Hypothetical Chemist

Ok, just for fun, I'm going to pose a hypothetical puzzle of sorts that I thought up this morning, in order to see if you guys/gals come up with the same set of solutions that I did (pun intended):

<strong>Scenario:</strong><hr />You are seated at a glass table. Two clean empty 500 mL Kimax beakers are placed side by side in front of you. A lab technician proceeds to pour, from an unmarked PTFE bottle, ca. 300 mL of a clear colorlous liquid into the beaker on your left<!--HCl-->. She then pours ca. 300 mL of a clear colorless liquid from an identical bottle into the beaker on your right<!--NaOH-->. You are told that one of the bottles contains 1 M HCl (<em>aq.</em> and the other contains 1 M NaOH (<em>aq.</em>. You are provided a 10 cm length of plain borosilicate glass tubing with a circular cross-section (average diameter/bore, not capillary), flame-polished on both ends, to do with as you please. You are asked to determine which beaker contains which solution.<hr />
<strong>Constraints:</strong>
-You are not allowed to move the beakers.
-You are neither provided nor allowed any other chemicals, reagents, equipment, instrumentation, etc. other than that outlined above.
-For the purposes of this hypothetical scenario, your olfactory senses have been nullified (perhaps you were huffing H₂S?). No taste/smell.
-You are not permitted to apply solution to your corneas in order to determine which does the most damage (sorry).<!---dissolving hair
+slippery vs. 'rubby'
+evaporation residue
-drink contents
-'bead'
+/-optical refraction
+adherence to glass
-viscosity
+bubbling carbon dioxide
-ask the technician which is which
-dissolve a hair-->

<strong>Notes:</strong>
-The scenario and constraints may be subject to slight alteration, as I was away from the computer when I thought of all this, and I may have forgotten something.
-No cheating! Use your existing knowledge... please don't use search engines.

[Edited on 3/2/13 by bfesser]

You could just wait as long till one beaker got dissolved by the NaOH..
Nah, second way I would go is to get one drop out of both solutions and place it on the glass table. To one drop on the table you now add a drop of the other solution. As expected you get a neutralisation, but you don´t know which beaker contains what chemical. So take your rod and blow air with you mouth in both beakers for like 5 minutes and now take a drop from both solutions and place them on the table.
You previously reacted the NaOH with the CO2 in your lungs to NaCO3 or NaHCO3. So now you´ll have to wait till both drops are evaporated, and the drop which leaves a residude was from the beaker containing NaOH-solution.

1) I'd put one drop to my tongue and give it a taste. It will sting a bit, but hey, corneas are forbidden, tongues are not.

2) Smearing few drops of the solution between my fingers. NaOH will be more slippery.

3) This might not work, but it's worth a try. Equimolar solutions f NaOH and HCl at exact temperatures have slightly different densities. NaOH is 1.04 g/cm3, and HCl is 1.017 g/cm3 @25 °C, but the numbers are not important, the difference is.
I don't know if it would work with 1 M solutions because that's quite dilluted, but one could try picking up some of the solution A with th tubing and then drip it into the second beaker while observing how light bends. If the bending "blob" sinks, the drop is NaOH and if it kind of floats, it's HCl. I've never tried it, but it should work with high enough concentrations. 1 M might not be enough, but hey...

4) NaOH should wet the glass more than HCl, but that might not be visible enough for 1 M. So, I don't know.

5) If you snap the tubing and then score itself with the snapped piece to make a fine, dusty mark. Then you let each scored piece sit in its solution for a day. Unlike 1 M HCl, 1 M NaOH might do something about the score, but I really don't know for sure.

Smell them. HCl will be very distinctly different from NaOH
And again, pour some on a finger of both of your hands to see which one turns your skin soapy.

<strong>DraconicAcid</strong>, well done. My initial solution was to simply dip an index finger in each solution, and then rub together with thumb. The slippery one indicates the NaOH. The glass tube was not necessary for this test.

<strong>Simbani</strong>, there would not be enough NaOH in the solution to dissolve through the beaker. Nice try, though. You were on the right track with exhaling CO₂ into the solutions.

<strong>Endimion17</strong>, tasting was disallowed, remember? For the sake of simplicity, 'stinging' counts as a taste, not a damaging effect on the cells/nerves of the tongue, or whatever actually causes it. As for adding one solution to the other dropwise and observing the refraction caused by concentration gradients, they will react to form NaCl(<em>aq.</em>. I thought of this, but am not exactly sure it would work. Perhaps someone could actually perform this experiment (1 M solutions!) and record a video for us. I also came up with the glass wetting solution&mdash;quite elegant, nice work! I did think of trying to powder the glass by grinding on the table, but did not think of snapping the tube and using the break to score the other piece. That should work. Wonderful.

<strong>kuro96inlaila</strong>, I did not think of your idea. I'm not sure it would work, but it's another elegant solution. Nice work.

<strong>elementcollector1</strong>, smelling is disallowed. 'Soapiness' already repeatedly suggested. Did you <a href="http://en.wiktionary.org/wiki/TL;DR#English" target="_blank">TL;DR</a> <img src="../scipics/_wiki.png" />?

<strong>plante1999</strong>; hilarious! Perhaps for humor's sake, we'll allow AJKOER any hypothetical chlorine reagents he desires.

<strong>UPDATE:</strong>
There are four more solutions on my mental list that haven't been suggested yet. Keep them coming. You've got five of my ten, plus one I didn't think of.
Since suitable answers have been given, in my mental hypothetical, the beaker on the left contained HCl, and that on the right, NaOH&mdash;not that it matters.

[Edited on 7/9/13 by bfesser]

<strong>Progress (in no particular order):</strong><ol><li>soapy feel on skin (NaOH)</li><li>evaporation residue (NaOH/Na₂CO₃</li><li>adherence to glass (wetting)</li><li>exhaling into solution (several variants)</li><li>refraction of light (Endimion17's suggestion was close enough)</li><li><!--dissolve hair-->???</li><li><!--drink one-->???</li><li><!--'bead'-->???</li><li><!--viscosity-->???</li><li><!--ask technician-->???</li><li type="circle">vertical displacement by CO₂ absorbtion (nice one, kuro96inlaila!)</sub></ol>

[Edited on 3/2/13 by bfesser]

Solution 6: Pee a little on the table and allow the urine to get old and stale for a while (keep it warm for best results ) in order to get some ammonia. Then take a drop of liquid from both beakers and keep that above the old pee with the ammonia smell. The HCl will give off faint smoke, the NaOH does not. The reaction will not be strong with 1 M HCl, but one definately can see faint smoke of NH4Cl.

[Edited on 2-3-13 by woelen]

<strong>Diablo</strong>, you essentially guessed number six on my list. I often catch myself pulling out my hair while doing chemistry... though not for this reason!

<strong>woelen</strong>, I must admit, the thought of using urine crossed my mind. I didn't think it was worthy of inclusion into my list of ten, as the results may be hard to judge. I guess I should have included it. Let's make that number 11. Nice work. Perhaps you'll be willing to try this one and post it on your site?

<strong>Progress (in no particular order):</strong><ol><li>soapy feel on skin (NaOH)</li><li>evaporation residue (NaOH/Na₂CO₃</li><li>adherence to glass (wetting)</li><li>exhaling into solution (several variants)</li><li>refraction of light (Endimion17's suggestion was close enough)</li><li>dissolve hair (Diablo suggests NaOH straightening curly hair)</li><li><!--drink one-->???</li><li><!--'bead'-->???</li><li><!--viscosity-->???</li><li><!--ask technician-->???</li><li>urinate on table/in beakers (leave it to woelen...)</li><li type="circle">vertical displacement by CO₂ absorbtion (nice one, kuro96inlaila!)</sub></ol>
Four to go! Overall, I'm very impressed by the creativity and resourcefulness of some of these answers! If you blokes enjoy this, maybe I'll try to think of other puzzles like this.

Well this is a bit far fetched but you could knock out two teeth and place those into the solutions and wait for the other one to dissolve

EDIT: Well you could do it with only a one tooth as well..

[Edited on 2-3-2013 by kavu]

Here's a small modification of the wetting procedure... I've took the photo on my table few minutes ago.



NaOH should climb higher. Now, again, I don't know if 1 M is enough.

Also, drops of the solutions sliding down the glass, bases should behave differently as they adhere to the glass more than acids.

The blood thing came to mind, but it's kind of invasive... And I'd probably start feeling woozy because I can't stand to see my body leaking from its primary coolant circuit. °_°

It would be interesting to test whether humans could distinguish the sound given by glass rod banging on the beakers with fluids which densities vary so little. Probably not, and the experimental error would suffer a lot because of minute differences in beakers so any slight effect due to different fluid densities would be hidden. But it's a nice thought.

Regarding the light diffraction, yes - we're left with Na⁺ and Cl^- and H₂O, but that's after proper mixing. In the first few moments the blob is solution A in solution B, surrounded by a diffusing area of products. Someone should test whether 1M solutions really do show visible diffraction and floating/sinking. I think it should be visible under optimal lighting conditions.

[Edited on 2-3-2013 by Endimion17]

Quote: Originally posted by neptunium

NaOH solution freeze below 0c between 1 and 18% (by weight) HCl sol, will freeze way below that (25% by weight freezes around -80c) so if you can drop the temperature in the room the first solution that freezes is the NaOH one

No, the freezing point of a solution has its own value according to concentration AND nature of what is disolved in it.
even at same concentration the freezing and boiling point are different for each chemical. (in solution)


HCl freezing point

NaOH freezing point

Not sure if this counts as "extra chemicals", but you could regurgitate the red cabbage soup you ate for lunch (filter if necessary ) and add some to each of the beakers. IIRC, the HCl will go red, and the NaOH yellow/green?

Quote: Originally posted by Eddygp

Quote: Tear out a strip of your trousers and but each end in one of the beakers. The HCl and the NaOH would hopefully go up because of capillarity, and they would react forming NaCl nearer the NaOH beaker (well, I don't know how to describe it, but you can tell the difference). ... Would it work?