and Titrations Lesson Created by: Lauryn Atwood Length of lesson: 1 week Description of the class: Heterogeneous Name of course: Chemistry Grade level: 10-12 Honors or regular: Regular Source of the lesson: http://www.ausetute.com.au/titrcurv.html http://www.cstephenmurray.com/acrobatfiles/ipc/chapter22to25/chap25no1.pdf http://www.sciencecompany.com/images/phscale.gif http://teachers.ausd.net/classlink/getfile.ausd?fileid=45821 TEKS addressed: (2) Scientific processes. The student uses scientific methods to solve investigative questions. The student is expected to: (E) Plan and implement investigative procedures, including asking questions, formulating testable hypotheses, and selecting equipment and technology, including graphing calculators, computers and probes, sufficient scientific glassware such as beakers, Erlenmeyer flasks, pipettes, safety goggles, and burettes, and an adequate supply of consumable chemicals; (F) Collect data and make measurements with accuracy and precision; (G) Express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures. (I) communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology-based reports. (10) Science concepts. The student understands and can apply the factors that influence the behavior of solutions. The student is expected to: (I) define and use the hydrogen or hydroxide ion concentrations to calculate the of a solution I. Overview The purpose of this lesson is to familiarize students with the concept of. Students will conduct neutralization reactions and understand how the changes. Students will construct titration curves and determine endpoints of titration from these curves, then use this endpoint to help in the calculations of molarity of an unknown base. The students will also conduct an investigation of of household products. II. Performance or learner outcomes Students will be able to: Write balanced neutralization reaction equations Find the endpoint of titration Construct a titration curve Titrate an unknown concentration of base with an acid Calculate the molarity of an unknown base Investigate the of household products III. Resources, materials and supplies needed Engage: 5 test tubes per group 1 beaker per group 5 test tubes for the teacher 1 beaker for the teacher 1 pipette per group Universal Indicator Litmus paper (5 pieces per group) Phenolphthalein
Chemicals: 0.1 M HCl, 0.1 M NaOH, 0.1M CH 3 COOH, 0.1 M NH 3, water Goggles per student Explore: 1 burette per group 1 graduated cylinder per group 2 beakers per group Goggles per student 1 funnel per group meter per group Chemicals: 0.1 M HCl, ~0.1 M NaOH Computer per group (with Excel) Elaborate: Universal Indicator Buffers ( 1-14) 8 test tubes per group meter per group Milk Lemon juice Aspirin Shampoo Bleach Windex Coca-cola Dishwashing soap IV. Supplementary materials, handouts. (Also address any safety issues Concerning equipment used) exit slip, titrations quiz, indicators quiz, Titrations lab, of household products lab, Acids/Bases PowerPoint, MSDS Sheets V. Safety Issues Chemicals are used in this lesson. Students should wear goggles, long pants (past the knee), and close-toed shoes at any time they have chemicals. Students may opt to wear aprons as well to protect their clothes. MSDS Sheets for each of the four chemicals (HCl, NaOH, CH 3 COOH, and NH 3 ) are provided at the end of the lesson. If any glass breaks, students should notify the teacher immediately and keep people clear from the area. The teacher should then dispose of the broken glass properly (not in a trash can). VI. Accommodations for learners with special needs (ELLs, Special Ed, 504, G&T) ELL, Special Ed, 504: Guided notes G&T: lesson extentions (polyprotic acids)
Five-E Organization Teacher Does Probing Questions Student Does Critical questions that will establish prior knowledge and create a need to know Engage: Learning Experience(s) [Indicator Activity] Advanced preparation: Fill five labeled (A-E) test tubes ¼ full with chemicals of different levels before class. (1-HCl, 2-CH 3 COOH, 3-H 2 O, 4-NH 3, 5-NaOH) Also, prepare the Universal Indicator, by putting ~5 drops in each table s beaker, then fill the beaker with water. Expected Student Responses/Misconceptions Each group has 5 test tubes with different liquids in each. Put 3 drops of the liquid from your beaker into test tube A. Add 3 drops of the liquid from the beaker into test tube A to each of the other 4 test tubes. In your beaker, there is water with something we call a indicator. It tells us about an important property of compounds, called. What observations can you make about these 5 liquids? What observations can you make about your beaker? What do you think will happen when you add 3 drops of the liquid from the beaker into test tube A? What happened? Why? What will happen when you add 3 drops of the liquid from the beaker into test tubes B-E? What happened? Why? They are clear; they might be different. It is also clear. It might change colors; nothing. The solution turned red! A chemical reaction They will also turn red; they may turn different colors. They turned different colors! There were different chemicals in each of the beakers that reacted differently with the liquid from the beaker
The of a compound is a measure of acids and bases and goes by a scale from 0-14. The more acidic a compound is, the lower the. The more basic a compound is, the higher the. Neutral compounds, like water, have a of 7. Show the Universal Indicator scale. This scale shows the different colors that the solution will turn when it hits a certain. We can essentially figure out the concentration of H + ions in a solution by knowing its. Use phenolphthalein as a demonstration and then have students use litmus paper to demonstrate uses of other indicators. Approx. Time 20 mins Evaluation(Decision Point Assessment): Indicators quiz. exit slip. What is a Universal Indicator? How is it different from a specific color indicator? What is? The assessment you will use to determine what to do next. Shows at a variety of levels A specific color indicator only changes color once, while a universal indicator can change to a bunch of different colors, depending on the. A measure of acids and bases. It measures the hydrogen ion concentration. What student outcome will indicate that you should move on to the exploration? What will you do if the outcome is something else? Explore: Learning Experience(s) Today, we ll be talking about neutralization reactions. We discussed neutralization Critical questions that will allow you to decide whether students understand or are able to carry out the assigned task (formative) Expected Student Responses/Misconceptions
reactions last week and a group gave a presentation on them. You are going to conduct two neutralization reactions, or titrations, using a strong acid and a strong base. One titration will be done with a color indicator. The other will be done with a probe. Write down a hypothesis in the correct space on your lab sheets. Separate students into groups of four. Pass out job cards. You will have a specific job for this experiment. Titrator: Adds a few drops of the titrant (base). Burette reader: Reads the burette after every few drops of titrant are added. Probe Reader: Reads the meter to get a value for each burette reading. Recorder: Records the and What is a neutralization reaction? Where would a strong acid be on the scale? A strong base? If we are mixing these two substances, which are on opposite ends of the spectrum, together, what might we want to know? What do you think will happen to the when you mix these substances together? Why? What are we forming in a neutralization reaction? What is the of water? What does this mean for the of the substances you mix together? When an acid and a base combine to form a salt and water. 0; 14 What the ending will be. Misconceptions: Nothing; they will change colors; they will become more acidic/basic. Various responses. A salt and water. 7 (neutral) They should be about 7.
burette reading on a blank sheet of paper after each few drops. [Teacher Note: If students don t have access to a probe, a universal indicator can be used, marking the volumes of base used for each color change.] If you are the recorder, rinse the burette. probe readers, set up the probe in the beaker. Burette readers, fill the burette after it is rinsed and tell the recorder the initial reading on the burette. Titrators, prepare the analyte. Pass out lab skills checklist. Conduct titrations and assess lab skills. After you finish conducting the titration, clean up properly. [Constructing a Titration Curve] Construct a titration curve by following the instructions given. Find and record the endpoint of titration for your experiment. What do you notice about this curve? What do you think is happening when the is steady at the beginning? What is happening during the steep, quick rise? What is happening when the becomes steady again towards the end of your titration? How can we determine the endpoint of titration? It gets really straight and perpendicular in the middle and levels off horizontally on both ends. Moles acid >> moles base Moles acid ~ moles base Moles base >> moles acid Find the middle of the steep part of the curve.
Approx. Time 70 mins Evaluation(Decision Point Assessment): Titration Lab Skills Checklist during the lab. Alternative Assessment: Skill Tasks Titration lab Titrations quiz The assessment you will use to determine what to do next. What student outcome will indicate that you should move on to the explanation? What will you do if the outcome is something else? Students should all average proficient lab skills. If not, go over important lab skills needed for this lab. Students will use cooperative roles to conduct titrations. Explain: Learning Experience(s) [Acids/Bases PowerPoint] [Stoichiometry Review] Review stoichiometry and dimentional analysis. [Calculating the Molarity of an Unknown Base] If we know the concentration of the acid, we will be able to calculate the concentration of the base! Write the balanced chemical equation on the board. The coefficient for each compound (the number in front) represents the number of moles of that compound. Critical questions that will allow you to help students clarify their understanding and introduce information related to concepts to be learned Why is stoichiometry useful? How can stoichiometry be used in this experiment? What is the balanced chemical equation for the titration we did? There are no numbers in front of any of these compounds, what does this mean? So does this mean there was constantly 1 mole of HCl when we titrated? Expected Student Responses/Misconceptions It allows us to do conversions To find the concentration of the base. HCl + NaOH NaCl + H 2 O That it represents only one mole for each compound. No.
These numbers are ratios. This means that at equilibrium for every one mole of HCl, we have one mole of NaOH, one mole of NaCl, and one mole of water. This gives us (0.025X) moles. Now we know the number of moles of base, but we re trying to find the concentration of the base. What is the known concentration of acid? (Given) If we have X M of acid, what does the M stand for? How can we figure out how many moles of acid we started out with? What do we know about the ratio of moles in this titration? What does this mean about moles at the endpoint of titration? How many moles of base got us to the endpoint of titration? What are the units for concentration, again? What else do we know about the base in this experiment? At which point in our titration curve are we looking? Why? [value - X] Molarity; moles per liter Multiply by the amount (in liters) of acid used. There is a 1:1 ratio. There will be an equal number of moles of acid and base. (0.025X) moles Molarity; moles per liter How much we added. The endpoint Because that is when the is 7 and the moles acid = moles base for this experiment. Looking at your titration curves, find the endpoint of titration. Looking at this stoichiometry, let s take our balanced equation and look at both sides to find the concentration a different way. [Use the empirical formula, M 1 V 1 = How much base did you add to get to the endpoint of titration? How can we use this information to find the concentration of the base? Y ml Convert ml to L, then divide the number of moles by this number.
M 2 V 2 to find the concentration again] Approx. Time 45 mins Evaluation(Decision Point Assessment) Titrations quiz The assessment you will use to determine what to do next. What student outcome will indicate that you should move on to the extension? What will you do if the outcome is something else? Extend / Elaborate: Learning Experience(s) [ Testing of Household Products] We are going to investigate of household products. First, hypothesize whether each of the items we are testing are acids or bases. Justify your hypotheses. Conduct investigation. (from http://teachers.ausd.net/classli nk/getfile.ausd?fileid=45821) Approx. Time 45 mins Evaluation(Decision Point Assessment): Alternative assessment - Investigation Critical questions that will allow you to decide whether students can extend conceptual connections in new situations The assessment you will use to determine what to do next. Expected Student Responses/Misconceptions What student outcome will indicate that you should move on to the final evaluation? What will you do if the outcome is something else? Evaluate: Lesson Objective(s) Learned (WRAP UP at end) -> Summarize Submit a 1 page paper taking the stance of either a company that manufactures meters, a company that produces a specific indicator (like phenolphthalein), or a company that produces a universal indicator. Give an Critical questions that will allow you to decide whether students understood main lesson objectives Expected Student Responses/Misconceptions
explanation as to why the consumer would be better off using your product for their experiments than another. Prepare a poster to sell your product to the class. Project question: How do and titrations relate to my topic of interest? Approx. Time 40 mins
Acids/Bases PowerPoint Presentation Page 1
Acids/Bases PowerPoint Presentation Page 2
Titrations Materials: 2 beakers 1 burette 1 funnel 1M HCl Unknown concentration of NaOH Stir/hot plate Magnetic stir bar Your task: To determine the unknown concentration of NaOH Job Roles: (CIRCLE YOUR JOB ROLE) Titrator: Adds a few drops of the titrant (base). Burette reader: Reads the burette after every few drops of titrant are added. Probe Reader: Reads the meter to get a value for each burette reading. Recorder: Records the and burette reading on a blank sheet of paper after each few drops. Preparation Procedure: Rinse a burette with your base Recorder Put a waste beaker underneath the burette. Using your funnel, put a small amount of base in the burette and let it run through, with the stopcock open. Preparing the titrant Burette Reader The titrant is the substance you will use to titrate (in this case, it is the base). Carefully fill the burette to the 5mL mark (at the top of the burette) with sodium hydroxide (NaOH), using your funnel. Record this as your initial reading. Preparing the analyte Titrator The analyte is the substance you will be titrating (in this case, it is the acid). Collect 25mL of 0.1M hydrochloric acid (HCl) in a graduated cylinder. Record the exact amount of HCl you have collected. Transfer the HCl into a clean, dry beaker. Preparing the setup Probe Reader Put the beaker with the analyte underneath the burette that is filled with the titrant. Secure the probe on the side of the beaker. Be sure that the glass bulb is submerged in the liquid, but does not touch the bottom of the beaker. Put a magnetic stir bar in the beaker and turn the stirrer on (not the heat!). Titration Procedure: Titrate the analyte with the titrant with a few drops, then stop record the burette reading and. Your solution s will not change much in the beginning. It is okay to titrate 2-3mL when it doesn t change much. When the numbers do start changing rapidly, only titrate 1-3 drops at a time. Do this until the of your solution becomes steady again.
Data: Volume of HCl Initial Burette Reading: (continued) ml of NaOH added ml of NaOH added 0 Initial :
Constructing a Titration Curve: Open Microsoft Excel. In the first column, enter the amount of base you added (This is equal to the Burette Reading Initial Reading). In the second column, enter each corresponding reading. Create a scatter plot of the amount of base added vs. the. Include a title and axes labels. Don t add a smooth curve. Print out a copy for each group member. Clean up: Put any leftover acid in the acid waste container. Put any leftover base in the base waste container. Put the titrated chemicals in the neutral waste container. Wash all glassware. Titration Lab Skills Checklist: 1. Correctly read a meniscus. Level: Needs Improvement Proficient Exemplary 2. Know the lab materials and safety equipment for this lab. Level: Needs Improvement Proficient Exemplary 3. Know the procedure of the lab. Level: Needs Improvement Proficient Exemplary 4. Use and interpret indicators ( paper and cabbage juice). Level: Needs Improvement Proficient Exemplary 5. Collect, organize, and graph data. Level: Needs Improvement Proficient Exemplary 6. Formulate conclusions of the experiment. Level: Needs Improvement Proficient Exemplary
of Household Products Lab Source: http://teachers.ausd.net/classlink/getfile.ausd?fileid=45821 Introduction: Many kinds of solutions must be tested to determine whether they are acidic, basic, or neutral. The scale represents the hydronium ion concentration of a solution and is used to indicate how acidic or basic a solution is. The normal range is from acidic 1 to neutral 7 to basic 14. The most accurate method of determination is by use of an electronic instrument known as a meter. For simpler, though less accurate determinations, indicators are commonly used. Indicators are organic compounds that change color with changing. Some indicators are mixtures of compounds, each of which changes color at a different. In part I, you will observe the variation in color with of a natural indicator. In part II, you will use the same natural indicator to determine the of various household products. Materials: Cabbage juice, Buffers ( 1-14), 8 test tubes, meter, household products Safety: Wear safety goggles and aprons. Objective: 1. Observe the color of cabbage juice in solutions with ranging from 1-14 2. Determine the approximate of household products using cabbage juice 3. Determine the of household products using a meter 4. Determine whether the household products are acidic, basic, or neutral Procedure: Part I: 1. Observe the colors of the cabbage juice in the test tubes labeled 1-14 and record the colors in table 1. This will be used as a reference. Part II: 2. Add approximately 2 ml of the household products into 8 labeled test tubes. 3. Add approximately 2 ml of cabbage juice into the above test tubes. 4. Observe and record the colors of the solutions in table 2. 5. Compare the colors of the products with the cabbage juice to the colors from table 2 and determine the approximate of your products. 6. Test the of each of the household products using a meter. Record in table 2. Part I Color of Cabbage juice 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Part II Product Name Milk Lemon Juice Aspirin Shampoo Bleach Windex Coca-Cola Dishwashin g Soap Color of Product & Cabbage Juice Approximate using meter Page 1 Post-Lab Questions 1. What are the advantages and limitations of using an acid-base indicator such as cabbage juice to test the of household products?
2. How do the values obtained from the cabbage juice compared with the one obtained from the meter? Explain any discrepancy. 3. Draw a scale (1-14) and place the products at the appropriate. 4. Which products are acidic? Basic? Neutral? Explain your reasoning. 5. Which product contains the highest concentration of hydrogen ions? Lowest? Explain your reasoning. 6. Many commercial products are advertised as balanced. Explain what is meant by the term balanced? 7. Normal rain has an approximate of 5 whereas acid rain has an approximate of 3. Acid rain is how many times more acidic than normal rain? Explain. Page 2
Conclusion: Summarize the results of the experiment. List possible sources of errors and suggest ways to improve the accuracy/precision of the results. Page 3
Name: Exit Slip 1. To mix acids and bases to cancel each other out and make salt water. 2. A compound that adds H+ ions to water. 3. Equal number of H+ and OH- ions; water is an example. 4. A compound that adds OH- ions to water. 5. When caused by pollution ( < 5.6). A. Acid B. Base C. Neutral D. Neutralize E. Acid Rain Name: Titrations Quiz Balance this neutralization reaction: H 2 SO 4 + KOH K 2 SO 4 + H 2 O What is the difference between the endpoint and the equivalence point of a titration? Solution A ( 4); Solution B ( 2) Which has more H+ ions? Which has less OH- ions? Name: Indicators Quiz What is the purpose of an indicator? What is a Universal Indicator? How is using an indicator different than using a probe?