Msyow.weebly.com



NH4Cl - Teacher NotesIn the Shakashiri demo, a glass tube 1-m in length and with an outside diameter of 22 mm is used. ?In building this activity, many different clear tubes were tested, including: glass buret tubeacrylic tubes of varying length and diameter from TAP Plastic storesclear plastic strawspolystyrene pipettes with ends sawed off (BD bioscience serological individually packed)Cotton balls are used in the demo materials, while pyrex/glass wool, cotton balls, and cotton swabs were tested. cork with q-tip seems simplest/easiest way to handle chemicals. Various injecting mechanisms were tried:what is used in the demo, which is rubber stoppers with cotton balls soaked with solution. corks with cottonglass wool with rubber stoppers and syringes to inject a set volume of each substance (amount of glass wool varied, not controlled for)corks with q-tip sticking out of each endcorks with q-tip pretty flush with cork endVarying concentrations were tested to try to keep the toxicity of chemicals to a minimumLab calls for 12M HCl and 6M NH36M HCl with both 6M NH3 and 3M NH3 in varying tubes - HCl did not travel down the tube and the NH4Cl ring formed at the HCl end. Seems that lower concentrations of HCl does not have a vapor pressure (VP) therefore it will not form gas to diffuse down tube. Tube lined with pH paper to visualize the gas travelling/diffusing down the tubeFound that the presence of pH paper significantly hindered the HCl from traveling down the tube, and at some point, stops it completely. ?Unsure as to what the interaction is. Hypothesize that the paper is actually absorbing the HCl vapor. HCl has a very defined front as it travels down tube, while NH3 has a very diffused front with some particles travelling faster down the tube and pH paper changing colors slightly to indicate as such, while the end of tube pH paper changes color to darker blue slowly. Cork with cotton swab Rubber stopper with cotton swabAcrylic tube, cotton ball, cork, pH paper lining insidePipette, cotton swab, cork, pH linedPipette with holes, cotton swab, cork, pH taped to outside to cover holesAcrylic tube, cotton swab, cork at different time intervals – ring migrationPROCEDURE/DATA/ANALYSISEngageTeacherStudent1. ?Show demo of the reaction between ammonia and hydrochloric acid. ?This can be done by soaking the tips of two q-tips with each chemical and holding them near each other. The teacher will talk briefly about the chemical reaction that is happening and about diffusion. (5-7 min)1. ?Students will observe the demonstration and should see a white precipitate form in the air as the two chemicals come into contact and react with each other. ?Students will complete the first question on their handout. T: Ammonia (NH3) is a gas and hydrochloric acid (HCl) is also a gas. ?They are both in solution, but are both very volatile, which means they readily become gases. ?So even though the Q-tip is soaked with a liquid or aqueous solution (chemical dissolved in water), gas is forming from each of the solution soaked Q-tips. ?When the two chemicals come in contact, they chemically react and form a white solid precipitate called ammonium chloride.Talk a bit about diffusion in terms of things the students are familiar with, like various smells - perfume, flatulence, etc. ?You may even spray some perfume at the front of the class and have someone be the timer and have students raise their hand when they smell the perfume and collect some of that data. ?Do all gases travel at the same speed? What do they know about this? Do they know the relationship between kinetic energy and temperature at this point? (Do they need to? or is this something that I want to focus on in this lesson?) What determines how fast you will smell something? How do you know the gas is moving if you cannot see it? Will the people in the back of the room ever smell the perfume before the people in the front of the room? Student Handout 1Q1. ?On the above image of a tube, draw where you think the two gases will meet and form the ammonium chloride ring. Explain why you drew what you drew, where you drew it. ?**diffusion: the tendency of molecules in a gas to move from areas of high concentration to areas of low concentration. ?How does the gas start at the cotton ball and end up somewhere in the middle of the tube? Why does it do this? 2. ?Acid/base connection: Take a strip of pH paper and dip one in each of the two solutions. ?Show the students and have them answer the next question. Try holding a strip of pH paper above the solution or away from the Q-tip and see if the color changes at all. ?You can talk a bit about what is happening or have students hypothesize as to what is happening to the paper, why it is changing colors. Q2. ?Write down your observations from the pH paper demonstration and answer the following questions using the information provided. ?????chemical ???????????????????observations ???????????????????A/B ????NH3, ammonia ______________________HCl, hydrochloric acid_________________Low pH (<7) indicates an acid whereas high pH (>7) indicates a base. ?Use the pH paper key to identify each chemical as either an acid (A) or a base (B) above. Salts are ionic compounds that form from a cation (+) and an anion (-) and are neutral (pH=7). ?What color will the pH paper be in the presence of a neutral compound? ___________________________3. ?Talk explicitly about the chemical reaction taking place: NH3 (g) + HCl (g) → NH4Cl (s) ← a salt. NH4+ and Cl-On the board, identify what color each will turn the pH paper to provide students with a visual/referenceQ3. ?With this new information, in the tube above, draw a strip of pH paper that will run through the tube. ?Color in or label what color you think different parts of the paper will be. ?Briefly explain what you have drawn and why. Explore/ExplainTeacherStudent4. ?Brief instructions for the activity. ?Each group should have 4-5 students. First thing they should do is assign roles. ?(Maybe this happens before engage...and they are answering their questions in the presence of their group members). ?In doc, insert check boxes at each action step. P1. ?In your groups, assign each member a role. ?What is your role? _______________Once you are assigned a role, review the procedure and make sure you are clear of your role and when it is pertinent. Make notes in the text and margin to emphasize important steps and things to remember. ?You may choose to use a highlighter. P2. Label one end of the clear tube “HCl” and the other “NH3”. Come to a group consensus about where you think the ammonium chloride ring will form in the tube, and use the overhead marker to make a mark on the tube. P3. Cut a strip of pH paper ~1 inch shorter than the length of the tube and slide/center it into the tube.P4. Clamp the tube horizontally between the two stands, as shown in the image. Make sure the pH strip is centered. ?You may use a small piece of tape if necessary, to hold it down. ?P5. Place a small cotton ball in the hollow of each stopper. ?Dip one of the stoppers holding a cotton ball into a 50-mL beaker containing the HCl and the other into a 50-mL beaker containing the NH3. ?P6. ?Simultaneously insert the two stoppers into the appropriate ends of the tube and start the timer. Make observations and record them on your worksheet (Q4).P7. ?When you see the ammonium chloride ring form, draw a line with the overhead marker to mark on the tube where it formed and make note of the time. Make some measurements and answer Q5. Check in with students/groups during their procedure, especially near the end and illicit ideas about what is happening and what they are observing. ?Hopefully, students will be marvelling at how cool it is to see the pH paper change colors and visualize the movement of the gases. Q4. ?Draw what you observed in the experiment. Use colors and words to explain. ?Does traveling further mean that it was traveling faster? What other factors might you take into account that you think might affect how far the gas travels? Q5. ?Draw a line on the tube where the white ring formed. Measure how far the ring is from each end/chemical. NH3:_____HCl:_____Which gas traveled further? _____How much further did it travel? _____ ?Q6. ?Compare these results to your predictions. ?Discuss with your group how they compare. ?Was your prediction correct? Do you think your reasoning is accurate? Was your prediction very different from what actually occurred? Why might that be? Come up with some explanations and/or questions. ?Write down a few things from your discussion. Option 1: Bring the class back together at this point to discuss findings and guide toward understanding. Option 2: Groups work at their own pace and check in with you at this point and get their next handout. Students may choose to work together in a group to answer the questions or within their groups in smaller pairs or triplets. Student Handout 2 (Not to be passed out before completing Student Handout 1)Q7. ?You know that gas molecules are in constant, random motion in a straight line. ?A gas molecule will continue moving in a straight line until it hits something, at which point it will change directions. ?We will analogize a pool ball to a gas molecule. You can imagine a pool ball continuing in a straight line until it hits something, then it moves in another direction until it hits something else, just like a gas molecule, except gas molecule constantly moving. Imagine two (identical) pool balls that are pushed with the same force along the same straight line from opposite ends, where do you think they would collide? Why? Experimental dataExpected: 1.46, 1.28TrialTubeEnds[HCl][NH3]pH paper?NH3/HCl = distance ratioTime1glasssyringe12M6MYes48.5/13.33.6532.5 min2glasssyringe12M6MNo36/261.387.5 min3glasssyringe6M3MNoN/A @HCl end8 min4glasscork/q-tip12M6MNo27.5/26.51.047 min4b“““““5plasticcork/1-tip6M3MNoN/A@HCl end6 min6plasticcork/cotton12M6MNo18.2/10.81.691.5 min7plasticcork/q-tip12M6MYes20.2/8.52.384 min8plasticcork/q-tip12M6MNo15.8/111.441m23s8b“““““15.3/11.51.331m30s8c““10M6M“19.5/72.793 min8d““12M3M“14.3/12.51.14x1m30s8e““10M3M“9plastic w/ holescork/q-tip12M6MYes, taped along outside along holes17.0/9.51.792m30s10plasticcork/q-tip12M6MYes, soaked w DI H2O along inside22.9/3.76.195m42s11plasticcork/q-tip12M6MYes, filter paper soaked w universal indicator20.4/63.4~4 min12strawq-tip12M6MN17/7.22.36<40s12b“““““11.2/8.31.35<30s12cstrawq-tip10M6MN15.5/43.88<1 min12dstrawq-tip10M3MN13straw w holesq-tip12M6MYes, taped along outsideAcylic tube (TAP) 1 cm in diameter inside, cork/q-tip, 12M/6M, no pH, 33 cm longring formed at 1m30s, 12.5 cm from HCl end and 20.5 from NH3 end (20.5/12.5 = 1.64x)Then it migrated farther and farther toward HCl. time elapsetime incrementNH3(33-HCl)HClRatio(NH3/HCl)Rate of ring move(0.5/inc) cm/s1m30s020.512.51.6402m30s60s21121.750.00833m8s38s21.511.51.870.0134m42s221120.0125m60s22.510.52.140.00836m60s23102.30.00837m10s70s23.59.52.470.00718m20s70s2492.670.007110m100s24.58.52.880.00512m120s2583.130.004214m120s25.57.53.40.004217m150s267.03.70.0033Timed trial using glass buret tube, glass wool, rubber stopper, 1cc syringe with luer lock, 12M HCl, 6M NH3, one tube with pH paper lining length of the tube, one tube without pH paper. Length of tube = 62 cm. Injected 0.5 mL of each chemical at each end. TimeHCl moved ___ cm toward centercm/mintotal distance/total time cm/min(section distance/2.5 min)NH3 moved ___ cm toward centerno pH control ~7.5 min26 cm3.474.836 cm36 cm NH3 /26 ?cm HCl= 1.38x fartherNH3 than HClw/o pH paper2.5 min (150s)7 cm2.86.817 cm5 min8.5 cm (1.5 cm)1.7 (0.6)4.4 (2)22 cm (5 cm)7.5 min 9.5 cm (1.0)1.27 (0.4)3.53 (1.8)26.5 cm (4.5)10 min 10 cm (0.5)1 (0.2)3 (1.4)30 (3.5)12.5 min10.5 (0.5)0.84 (0.2)2.64 (1.2)33 (3)15 min11 (0.5)0.73 (0.2)2.4 (1.2)36 (3)17.5 min11.5 (0.5)0.66 (0.2)2.11 (0.4)37 (1)20 min11.5 (0)0.58 (0)2.0 (1.2)40 (3)22.5 min12.5 (1.0)0.56 (0.4)1.8 (0.4)41 (1)25 min12.75 (0.25)0.51 (0.1)1.76 (1.2)44 (3)27.5 min13.3 (0.55)0.48 (0.22)1.67 (0.8)46 (2)32.5 min13.3 (0)0.41 (0)1.49 (1)48.5 (2.5)48.5 cm NH3 /13.3 cm HCl = 3.65x fartherNH3 than HClw/ pH paper (1) ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download