Wikipedia:Reference desk/Archives/Science/2019 October 14

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October 14

pH - actually math question.

So the pH scale is logarithmic, every unit in 1 is a power in 10. So from pH 7 to 6 is 10x more acidic 7 to 8 is 10x less acidic. How do you calculate what would be twice something acidic/basic? So ph 7, what's 2x acidic and basic, and how do you derive that? Thanks. 67.175.224.138 (talk) 00:55, 14 October 2019 (UTC).

pH = -log₁₀[H⁺] , where [] indicates concentration. pH 7 implies [H⁺] = 10^-7, so you can double that and plug it into the formula. Someguy1221 (talk) 02:01, 14 October 2019 (UTC)

log(10^7) = 7, and 2 log(10^7) = 14, so doubling it didn't help. 67.175.224.138 (talk) 02:33, 14 October 2019 (UTC).

You know what, I think I got it. -log( 2 * 10^-7) = 6.698...

And ............................ -log(.5 * 10^-7) = 7.301... 67.175.224.138 (talk) 02:42, 14 October 2019 (UTC).

Yep, log(2) = 0.301..., and thus the rule of thumb that a 3 dB change represents a doubling or halving. -- ToE 14:51, 14 October 2019 (UTC)

It's worth noting that while a 0.3 change in pH does represent a doubling or halving of concentration, and that matches your definition of being twice as acidic/basic, I don't know if "Solution A is twice as acidic as solution B." is something a chemist would ever say. (Can anyone here comment on that?) A 3 dB change in sound level represents a doubling or halving power, but it takes a 6 dB change for a doubling or halving of the rms sound pressure, and it is commonly held that it takes a 10 dB change for a double or halving of the perceived volume or loudness, a subjective perception.[1] If chemists do speak of one solution as being so many times more or less acidic than the an other, then perhaps they are doing so based on something other than the direct ratio of hydrogen ion activities. -- ToE 17:06, 14 October 2019 (UTC)

"Half as acidic" is either ambiguous or not used that way. If I take a 1 M HCl solution and dilute it 50%, I could say my solution is half as acidic (the solution is less-strong an acid). Dilute 1 M HCl by a factor of ten, and it's a tenth as acidic (raising one pH unit); by a factor of 100 raises it 2 pH units. But I don't think anybody would say that going from pH 6 to pH 8 is becoming "one hundredth as acidic" even though [H⁺] is reduced by a factor of 100...it's not a "weaker acidic solution", but is basic instead (even though it could act as an acid in the presence of an even stronger base). DMacks (talk) 17:22, 14 October 2019 (UTC)

I find your language confusing. I am used to strong/weak acid referring to the ease for the acid to release H+, that is, the pKa, not the pH. Gem fr (talk) 11:34, 15 October 2019 (UTC)

I was careful to include the word/concept of "solution"...the strength of a solution is obviously related to its concentration. You are right about the other idea obviously as well...the intrinsic acidity of the solute that makes the solution acidic (that's why I specified HCl, and specifically chose a strong acid). DMacks (talk) 12:04, 15 October 2019 (UTC)

Well when you add water to acid, that doesn't change the amount of H+ ions already in there, right, so the pH stays the same? Diluting it changes the pH? 67.175.224.138 (talk) 19:15, 14 October 2019 (UTC).

Yes, diluting change the pH (because it reduce the concentration, obviously). The pH will get closer to 7. Gem fr (talk) 11:27, 15 October 2019 (UTC)

Yup, pH is exactly related to concentration, not the numerical amount. Someguy1221 already said that in the very first reply to the original question. DMacks (talk) 12:04, 15 October 2019 (UTC)

Drug testing.

Since drug testing for urine, can determine whether someone does weed, cocaine, or various drugs, then can urine testing also determine whether someone ate food like broccoli, spinach, blueberries, or cherries? And don't you have to worry about false positives and false negatives, i.e., blueberries contains anthocyanins, but evidence of anthocyanins in urine doesn't conclude you ate blueberries. Can drug testing also tell what kind of meat you eat, like between beef, pork, and chicken? Thanks. — Preceding unsigned comment added by 67.175.224.138 (talk) 00:58, 14 October 2019 (UTC)

They likely could develop tests for specific foods, based on what metabolites and waste products make it to the urine, but I doubt if anyone has done so, as there isn't much need for it. SinisterLefty (talk) 01:45, 14 October 2019 (UTC)

Not all metabolites and not all metabolic pathways are created equally. Testing for alcohol consumption in urine might only give a positive result for the first few hours after consumption, while testing for marijuana might yield a positive result days, or even weeks after use. What's the metabolic half-life of these compounds? What's the limit of detection for the measurement technique (which also won't be the same for all compounds), and how does it compare with the actual expected concentrations in urine? It's not impossible to imagine some things might not be detectable easily at all. Certainly, even in the field of drug testing, there's a bit of a cat and mouse game (especially regarding performance enhancing drugs) between testers and drug designers. Meats certainly have some chemical differences between them, but are largely made of protein, and so their breakdown products may end up being too similar to discern either from each other, or from our own protein breakdown products. --OuroborosCobra (talk) 23:28, 15 October 2019 (UTC)

What is the method used for determining the metabolites in drug testing? Spectroscopy? 67.175.224.138 (talk) 00:31, 16 October 2019 (UTC).

It depends. Methods differ depending on the metabolite and what method has the best limits of detection and (if necessary) limits of quantitation. Note that for some drugs, positive/negative presence is all that is needed, as they are illegal substances and having them in your system at all is proof of crime. When it comes to other substances, like alcohol, you need a quantitative test that demonstrates whether one is currently intoxicated or not. One challenge right now for marijuana (at least as far as I am aware) is that we don't have a good test for current intoxication, since until recently, the legal status was fairly universally "any amount is illegal," and there was no need for a test for intoxication. Immunoassays are a common method, though possibly not the best for a quantitative result. Chromatography, sometimes combined with mass spectrometry, is another method. This article describes more on current urine testing techniques. --OuroborosCobra (talk) 01:09, 16 October 2019 (UTC)

Well, my specific question would be the urine testing that takes a few seconds. After giving the nurse my cup of urine, she dips some item in it that has like 8 tubes or so (for each test) and within seconds she records a positive or negative for all of them. Perhaps the positive/negative is a color change? 67.175.224.138 (talk) 01:20, 16 October 2019 (UTC).

That would be an immunoassay test, most likely. Sometimes that result is determined through a color change, but there are otherways (change in fluorescence, for example). --OuroborosCobra (talk) 18:56, 16 October 2019 (UTC)

Wow, I've never had seen/used/learned of immunisays and ELISA in any chemistry class, for analytics (did IR, NMR, GC, HPLC, etc.). What class in the biology department deals with immunoassays and ELISAs? Is it a different technique? I mean what would be the closest. 67.175.224.138 (talk) 20:55, 16 October 2019 (UTC).

We have a urine drug test article-section. DMacks (talk) 03:02, 17 October 2019 (UTC)

Bah, that doesn't answer my question either, as it mostly lists a list of metabolites that they are able to detect, but not say how. I see the article Urine_test_strip but doesn't seem to cover drugs? 67.175.224.138 (talk) 06:47, 17 October 2019 (UTC).

Yikes, that's a silly redirect. Why doesn't it point to the same place as urine drug screen, which is more on-target for you? DMacks (talk) 08:52, 17 October 2019 (UTC)

Here's a ref summarizing (among other things) what can cause incorrect results. I spot-checked the refs for the individual drugs and they often have quite specific technical detail about the individual test (because they are studying the scope and limitations of the test itself). DMacks (talk) 08:59, 17 October 2019 (UTC)

Color theory.

Has anyone attempted to combine the RGB theory with wavelength? Like green light for example, is rgb(0, 255, 0) and 555 nanometer in wavelength, but that doesn't necessarily convert? Then, take pink for example. Pink isn't on the electromagnetic spectrum (the Roy G. Biv). So how would 1 convert RGB(255, 192, 203) (pink) and find it on the electromagnetic spectrum? 67.175.224.138 (talk) 03:15, 14 October 2019 (UTC).

Pink is some color at all visible frequencies (white) plus more color at the red frequency. The RGB color map doesn't always map to one frequency, because many colors are a combo of frequencies, which our brains then "see" as one color. So, only the colors of the rainbow have single frequencies. Now, you could come up with an approximation of each color by using variable amounts of 3 frequencies, for red, green, and blue. In your example, that would be the max amount of red frequency, 192/255 as much green frequency, and 203/255 as much blue frequency. (Our perceptions of light aren't linear, so you might need to adjust the amounts.) But, of course, that's just one pink, and there are many different pinks. It might be better to do the reverse, and define colors by something universal in nature, like the color of sodium in the flame test, using whatever visible frequencies that produces as the definition of that color. SinisterLefty (talk) 03:27, 14 October 2019 (UTC)

Well, the article on Pink doesn't talk about it in the eye-perception level, but the Wikipedia article on purple near the top has something on when it hits rods and cones in our eye, the L-cone and S-cone for red and blue, and how purple light differs from violet. But I figured pink was just a combination mix of red and white light. But the red and white light cannot come from the same source? 67.175.224.138 (talk) 03:47, 14 October 2019 (UTC).

There are single pink lights, like this one: [2]. The colors can also be tweaked by coating the glass with something to block portions of certain colors. Of course, this is less efficient in that those blocked colors are turned into heat and waste electricity. One of the trickiest things to control is the color of lasers, as they only come in a few frequencies, and you can't alter the color by blocking certain portions of the spectrum with a coating, because they only have a single frequency to begin with. They use techniques to double, triple, or quadruple the frequency to increase the number of colors available. SinisterLefty (talk) 03:59, 14 October 2019 (UTC)

There actually are tunable lasers. DMacks (talk) 06:07, 14 October 2019 (UTC)

Interesting, but a lot more complex than just putting a colored coating on a white light bulb. SinisterLefty (talk) 06:14, 14 October 2019 (UTC)

Trying to represent a RGB colour value by a single wavelength is like trying to represent a three-note chord by a single note. Gandalf61 (talk) 08:46, 14 October 2019 (UTC)

This is as near an imitation of the visible range of spectral colors as your display device receiving RGB signals can achieve. Reading the articles Color vision, Color theory and the following links will help. We seldom encounter true Spectral colors that comprise a single wavelength within the visible range 380 nm (deep violet) to 740 nm (deep red). The human eye+brain is incapable of measuring wavelength but is evolved to obtain a perception of color when it receives any mixture of light wavelengths that differs from the case of neutral color Grey or White. Cone cells of the eye retina have 3 different spectral sensitivities, thus color perception is 3-dimensional. Two theories describe the perception process: trichromatic theory and the opponent process theory. Both theories are accepted as valid and the trichromatic theory is the basis for the Additive color or RGB color model that is successful in color CRT, LCD and projection displays. For digital representation in computer graphics files and displays and in HTML coding for web pages the achievable colors are expressed as an RGB triplet (r,g,b) that in a byte-oriented system allows 2²⁴=16,777,216 colors from (0,0,0)=black to (255,255,255)=white. However it is impossible for an RGB display to give a genuine spectral color because such colors lie beyond the Gamut achievable by practical RGB Primary colors.

The example of pink

Pink is very desaturated red. If we were mixing oil colors, stirring a couple of drops of red pigment into a can of white paint would provide pink. However in RGB coding we are adding lights not pigments and the code for pink could be arrived at as follows. Start from a 75% bright grey/white RGB(192,192,192) which allows a 25% headroom for adding color. A fair pink results from filling the headroom with red primary i.e. RGB(255,192,192). Visualize this as drawing a line on the RGB color space triangle from the D65 white point to the red primary corner, and picking the point on the line 25% length from white. The red primary is not far from (but definitely not exactly at) the spectral wavelength ~610 nm so we may think of that as the unreachable end target wavelength of further desaturation. However there is subjective acceptance of a range of pinks and the OP cites from the Wikipedia article RGB(255,192,203). That point is reached similarly except that instead of desaturating by adding only 25% red, the added light is 85.1% red and 14.9% blue. Our vector direction leaving the D65 white point is rotated clockwise slightly and we may imagine it pointing to a deeper, possibly infra- red wavelength 650 nm or more, which is even further beyond the gamut. DroneB (talk) 20:39, 15 October 2019 (UTC)

What type of owl is this?

What type of owl?

It is probably the most common type around here. Bubba73 ^{You talkin' to me?} 05:35, 14 October 2019 (UTC)

Is it not a Great horned owl? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:47, 14 October 2019 (UTC)

Yes, it must be. Thanks.Bubba73 ^{You talkin' to me?} 05:49, 14 October 2019 (UTC)

Sharp drop of agricultural carbon dioxide emissions since 2012/13

If this data is correct, can anybody here explain what exactly caused that sharp drop from 150 to 31 Mt in 2012/13?--Hildeoc (talk) 09:06, 14 October 2019 (UTC)

The data is not correct. If you select the option all greenhouse gases instead of only CO2, there is no drop, and methane doesn't show weird behaviour either. As CO₂ and methane are the main greenhouse gases for agriculture, this is internally inconsistent. I've sent the some feedback to the website, so hopefully they will correct it soon. Femke Nijsse (talk) 12:45, 14 October 2019 (UTC)

@Femkemilene: Thank you very, very much – especially for taking the courage and trouble to notify the publisher. That's great! (Would you mind informing me about the outcome? I'd be very interested in their response.) All the best--Hildeoc (talk) 19:07, 14 October 2019 (UTC)

I'll keep you posted if I hear anything back from the publisher. Femke Nijsse (talk) 20:38, 14 October 2019 (UTC)

For crying out loud, Femkemilene. It's wrong of course but it's just missing co2 data for those years.--TMCk (talk) 22:58, 14 October 2019 (UTC)

@TracyMcClark: Sorry, but I'm only a layman. What exactly are you referring to?--Hildeoc (talk) 12:42, 15 October 2019 (UTC)

is escape velocity real?

Does escape velocity really exist? What if a rocket maintains speed of 80 km/h till it escapes the gravity well?
I mean, i can understand an object without any mechanism to increase or maintain the speed will require a "escape velocity". But what if the rocket has plenty of fuel, and time? What if the person in charge of rocket says "doesnt matter how much fuel we burn, or time we waste; i will not increase the speed above 80km/h" In that case, would the rocket escape to space? And if no, why not, and what would happen? —usernamekiran(talk) 12:09, 14 October 2019 (UTC)

off-topic, unproductive discussion. Everybody involved got to present their opinions. —usernamekiran(talk) 05:54, 15 October 2019 (UTC)
The following discussion has been closed. Please do not modify it.
Have you read Escape velocity? ←Baseball Bugs What's up, Doc? carrots→ 12:32, 14 October 2019 (UTC) @Baseball Bugs: hi. Even though not at all helpful, your attempts to help others are commendable. Yes, I had skimmed the article before posting the question here. The second paragraph states: Escape velocity is only required to send a ballistic object on a trajectory that will allow the object to escape the gravity well of the mass M. A rocket moving out of a gravity well does not actually need to attain escape velocity to escape, but could achieve the same result (escape) at any speed with a suitable mode of propulsion and sufficient propellant to provide the accelerating force on the object to escape. Which was not much helpful to my query. But on the better side, you didn't call me a troll/vandal this time. Just on side note, one shouldn't be condescending/derogatory on Q/A forums while answering. —usernamekiran(talk) 16:42, 14 October 2019 (UTC) Usernamekiran, this kind of rudeness to Baseball-Bugs is not appropriate or attractive. The quotation from the article appears to me to answer your query precisely, so it was a reasonable reply to ask whether you had looked at the article. I am not sure why you did not understand it thus, but that is something that we could have explored if you had had a less combatative approach. Jmchutchinson (talk) 18:39, 14 October 2019 (UTC) @Jmchutchinson: Hi. I was not being combative. But honestly speaking I was trying to be uncompromisingly forthright while trying to remain polite. I apologise for not being able to put the original question correctly in words. —usernamekiran(talk) 05:54, 15 October 2019 (UTC) There was no indication that the OP had read the article. I just wondered if the OP had in fact read it, and if so, had found it as confusing as I did. ←Baseball Bugs What's up, Doc? carrots→ 21:23, 14 October 2019 (UTC)

Actually I think the passage is a bit problematic. It says the rocket "does not actually need to attain escape velocity to escape", but it does need to, of course. Otherwise it doesn't "escape" (to "escape" is to become gravitationally unbound to the mass in question).

It's just that the escape velocity keeps dropping, till eventually it is lower than the hypothesized constant speed.

To be fair, the author was probably thinking of the escape velocity as calculated at the point the rocket lifts off, and it's true that the rocket does not need to attain that speed. --Trovatore (talk) 02:26, 15 October 2019 (UTC)

By definition of the velocity, if you manage to maintain any positive speed (in an ITRF), you will eventually escape the gravity well. But doing so would consume much more fuel that giving a big boost at the start. In practice that would be impossible because the amount of fuel required is exponential, not linear, in the amount of energy you want to give to the payload. Tigraan^{Click here to contact me} 12:38, 14 October 2019 (UTC)

@Tigraan: thanks a lot. My doubt is totally cleared now. See you around —usernamekiran(talk) 16:42, 14 October 2019 (UTC)

You may be interested in reading our gravity loss article. -- ToE 17:08, 14 October 2019 (UTC)

You might be interested in our space elevator article. This would allow slow ascent, which would be more efficient because the low speeds wouldn't incur the huge aerodynamic drag of rockets. Then there's a balloon assisted rocket launch, which has a slow ascent phase followed by a rapid one. Or simply launching a rocket from atop a high mountain also has a bit of a benefit in saved fuel. SinisterLefty (talk) 17:17, 14 October 2019 (UTC)

A space elevator is even more efficient because the payload "steals" the planet/moon/etc.'s angular momentum as it ascends, thanks to the Coriolis force. This means the only energy required is that to lift the payload up the elevator. A rocket needs to both lift the payload and accelerate it "sideways" to orbital velocity. --47.146.63.87 (talk) 23:56, 14 October 2019 (UTC)

Escape velocity says:

For a spherically symmetric, massive body such as a star, or planet, the escape velocity for that body, at a given distance, is calculated by the formula

$v_{e}={\sqrt {\frac {2GM}{r}}},$

where G is the universal gravitational constant (G ≈ 6.67×10⁻¹¹ m³·kg⁻¹·s⁻²), M the mass of the body to be escaped from, and r the distance from the center of mass of the body to the object.

Solving for r with $v_{e}$ = 80 km/h and M = mass of Earth gives r = 1.61×10⁹ km. After cruising around 2300 years at 80 km/h you can turn off your rocket a little beyond Saturn and escape, if other masses are ignored. PrimeHunter (talk) 21:55, 14 October 2019 (UTC)

Yes. The escape velocity decreases the farther you are from the center of the massive velocity. Anytime your velocity exceeds the escape velocity for that distance, you escape. Bubba73 ^{You talkin' to me?} 02:27, 15 October 2019 (UTC)

You may also be interested in reading about the Oberth effect, which goes into detail about why it is more efficient for a chemical rocket to burn at the bottom of a gravity well. This is in the context of a flyby of a celestial object, but the same principles apply. Of course assuming you are literally taking off from the surface of the earth, there is atmosphere to deal with, but you know, in the context of spherical cow rockets... Someguy1221 (talk) 01:42, 15 October 2019 (UTC)

I like to observe this bit of rocket science formed a plot point in the 1963 comedy movie The Mouse on the Moon. In the movie, Prof. Kokintz points out (quite correctly) that because the Americans and Soviets are trying to reach the Moon with conventional rockets, they have to get there in a few days, whereas his own ship, with a more powerful supply of energy, can take its time for the journey. --76.69.116.4 (talk) 03:53, 15 October 2019 (UTC)

• Thank you very much folks. Your comments have been very much intriguing, and helpful. It is appreciated a lot —usernamekiran(talk) 05:54, 15 October 2019 (UTC)

References

Slightly salted peanuts for the squirrels

I throw some bird feed to the birds and also various nuts like filberts to the squirrels. It is all thrown out on a deck of our house. You should have seen the speed the squirrels do away with 2-3 pounds of nuts. I simply could never catch them in the act. I heard long time ago that birds should not be given anything salty and here I am compliant. I do have some supply of peanuts. I tasted them and found them slightly salty. Shall I give the nuts to the squirrels? Thanks AboutFace 22 (talk) 19:56, 14 October 2019 (UTC)

If you consider squirrels to be pests ("rats with bushy tails", as some have said), then you might think it's good enough for them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:22, 14 October 2019 (UTC)

Hard to be sure. Sodium is an essential nutrient, so they do need some. If they aren't getting enough sodium in their diet, a few salted peanuts may actually be helpful. But, if they are already getting too much sodium, from discarded french fries, etc., then the salted peanuts could be harmful. Also, it's possible the squirrels may remove excess salt from the outside of the peanuts, either intentionally or as a result of burying them and digging them back up later. SinisterLefty (talk) 02:52, 15 October 2019 (UTC)

Thank you, Sinister. This is a delicate question for me. Obsessed with helping the nature to survive, don't want to do any harm. Of course birds and mammals are different phyla, squirrels are more likely as us and perhaps they can tolerate some sodium chloride. AboutFace 22 (talk) 14:23, 15 October 2019 (UTC)

Hi AboutFace 22. According to sources, there are three problems with feeding peanuts to squirrels. Peanuts in general harm squirrels by filling them with a less nutritious food than their regular diet, leaving them less room for the food they really need. In addition, both salted peanuts and raw peanuts actively harm squirrel health.

1. Pest control company squirrelcontrol.ca says: "The two main issues with feeding squirrels are filling them up on foods that have little or no nutritional value or foods that are outright dangerous. Peanuts have little nutritional value for squirrels and salt is very bad for squirrels."

2. Pet food store nwseed.com says: "Salted nuts of any kind should never be fed to wild creatures." and "Feeding raw peanuts to squirrels and other animals can have serious consequences. The results can even be fatal. Peanuts when raw contain a trypsin inhibitor, a substance that inhibits or prevents the pancreas from producing trypsin which is an enzyme essential for the absorption of protein by the intestine. The detrimental effects on rodents have been documented since 1917. Thus squirrels fed a steady diet of raw peanuts could easily develop severe malnutrition."

3. Online magazine sciencing.com says: "You should feed a wild squirrel food that aligns with their natural wild squirrel diet [link provided] to avoid making them sick and/or overweight. Too many peanuts along with expired nuts can be dangerous for squirrels to eat. Peanuts for squirrels seems like a no-brainer, but they're actually not super nutritious." 70.67.193.176 (talk) 16:10, 17 October 2019 (UTC)