Wikipedia:Reference desk/Archives/Science/2013 October 3

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October 3

Sugar conductivity

During a chemistry lab experiment, my group was determining the conductivity of three unknown substances A, B, C (which we believed to be salt, sugar, and baking powder, respectively). We put 5 grams of each substance into 50mL of distilled water, and tested the conductivity of each separately (after washing the tester, of course). Despite our hypotheses, we found that substance B did have a slight conductivity, despite being watered down with distilled water and wiped clean. Later, I figured this was because, if B was indeed sugar, its polarity and dipole-dipole forces would play a part in making the water slightly conductive, while others thought it was just human error by not cleaning the tester well enough. Thoughts? Thanks! 174.93.62.131 (talk) 00:08, 3 October 2013 (UTC)

Perhaps because table sugar separates into sucrose and fructose at a certain rate in water? Been far too long since I did that experiment myself. μηδείς (talk) 00:26, 3 October 2013 (UTC)

Ash content of sugar is measured by conductance of the solution; refined sugar should have no more than 0.04% ash. Don't know how much this "ash" conducts, but you could assume it's salt and calculate the expected conductivity, see if it comes close. You did check the distilled water first? (should be about 0.5 to 3 µmhos/cm). Ssscienccce (talk) 01:01, 3 October 2013 (UTC)

The ash contains silica as a major fraction, however the remaining fraction is indeed an assortment of salts. Plasmic Physics (talk) 01:20, 3 October 2013 (UTC)

• The OP is essentially correct. Sucrose does have labile hydrogens, which will give it a very slightly ionic character. Also, even pure water will have a very slight conductivity due to the autoionization of water. Depending on the sensitivity of your conductivity test, either of these factors could give a small positive result. It probably wouldn't light a bulb, but if you have a sensitive meter, you may detect a very small current. --Jayron32 01:48, 3 October 2013 (UTC)

Yep. I would think autoionization would be the most likely explanation. DI water tends to run pretty acidic. A pH of 4 would give you a hydronium concentration, [H3O+] = 0.1mM. Not only that, you might have dissolved CO2 present in your DI water, which would further contribute to the ionic strength of your solution, since you'd make carbonic acid. (+)H₃N-Protein\Chemist-CO₂(-) 11:00, 3 October 2013 (UTC)

Purified water#Electrical Conductivity has some conductivity data for various types of "purified" water. DMacks (talk) 05:47, 5 October 2013 (UTC)

Space-time origami

Is it in theory possible to fold space-time, not just bend it? It would be a nice idea if space-time could copy electromagnetic radiation, by reflecting and refracting. I'd really want to see the straw in a glass of water effect without the water or air. What would be necessary to reallise this possibility, graviton beams? Plasmic Physics (talk) 00:33, 3 October 2013 (UTC)

We can answer your questions about known physics. What we really don't do here is write science fiction stories for you. --Jayron32 01:43, 3 October 2013 (UTC)

There is a sliver of an acceptable question in there, and one which now I wonder as well: Can spacetime "curvature" be non-differentiable? Someguy1221 (talk) 03:35, 3 October 2013 (UTC)

Are you talking about a discontinuity? Plasmic Physics (talk) 04:01, 3 October 2013 (UTC)

Because, if you are then that is exactly what I'm asking. Plasmic Physics (talk) 04:05, 3 October 2013 (UTC)

Not a discontinuity in spacetime, but a discontinuity in the rate of curvature. I'm not sure what you mean when you say "fold", but it made me think of the gridlines describing the shape of spacetime taking a sharp turn instead of gently curving. Someguy1221 (talk) 04:06, 3 October 2013 (UTC)

Is the question, "Can this happen in general relativity?" or "Is there a speculative framework in which it can fold/nondiff?" or "Does anything we know forbid this from ending up as the case in quantum gravity, etc?". I don't have an answer to any of them off the top of my head, but each is a very different question- also, what exactly do you mean by "fold"?Phoenixia1177 (talk) 04:24, 3 October 2013 (UTC)

There is a discontinuity in spacetime's curvature at the gravitational singularity at the center of a black hole. A non-rotating black hole just has a point singularity, but a rotating black hole, also known as a Kerr black hole, has a ring singularity along a circular line. However, the Kerr geometry may not actually exist in nature; the realistic gravitational collapse of objects into rotating black holes, and the resultant geometry, is an active research topic. Red Act (talk) 04:46, 3 October 2013 (UTC)

Origami involves folding paper without cutting or rejoining it, which has no effect from the perspective of general relativity, since it's only connectivity within the "paper" itself that matters. If you cut a wedge out of the paper and tape those edges together to get a cone then you have altered the connectivity of what's left of the paper. A straight cosmic string has a geometry similar to this, and if there was a straight cosmic string between us and a distant object (like a galaxy), we would see two identical images of the galaxy (see Cosmic string#Observational evidence). -- BenRG (talk) 13:23, 3 October 2013 (UTC)

Gravitational fields of massless particles. Count Iblis (talk) 15:13, 3 October 2013 (UTC)

All is helpful. Thank you. Plasmic Physics (talk) 08:11, 5 October 2013 (UTC)

Ionic bonds

I've come across a somewhat perplexing thought after a lab today, where we dissolved salt into distilled water. It took 52 seconds, longer than other substances like sugar, and it got me thinking. According to my chemistry notes, my textbook, and my teacher, ionic bonds are the strongest of intramolecular bonds (between atoms), and stronger than intermolecular bonds. The teacher explained how more energy is needed to separate the bonds, explaining why salt has such a high boiling point. However... when salt is dissolved in water, the sodium and chloride ions separate simply by being stirred in with water, but this takes considerably less energy to perform, no? If so, why does water make it to much easier to separate individual ions if their attraction is so strong? Thank you. 174.93.62.131 (talk) 03:23, 3 October 2013 (UTC)

I'm going to make a stab at it, it's most likely to be the solvation effect. Water molecules coordinate to the ions, stabalising the charge over a greater area, meaning that it is energetically favourable for the ions to separate into solution. Plasmic Physics (talk) 03:28, 3 October 2013 (UTC)

The rate at which a chemical change occurs cannot be inferred simply by knowing how energetically favorable the change is. Solvation of salt in water is far more favorable of a change than the solvation of sugar in water, but reaction kinetics are far more complicated than simply knowing how favorable a change is, and are generally difficult to predict from first principles. In the case of solvation, reaction rate is further complicated by the rate of diffusion of the solute from the (temporarily) solid mass, a factor which is mitigated by stirring (or "agitating" if we want to use chemist-speak). Someguy1221 (talk) 03:33, 3 October 2013 (UTC)

The OP didn't ask about the rate. They asked why water makes it easier for the ions to separate. Plasmic Physics (talk) 03:39, 3 October 2013 (UTC)

Sorry, i was just addressing the opening sentence, in case he was wondering. Someguy1221 (talk) 03:48, 3 October 2013 (UTC)

To answer the solvation part of the question, solvation can be conceptualized as three different processes working together:

1. Breaking the bonds between solute particles (i.e. separating the sodiums from the chlorides)
2. Breaking the bonds between solvent particles (i.e. separating water molecules from each other)
3. Forming new bonds between the water molecules and the solute particles

The first two steps are always endothermic (disfavorable) and cause increases in entropy (favorable), while the last step is exothermic (favorable) and causes a decrease in entropy (disfavorable). From a thermodynamic point of view, something will dissolve so long as the free energy (i.e. the sum of the enthalpy and entropy components of all involved processes) is negative. The reason salt dissolves, even though the bonds between the ions in the salt are very strong, is that in the end the bonds between the water molecules and the sodium and chloride ions are stronger, at least in the sense that the dissolved state is thermodynamically favorable vis-a-vis the undissolved state. --Jayron32 04:57, 3 October 2013 (UTC)

This article (Ion-association) should give you a rough idea. The dielectric plays a huge role on dictating the extent to which an ion pair will dissociate in a particular medium.(+)H₃N-Protein\Chemist-CO₂(-) 10:50, 3 October 2013 (UTC)

Equation

So... I'm making a poster, and for it I'd like to have an equation that relates (or at least tries to relate) sonwflake shape to the kinetics of its formation, can you help me? thanks in advance.--Irrational number (talk) 07:53, 3 October 2013 (UTC)

Well, there are fractals which look very much like snowflakes. You could include the equations to generate those. See Koch snowflake. StuRat (talk) 11:13, 3 October 2013 (UTC)

This paper contains a number of equations pertaining to the formation of real snowflakes; take your pick. Red Act (talk) 15:15, 3 October 2013 (UTC)

Concrete mixer truck

When a concrete mixer truck gets stuck in traffic for some hours and cannot deliver the concrete, could the concrete damage the truck? OsmanRF34 (talk) 22:00, 3 October 2013 (UTC)

Yes. I'd guess that SOP would be to dilute the concrete as much as possible and then pour a big pile at the side of the road. We run into similar problems when the electricity supply to the foundry gets cut. Lots of rock hammers and ear muffs for days. Greglocock (talk) 22:57, 3 October 2013 (UTC)

Another great opportunity to differentiate between what's probable and what's possible.

Normally, additives are included in the mix to delay setting. "How much" can be fairly easily estimated based on time in transit, ambient temperature, and so forth. Plus, you'll note that the mixer is slowly but constantly rotating, which also makes it more difficult to set up enroute.

But, is it possible? Sure, anything's possible given enough time, enough weird assumptions, and a bit of just plain bad luck. (What if the truck runs out of gas and can't keep stirring the mix, etc.)

And, if you're merely asking about does an extra hour of mixing abrade the lining of the mixer ... I don't know that one.

--DaHorsesMouth (talk) 23:04, 3 October 2013 (UTC)

No, I am asking about the truck not being able to deliver at all. Obviously, they'll try to avoid it, but I imagine that that could happen and in a big city. Dumping it won't always be possible. I thought that maybe some extra emergency additive could spoil the concrete on purpose and it would solidify (even if that would mean to through it away). OsmanRF34 (talk) 23:30, 3 October 2013 (UTC)

Concrete delivery trucks have a tank of water. If stuck in a traffic jam, the driver cand add water to the mix which, together with the agitation, will both retard setting, and make the set concrete weak. Adding water without agitation will not achieve anything. Don't know about the USA or other countries, dumping concrete on the side of the road in my locality would attract a huge fine for the driver, and possibly sanctions against the concrete company if it happened more than once. It will be much cheaper to, if necessary, sacrifice the mixer drum. Engine failure or running out of fuel is quite unlikely. A diesel engine idling in traffic consumes very little fuel compared to when travelling at speed. Incidentally, concrete trucks here used to have a separate 6-cylinder gasoline engine to power the drum. But some years ago, GM decided to cease supplying the engines to the truck manufacturers, so they changed to using a hydraulic rotation motor powered from a power take off (PTO) on the road engine. Much simpler, cheaper, and far more reliable. And eliminates the possiblity of leaving the depot without enough gasoline. 121.215.151.241 (talk) 00:25, 4 October 2013 (UTC)

Note that concrete mixer mentions the use of jackhammers and dynamite to deal with the situation. Wnt (talk) 00:37, 4 October 2013 (UTC)

Yes, but no reference for this is given. I'd like to know how the author thinks anyone could get in inside a space that small and use a jackhammer, or even drill some holes to place dynamite. The hole down the middle between the mixer plates is about large enough for a 12 year old at most to crawl down. About as likely as being randomly assigned $10,000,000 from a bank official in Nigeria I reckon. What is far more likely is that the driver takes the whole lot back to the depot, they remove the barrel/drum from the truck, cut up the barrel with an oxy-acetylene torch to expose the set concrete, then break that up with jack hammers. Meanwhile, a new barrel would have been installed on the truck. It's only sheet metal anyway. Barrels have a forward access plate secured with bolts to facilitate cleaning, but that won't do any good if the whole load has set. 121.215.151.241 (talk) 01:40, 4 October 2013 (UTC)

Removing concrete from the agitator bowl of a concrete truck with a jackhammer is a standard procedure in the industry, called "chipping"[1] or "de-dagging".[2] There are even companies that specialize in performing that procedure.[3] Red Act (talk) 02:15, 4 October 2013 (UTC)

I learn something new everyday - and here I stand corrected. They must use special small men or midgets and tiny jackhammers. However, the thrust of your second citation (a website of a company that cleans the barrels) is essentially, this is very very dangerous method, so don't do it unless you really really have to, and then you need to treat it as confined space per the Confined Space Act, which means a man outside doing nothing but keeping watch, and you must have a written plan to cover safety, communication, and person extraction aspects. Elsewhere in that website it says that they don't ever do it by entering with jackhammers. They use machine directed high pressure water nozzles. A link at the botton of your second citation links to a Govt safety authority, Worksafe Australia. They actually forbid men entering the barrel, and suggest using high pressure water. That will not always work - in such cases the solution I gave above seems to be the only reasonable approach. Next time I have some concrete delivered, which is part of what I do as an engineer, I'll ask a driver what he thinks/knows. The website you cited in your third reference gives no clue as to how they do it. 121.215.151.241 (talk) 03:09, 4 October 2013 (UTC)

(EC) Various sources [4] [5] [6] seem to confirm a jackhammer is used for cleaning the inside of a concentre mixer. These seem to be mostly referring to buildups rather than a full load, but it also seems clear from these sources people do go inside the concentre mixer without opening it for cleaning so I'm not sure your argument that the opening is too small holds. This source [7] other than confirming the jackhammer bit further (and also the going inside), also makes it clear someone tried dynamite once. It suggests it didn't work well for them, but it wouldn't surprise me if despite the source making it sound like they're the fountain of all learning in the field, that others have implemented and use it more successfully. That source also suggests they do deal with full loads and while it isn't entirely clear it does suggest they use jackhammers for the purpose. Considering the price given in that source $0.09 per pound (USD I presume), it's perhaps not surprising. The bowl/mixer may 'only' be sheet metal, but I'm guessing a new bowl could easily cost well over $5000 [8] [9] (even taking in to account what you recover from the metal). Yet as per article Concrete mixer and other sources [10], a full load is only likely 40k pounds or so meaning the price for this real world commercial company cleaning a full load (~$3600) will be well under a new bowl cost. P.S. From the sources it's apparent the cleaning was feature in an episode of List of Dirty Jobs episodes. From our article, I think it was in "Termite Controller" with a follow up in "Tight Spaces 2". Nil Einne (talk) 03:20, 4 October 2013 (UTC)

Reading our article more carefully, it actually mentions Mythbusters tried to use dynamite. While they also evidentally had little success, I've never been that impressed with the quality of Mythbusters experiments and it wouldn't exactly surprise me if they made a poor attempt at what someone else with the expertise regularly does. Of course it also wouldn't surprise me if the use of dynamite is indeed a complete myth which someone added to our article. I'll tag the claim in any case. Nil Einne (talk) 03:48, 4 October 2013 (UTC)

(This reply after reading the ECs above.) I found someone with these Dirty Jobs shows so had a look. While I obviously can't upload anything to wikipedia or associated sites, I do belief a small number of shots would be resonable under US fair use law so have uploaded them here [11] although if you disagree feel free to remove the link. It's obviously not that easy to get in but isn't that hard (for the host who's not a "midget") and this concrete mixer looked to be a small one. I'm not sure this was a full load but it looks to be more than simple build up. Of course this is the host and there's I presume a camera person inside so nothing here is necessarily typical but I would presume the jackhammer is one they would normally use in some cases. The host does mention it's fairly claustophobic but not simply because of the confined space but also because of the sensory deprivation due to the ventilator plus eye and ear protection plus sensations from the jackhammer although none of these would be unique to working inside a concrete mixer. BTW my impression from the links is that at least in parts of the US, using a jackhammer is still quite common. While there are those who promote different methods, I presume different health and safety and other requirements means different practices in different localities, as with many things. I would also note that while this is obviously quite a dangerous job with several risks, the fatality examples given by the Australian vendor above ([12]) while obviously saddening, seem to actually relate to poor work practices namely failing to properly secure the barrel beforehand rather than the dangers of the job itself when carried out in a resonable manner. Nil Einne (talk) 07:33, 4 October 2013 (UTC)

I've certainly learnt something new today. So men certainly do get inside and use jackhammers. The jackhammers indicated are definitely small ones though. Also, you are right, all your references are about removing concrete films built up during normal use, not a full load as relavent to the original question. I certainly would not disagree with your estimate of the cost of a new drum/barrel. But that's still a lot less than the fine a road-side dump would attract. Not fogetting that the authorities would probably make the driver/company remove the dumped concrete and make good any roadside surface or grass etc - which could also cost roughly around $5K. 1.122.115.40 (talk) 11:01, 4 October 2013 (UTC)

Slightly off topic with the original query (though Osman mentions "some extra emergency additive") but I recall that a way to stop concrete setting, or at least greatly delay it was to throw a few kilograms of sugar in to the mixer. Yes, here's a source mentioning it15 to 20 pounds of sugar. "concrete with that much sugar in it would never set up. I would lose the concrete but save the mixing drum". Apparently Coke works too (not Diet I imagine!) -ӄ- 220 of ^Borg 06:51, 4 October 2013 (UTC)

You have triggerred a memory of when I was studying engineering at University several decades ago. Salt will also render concrete extremely weak. But where is a concrete truck driver goig to get 20 pounds or so of sugar or salt in when stuck in a traffic pileup? 1.122.115.40 (talk) 10:45, 4 October 2013 (UTC)

In the cab of the truck or some other similar storage location? Since we're obviously talking about an ordinary emergency measure I would assume if anything was done or could be done, the driver could be trained for such an eventuality and for something like sugar or salt which is relatively harmless, it could be stored without issue (well for salt you might need special measures if it's a lab in NZ but I'm not sure those would apply to a concrete mixer). If these are not done, I presume it either because they're not very effective or they don't want the truck driving messing with the concrete and the risks and problems that entails. Speaking of safety, I'm not sure encourage the driver to add stuff to the concrete in random places, particularly in the middle of traffic even if it's stopped would be considered a good idea. (In other words, it doesn't seem storage or locating the salt or sugar would be a problem.) The other alternative would be installation of a special device to dispense the concrete that can be operated, perhaps from without the cab. However that sort of thing may get to the level of added cost and complexity that it won't be worth it, particularly given the risk of such a device failing and screwing up the concrete without anyone noticing until it's a bit late. Nil Einne (talk) 13:10, 4 October 2013 (UTC)