1

Chemistry / Re: How many protons and electrons of C and Cl are in this compound?

« on: Today at 15:38:18 »

Every H atom has 1 proton and 1 electron
Every C atom has 6 protons and 6 electrons
Every Cl atom has 17 protons and 17 electrons

These are all conserved when the atoms come together to form (neutral) molecules.

2

New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 17/06/2019 21:09:23 »

Not everyone on this forum is an expert, certainly not in all topics discussed here. However, some of the members posting in this thread (including myself) are very well educated in QM. You would do well to try to understand what we are saying. Based on the types of assertions and confusions you (pittsburghjoe) appear to be making, and the great degree of confidence you appear to be displaying, I suspect that you currently reside somewhere near the top of "Mt. Stupid" (https://www.theengineeringmanager.com/growth/mount-stupid/)


Screen Shot 2019-06-17 at 4.06.15 PM.png (127.11 kB . 990x690 - viewed 548 times)

Don't worry, it is possible to scale back down (and to the right side), but it's a very disconcerting climb...

3

Physics, Astronomy & Cosmology / Re: Can tunneling work with gravitational potential wells?

« on: 15/06/2019 12:34:43 »

Tunneling amplitude is proportional to e^{–width of barrier}

https://en.wikipedia.org/wiki/Quantum_tunnelling

even empty space can be viewed as a barrier through which to tunnel.

Electric potentials within molecule-scale systems can have very high gradients, so the distances involved are small.

For gravitational wells, gradients are typically not very strong (except in the hypothetical cases mentioned by evan_au), so the distances are likely to be such that tunneling can only happen once every million universe lifetimes or so (not actually calculated, but you get the idea)

4

New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 14/06/2019 03:53:18 »

Mass has little to do with how big a slit something needs to get through... (so the proposed experiment can neither confirm nor challenge the notion that waves can have mass--spoiler alert, waves can have mass)

...but there is a somewhat nifty way to see that mass is important for calculating tunneling barriers for particles (which depends on the wave function treatment of the particles):

We can measure the rates of chemical reactions, and see how much they change when hydrogen atoms are switched for deuterium (chemically identical isotope, but with twice the mass). This is called the kinetic isotope effect (or KIE). Sometimes a hydrogen atom has to tunnel from one place to another for the reaction to occur, and sometimes (especially when the reaction is very cold) this is the rate determining step, which means that we can directly measure how long (on average) it takes for protons to tunnel from x to y, and compare with hoe long it takes deuterons to tunnel from x to y. When this tunneling is the rate determining step, the KIE is very large, sometimes even slowing down by a factor of 100 when doubling the mass of the tunneling particle. This means that mass is an important property of a quantum object, even when considering it as a wave.

https://en.wikipedia.org/wiki/Kinetic_isotope_effect#Tunneling

5

General Science / Re: Can you make a huge prism, and disperse light in different colors?

« on: 04/06/2019 02:45:57 »

I just found this reference online: https://www.nnin.org/sites/default/files/files/Karen_Rama_USING_CDs_AND_DVDs_AS_DIFFRACTION_GRATINGS_0.pdf

The CD peeling methods might be of interest to those, likeJMerrill, who wish to incorporate rainbows in artwork, and the equations shown might be of interest to those, like Colin2B, who wish to examine the mechanism of forming those rainbows--it turns out that one can even calculate the spacing of the ridges with some accuracy using a laser and a ruler (I am certain the error bars would drop if one used multiple lasers, each with a different wavelength...

6

Chemistry / Re: Does magnesium sulphate react with hydrochloric acid?

« on: 01/06/2019 21:48:41 »

And thanks @chris and @Colin2B 

7

Chemistry / Re: Does magnesium sulphate react with hydrochloric acid?

« on: 31/05/2019 15:10:50 »

In aqueous solution, there is no difference between a solution containing magnesium chloride and sulfuric acid, and a solution containing magnesium sulfate and hydrochloric acid, each just contains Mg²⁺ ions, H⁺ ions, Cl^– ions, and a mix of SO₄^2– and HSO₄^– ions (depending on pH).

Trying to precipitate out MgCl₂ selectively from this solution would be difficult, but not impossible (though yield and purity will be traded off--ie high purity probably only possible with very small yield, and high yield only possible with low purity).

With a sufficiently high ratio of chloride to sulfate, the solution could be cooled to selectively precipitate out MgCl₂. The ratios needed can be derived from looking at their respective K_sp values:
MgCl_2(s) Mg²⁺ + 2 Cl^– K_sp = 738 M³
MgSO_4(s) Mg²⁺ + SO₄^2–  K_sp = 4.7 M²

So if a starting solution has a 1:1 molar ratio of Mg²⁺ SO₄^2–, one can calculate just how much chloride would need to be added to favor precipitation of the chloride salt over the sulfate salt.

Based on the K_sp, saturated MgSO₄ is about 2.1 M. Plug that in to the MgCl₂ K_sp expression, and you will find that the concentration of chloride needed is about 18.7 M. The solubility of HCl in water maxes out at about 12 M, so you would need to cool and/or pressurize the system to accomplish this (I don't recommend actually trying this!)

Alternatively, you could add 1 equivalent of CaCl₂ to the solution, which will precipitate out as CaSO₄, which can be filtered off, and then evaporation of the water from the solution will leave MgCl₂.


I hope this isn't homework...

8

General Science / Re: Can you make a huge prism, and disperse light in different colors?

« on: 29/05/2019 20:15:39 »

The dispersion obtained from a CD (or similar) is due to diffraction. This can be verified by shining light with different spectral makeup on it and looking at the reflected patterns. If one has access to red and/or green laser pointers, one can easily see that a single laser point generates a whole diffraction pattern (multiple bright spots), and that the spacing of the diffraction pattern is different for red (typically 600-700 nm, depending on source) and green (typically 532 nm doubled Nd:YAG). One can also look at the "rainbows" produced from light from an incandescent source (continuous), and from fluorescent or LED lighting (a few narrow bands).

9

Physics, Astronomy & Cosmology / Re: Why don't atmospheric gases separate according to specific gravities?

« on: 29/03/2019 18:58:12 »

There is a very small amount of separation, but this is largely due to the fact that most of the gases that make up the atmosphere have very similar molecular masses (N₂ 28, O₂ 32, Ar 40).

The difference in gravitational potential energy that would occur by stratifying would be less than the energy equivalent of the decrease in entropy (due to unmixing) at the temperature that the atmosphere is. Same reason that vodka doesn't spontaneously separate into water and ethanol (which is about 20% less dense than water).

10

Chemistry / Re: Why would you burn coal, then turn the carbon dioxide back into "coal"?

« on: 07/03/2019 21:12:53 »

As far as I can tell evan_au's objection stands.

It doesn't really matter what is done with the "coal." I have worked on a few carbon sequestration projects myself--it really only works out if (a) the energy being used to capture and convert the CO₂ is 100% carbon free, and (b) if the product has value. There may be use in products from electrocatalytically reduced CO₂, but if you think of the carbon footprint required to generate the raw materials to build a CO₂-reducing plant on the scale needed to have any effect on the atmospheric composition, it is unlikely to pay for itself (in terms of net CO₂) before it breaks!

Photosynthetic organisms already capture and convert CO₂ far faster than we could hope to do it (in the next few decades, at least). Just look at the slope of the jags on the Keeling curve compared to the slope of the overall trend:

maunaloa_2004.gif (23.92 kB . 540x404 - viewed 1094 times)
We just need to focus on not burning the fossil fuels in the first place, and allowing the photoautotrophs to do the work (ie preventing deforestation, promoting reforestation, and promoting healthy oceans). As long as we can allow the downward parts of the jags to extend a little bit, and the upward parts of the hags to be a little less intense, we can return to a reasonable equilibrium pretty quickly.

There might be a tiny little nudge we can do technologically to speed the process along, but focusing money and attention on these sorts of "band-aid fixes" merely diverts it from the "severed jugular" that the actual problem is.

11

General Science / Re: Is there any science behind divining water or oil?

« on: 04/03/2019 14:59:11 »

Indeed--there is no reasonable physical mechanism to facilitate divining. There are no properly controlled studies to indicate that it works better than chance. Major corporations each spend (many) millions of dollars on devices that they use to find water and oil with--why would they opt to do that if a dude with a stick could do the same?

Divining/dowsing is fakery.

https://xkcd.com/808/

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12

Technology / Re: Why are Some Fridges Hard To Open Again Once Just Closed?

« on: 04/03/2019 14:52:23 »

I have noticed this before as well. I suspect it has to do with pressure:

Fridges don't have a perfect airtight seal, but they are pretty good.

Let's say that the fridge interior is kept at 8 °C (281 K), and the air in your kitchen is 24 °C (297 K), so there is a fairly significant difference between the two (otherwise you wouldn't need a fridge!). When you open the door, the air mixes--for the sake of argument let's say that the air inside reaches 22 °C (295 K) by the time you are ready to close it. Then when the door is closed, the mixing no longer happens, and the air inside begins to col rapidly (the walls of the fridge and all the stuff in it is still at 8 °C, and has a larger heat capacity than the newly replaced air. If the air inside then cools down to 10 °C (283 K) from 22 °C (295 K), then the pressure would drops to 96% of atmospheric pressure (283/295). Standard atmospheric pressure is 101.3 kPa, so the difference in pressure between the inside and outside would be about 4 kPa, or 4 Newtons per square meter. Thus if your fridge door has an area of 2.5 m², you would need to supply 10 Newtons of additional force to open the door (about the same as lifting a 1 kg weight). This isn't much, but it is significantly more than would be required to open the door in the first place. (There may be more at play, as this number does seem low--even increasing the temperature difference within reason only gains a factor of 2. Perhaps condensation of humidity in the air compounds the effect--the vapor pressure of water falls from about 3 kPa at 24 °C to about 1 kPa at 8 °C, so this would add another 50% to the 24-8 difference...)

If , however, instead of trying to open the door again right away, you give it a few minutes, there is enough time for the pressure to fall, and then more air is able to leak in, re-equalizing the pressures.

13

Chemistry / Re: Is there a way to separate the HCl from a mixture of salt and vinegar?

« on: 24/02/2019 01:29:08 »

Sodium chloride and vinegar will not be a useful combination for distilling HCl.

The pK_a of acetic acid (the acid in vinegar) is more than 12 units above the pK_a of hydrochloric acid (4.8 vs about –9), so the concentration of HCl could never be more than one trillionth of the concentration of acetic acid (and vinegar is about 5% acetic acid). Also, acetic acid and water are both fairly volatile, so you would probably just end up distilling water and then acetic acid, leaving sodium chloride behind.

It is possible to convert sodium chloride into hydrochloric acid by adding acid and distilling, if one uses much stronger acid with a much higher boiling point (and little to no water). I believe that sulfuric acid and phosphoric acid both would do the trick.

However, I should note that pure, hot, gaseous HCl is *extremely dangerous.* If you don't have the right equipment to condense it, or aren't working with enough ventilation, or something goes wrong, you could easily *permanently* damage your eyes and/or lungs. HCl can be purchased (in multiple concentrations), and this is a much safer way to get it (cold dilute aqueous solutions of HCl can still blind you, but at least you are unlikely to kill yourself with them...)

14

Chemistry / Re: If i dry-distil sodium acetate, will i get acetone?

« on: 23/02/2019 12:07:03 »

Chris has correctly identified that the oxidation state of a carboxylic acid (like acetic acid) is higher than that of a ketone (like acetone), but there is another problem with this approach--molecules of acetic acid have two carbons in them, and molecules of acetone have three carbons in them.

There are ways of converting acetate to acetone, but they are much more complicated and less efficient than envisioned by the OP.

15

Chemistry / Re: Can an electron have two orbital directions?

« on: 21/02/2019 20:46:55 »

m_l is the closest thing to an "orbit direction"

ie if l = 0 then there is no need to describe a direction
if l = 1 then m_l can be +1 or –1 or 0 (representing each of the axes that the spin could be about)
if l = 2 then m_l can be +2 or +1 or –1 or –2 or 0 (representing each of the pairs axes that the spin could be about) (this one is more of a stretch)

there is no reasonable interpretation of an m_n

16

Question of the Week / Re: QotW - 19.02.18 - Why does alcohol make you drunk?

« on: 18/02/2019 18:50:35 »

As far as I know, the exact mechanisms of alcohol intoxication are not known. However, it appears that the primary effects are related to potentiation of GABA pathways in the brain (so many of the effects are similar to those of benzodiazepines, GHB/GBL, gabapentin, and barbiturates, each of which potentiates or activates this pathway in different ways.)

Unlike these other drugs, especially benzos, which are quite potent and selective (a 2 mg dose of valium wouldn't be unusual), alcohol is very weak and unselective--requiring doses typically measured in ounces or deciliters!

As I understand it, activating GABA pathways dampens other signals in the brain--with the effects manifesting more strongly for processes that require more neurons (especially if thee neurons are in different parts of the brain). This means that just a little bit of alcohol can potentiate the GABA pathways a little bit, causing the most change in higher cognitive functions like reasoning and self-control. As the dosage increases, the effects there increase, and it also starts manifesting in fine motor control and response time. When really large doses are reached, even the ability to breath can be compromised.

Acute toxicity of alcohol (for a single large dose) can largely be attributed to loss of the ability to regulate breathing, or aspiration of vomit. But most injuries and deaths due to acute alcohol intoxication are due to loss of gross motor skills and response time, especially when it comes to things like automobiles and stairs...

However, much of the harm from alcohol is not from acute, but rather chronic abuse. Because the dosage is so high, alcohol is very hard on the liver and kidneys. Also, the neural pathways that alcohol acts on become resistant, then accustomed to and then dependent on the alcohol. Those who drink excessively for a long time can suffer from the potentially fatal DTs (delerium tremens), which can cause hallucinations and seizures (both of which can be treated with some of the GABA potentiators mentioned earlier).

17

New Theories / Re: How do we measure the energy of a photon?

« on: 07/02/2019 04:46:54 »

Space is curved by massive objects. Light goes "straight" within that space. This is very different from the force of gravity on other massive objects.

18

Chemistry / Re: How do I identify bridging Mo-O and terminal Mo=O in FTIR spectrum?

« on: 04/02/2019 22:10:24 »

The terminal bonds will have higher stretching frequencies than the bridging ones. I don't know off the top of my head where these will all lie, but based on Co-O and Co-O-Co vibrations, which I am more familiar with, I would expect bridging Mo-O-Mo vibrations to be around 300 cm^–1, terminal Mo-O-H to be more like 600^–1, and Mo=O might be closer to 1000^–1...

I am certain this info can be looked up. You can also model it using DFT.

19

Chemistry / Re: Can water be avoided in the Limestone cycle

« on: 29/01/2019 19:04:57 »

I don't know what the optimal amount of water would be (and it might be zero).

I think that sounds like the starting point of a great science fair project. You could either do tests with controlled atmospheres (in sealed air-tight containers) that have essentially no water in them, and possibly higher concentrations of CO₂ than air has, assuring that there is no reaction with water, and only with CO₂. Or you could test equal amounts of CaO in setups that are identical other than how much water is added first.

It might be difficult to measure how much CO₂ has been absorbed, but not impossible.

Good luck!

20

Chemistry / Re: Mercury, can you really safely dip your hand into?

« on: 29/01/2019 15:04:15 »

Yes. You can do it once or twice without any ill effect.

However, mercury is quite toxic. So how can this be?

Elemental mercury (ie the liquid metal) cannot easily pass through skin, so every time you touch it the dosage is incredibly small--each touch will deliver far less than a toxic dose. However, mercury is also very slow to leave the body, and can accumulate. This means that repeated exposure to small doses eventually adds up to a large dose.

Those who work with mercury on a regular basis without proper protection will be poisoned.

It is especially dangerous to heat mercury up, as it has a fairly high vapor pressure (for a metal--it boils at 360 °C). The vapors can condense in your lungs, and then will stay there until it has been absorbed (even though it is absorbed slowly, there isn't anywhere else for it to go, so you will get the whole dose).

Also, some compounds of mercury are MUCH more easily absorbed. Dimethylmercury is a notorious example. A single drop can pass through a rubber glove and through the skin within seconds, delivering a fatal dose (this has happened).