Your goal this lab period will be to figure out which solutions are in two sets of bottles, using properties or techniques discussed or experienced in the course or lab thus far (see below). As such, this lab will help you synthesize and apply knowledge/ideas you have been exposed to. You will not be told much in the way of specifics, except for what’s on this page. You will have no scripted procedure to follow. You will develop and execute a plan together with a partner or group (informed by your preparation beforehand; see prelab details below). The two Parts described below are separate experi-mental “puzzles” to be worked on one-at-a-time. Your group may start with either Part (assigned by your instructor), although by the end of the lab period, each group is expected to complete both Parts. NOTE: Groups are allowed to ask the instructor for any reagent / equipment / apparatus during the lab period, including samples of the “knowns”. However, you are expected to be able to describe what you plan to do with the equipment/reagents at the time you are asking for them. Ideas and Suggestions: 1) Bring your previous lab write-ups and text to lab. You may use them (as well as the web) as resources to help you determine means to differentiate between the substances/solutions in this experiment. 2) Also consider, in particular, the Hydrates experiment and the Alkaline Earth/Halogens experiment, as well as any demonstrations you’ve seen; you have used or seen many of these reagents (or ones like them) at one point or another during the course of lab or in lecture thus far, and we’re asking you to think about what you (or your instructor) did with them in the hopes that you’ll be able to use that knowledge to help you here. Note, however, that you should not limit yourselves to what we have done! Be creative and use resources! There are many ways to solve each of these “puzzles”! 3) Definitely review and seriously consider the solubility rules, and how you might add a solution of one compound to several others and get a precipitate or bubbles in one or more (but not all of them)! For example, think of what you did in Part I of the alkaline earth cations in a recent experiment, or the last part of the prelab for that experiment. Keep in mind that all of the substances listed below must already be soluble in water since you will be given aqueous solutions of them! Thus, you must think about what to add to them to cause a change in some but not in the others. 4) Since these are all fairly dilute aqueous solutions and not pure substances, determining density will not distinguish them! All will have a density very close to that of water! 5) Lastly, litmus is an acid-base indicator that is red or blue depending on whether a solution is acidic or basic. You have strips of paper containing this indicator in both forms (red and blue) in your lab drawers, and you might find that paper (called “litmus paper”) useful here. To determine how litmus paper responds when exposed to an acid or a base, you can simply do a quick experiment in lab! Just put a drop or two of some known solutions of acids or bases (just ask for such solutions!) on both kinds of paper! No need to look this up; if you’re in a laboratory, you can experiment to figure things out! I hope you will have fun with this.IMPORTANT: There will be one set of bottles in the lab for each experiment below with 1’s (e.g., 1A, 1B, etc.) and one set of bottles with 2’s (2A, 2B, etc.). Your instructor will assign you to do either the “1’s” or the “2’s”. Please make sure to write down which set you do in your lab notebook, and do not mix up the bottles!
Part IConsider the six bottles labeled A, B, C, D, E, and X. Exactly one of these bottles contains an aqueous solution of NaOH, one contains an aqueous solution of HCl, one contains an aqueous solution of HNO3, one contains deionized water, one contains an aqueous solution of Na2CO3, and one contains an aqueous solution of NaCl. Figure out which bottle contains which using any means (and equipment and reagents) you wish, subject to instructor approval. Safety must be considered!
Part IIConsider the six bottles labeled F, G, H, I, J, and K. Exactly one of these bottles contains an aqueous solution of AgNO3, one contains an aqueous solution of BaCl2, one contains an aqueous solution of NaCl, one contains an aqueous solution of C12H22O11 (sucrose; table sugar), one contains an aqueous solution of LiCl, and one contains deionized water. Figure out which bottle contains which using any means (and equipment and reagents) you wish, subject to instructor approval. Safety must be considered!
Prelab: Write down at least two possible actions you could perform during Part I, and another two possible actions you could perform during Part II (see below) to help you distinguish the contents of one or more bottles from the others in that set. That is, write down two experimental “tests” (something you could actually do) which will allow you to distinguish one or more of the substances/solutions from the others in Part I, and two “tests” which will allow you to distinguish one or more of the substances/solutions from the others in Part II. State clearly how your observations during your “test” will help you make some kind of conclusion about the contents of the bottles (e.g., don’t simply state “use the solubility rules” to determine cations X and Y). For example, if solutions of NaCl and NaOH were to exhibit fluorescence when exposed to a handheld UV-lamp (they don’t, so don’t use this in your prelab!), and the other solutions did not, you could write that you’d “Expose a small sample from each bottle to light from the UV-lamp. The two samples that fluoresce would contain NaCl or NaOH” (you wouldn’t know which was which yet, but you’d have made progress distinguishing them from the others). NOTE: You do not need to write a set of procedures to solve the whole problem in each Part! Just two specific “tests” to make some progress (i.e., distinguish one or more from the others) toward the ultimate goal in each Part.
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