of the mean. Determine the number of trials that fall within this range for your data. € Questions: 1. What was the nature of the mass lost? What indications did you have for this? Water loss from the inside of the kernel. If the flask is not too hot, moisturre may be seen leaving the flask. 2. How many of your samples showed a mass loss that was +/- one standard deviation from the average mass lost? 3. Using the average mass of a popcorn kernel, how many kernels would you expect to find in a onepound bag of popcorn? 4. If more than one brand of popcorn were tested, was there a difference in the moisture content? How might this affect popping? Older popcorn that has lost moisture often does not pop as well. Last Revised 1/11/10

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