Wikipedia:Reference desk/Archives/Science/2019 February 20

= February 20 =

Balance Equations
Hi. (Grade 10 chem)How do I do a skeleton and a balance equation? -- Thegooduser  Life Begins With a Smile :)  🍁 00:16, 20 February 2019 (UTC)


 * Chemical equation has a section on balancing equations. Chemical structure is the worst article, given its importance, that I have seen on Wikipedia in years, but skeletal formula is better and more directly useful for your needs.  You can add particulars here to get more detail as needed. Wnt (talk) 01:53, 20 February 2019 (UTC)
 * In short, you assign an equation for each element in the formula, and then solve using simultaneous linear equations. For example, Z[C6H12O6] + Y[O2] -> X[CO2] + W[H2O], gives 6Z + 0Y = 1X + 0W; 12Z + 0Y = 0X + 2W; 6Z + 2Y = 2X + 1W.   These are for C, H, and O respectively. You then solve these equations by substitution, and find the lowest integer solution. LongHairedFop (talk) 19:09, 21 February 2019 (UTC)
 * Rewriting LongHairedFop's method more clearly, the W,X,Y,Z are the stoichiometric coefficients--the "how many of each chemical to make the equation balanced"--you are trying to find. And the resulting equations that so you have to solve to balance each element using them are:
 * {|class="wikitable" style="text-align: center;"

!rowspan=2 |Element !colspan=7 |Equation !Z[C6H12O6] ||+ ||Y[O2] ||→ ||X[CO2] ||+ ||W[H2O] !C !H !O
 * 6Z ||+ ||0Y ||= ||1X ||+ ||0W
 * 12Z ||+ ||0Y ||= ||0X ||+ ||2W
 * 6Z ||+ ||2Y ||= ||2X ||+ ||1W
 * }
 * DMacks (talk) 19:43, 21 February 2019 (UTC)
 * Thanks Dmacks, for clarifying that. Just to add, Thegooduser, that your Maths teacher will hopefully already have taught you simultaneous equations, which end up with absolute values for W, X, Y and Z. However, here we will end up with a ratio connecting W, X, Y, Z. The process is the same though. LongHairedFop (talk) 20:40, 21 February 2019 (UTC)


 * Simultaneous equations is the right answer. But students at your level often use the stopgap of simply writing out the numbers of atoms (or ions, if they know what they are) and multiplying by small numbers until they line up.  Usually that doesn't take forever.


 * For example, C6H12O6 + O2 -> CO2 + H2O would be written
 * {| class="wikitable"

!C !H !O
 * 6
 * 1
 * 12
 * 2
 * 8
 * 3
 * }


 * then the C on the right is changed to 6 by making it 6 CO2, which also increases oxygens


 * {| class="wikitable"

!C !H !O
 * 6
 * 6
 * 12
 * 2
 * 8
 * 13
 * }


 * then the H on the right is made 12 by making it 6 H2O, which raises the O also


 * {| class="wikitable"

!C !H !O
 * 6
 * 6
 * 12
 * 12
 * 8
 * 18
 * }


 * and then at last on the left the O2 is changed to 6 O2, which makes everything balance out. To be sure, of course, this is solving simultaneous linear equations, by a blind method that is easily hung up in fractions, but for the beginning student this can be more appealing at first. Wnt (talk) 03:11, 22 February 2019 (UTC)
 * Using half reactions is another method that is usually taught a lit bit later in introductory chemistry courses. Redox gives better instructions on how to use the method.--Wikimedes (talk) 16:33, 25 February 2019 (UTC)

Why does only human being cuts off the umbilical cord?
Why does only human-being cuts off the umbilical cord? If almost all mammals have an umbilical cord, so what's the reason that only the human being cuts it off? 93.126.116.89 (talk) 05:11, 20 February 2019 (UTC)
 * Because the other animals don't know how? 2601:646:8A00:A0B3:7177:1C34:7814:8A72 (talk) 05:16, 20 February 2019 (UTC)
 * Because only humans have blades, and like tidyness. If not cut off, it takes in humans about 3 days before the umbilical cord dries up and drops off, which would be an inconvenient span to cart around the attached placenta: in other species the time may be shorter – for example, 1 day for Chimpanzees.
 * Some other mammals bite through it, sometimes in the process of eating the placenta, which in humans is not the predominant practice but is not unknown, though it is usually detached and prepared in some way first. {The poster formerly known as 87.81.230.195} 2.122.1.40 (talk) 07:50, 20 February 2019 (UTC)
 * Ah, yes. Placenta Helper. - Nunh-huh 08:10, 20 February 2019 (UTC)
 * I don't understand; we cut off the umbilical cord just because we don't have a patience to wait 3 days? Or maybe there are some risks if it remains these 3 days before it dry up and drops off by itself (for example more probability for infections or other health conditions)? 93.126.116.89 (talk) 22:44, 20 February 2019 (UTC)


 * Mammal also clean their newborn intensively by licking and instinctively eat the remains of the Placental (also called afterbirth) so they actually manage a similar cleanup and care like humans. --Kharon (talk) 23:07, 20 February 2019 (UTC)

Mountain view (not in California)
Suppose you were flying in a plane, roughly on a direct course from New York to Albuquerque, at an altitude of about 1000 feet AGL (also suppose for the sake of the argument that the plane in question has unrestricted visibility in all directions, that you have a telescope with unlimited magnification, and that the atmosphere itself is perfectly transparent, so that neither atmospheric visibility nor your own visual acuity limit your range of vision, the only limitation being the horizon) -- under these conditions, at what point can you first see the Rocky Mountains through your super-telescope? Would you be able to see them by the time you fly over St. Louis? 2601:646:8A00:A0B3:7177:1C34:7814:8A72 (talk) 05:27, 20 February 2019 (UTC)
 * The distance at which a mountain comes into view is $$d\approx\sqrt{2aR}+\sqrt{2a_mR}$$ where $$R\approx6400$$ km is the radius of Earth, $$a\approx10000$$ m and $$a_m\approx4500$$ m are the altitudes of the plane and of the mountain, respectively. So, the result is about 700 km. Ruslik_ Zero 08:14, 20 February 2019 (UTC)
 * The equation solves the horizon distance. LongHairedFop (talk) 21:09, 20 February 2019 (UTC)
 * The above formula is correct, the numbers are not. The plane is at only 0.3 km above the ground and the mountain peaks in that part of the Rocky Mountains reach to about 2.8 km above the plain, which itself is at about 1.2 km above sea level near the Texas/New Mexico/Oklahoma tripoint. So that gives a distance of about 250 km. You'll see Wheeler Peak whilst flying over Texas Panhandle. That's ignoring refraction, which may allow you to see the mountains from slightly farther away. PiusImpavidus (talk) 09:46, 20 February 2019 (UTC)
 * Thanks! So this would happen when coming up on Amarillo? 2601:646:8A00:A0B3:7177:1C34:7814:8A72 (talk) 13:23, 20 February 2019 (UTC)
 * This is not to detract from the helpful answers given by others, but I'll try to help calibrate your intuition. The U.S. is big, almost as large in area as Europe. Missouri alone is about three-quarters the size of the UK. St. Louis is on the state's eastern border. If you can't see Scotland from London, even with a telescope, you're not going to see the Rockies from St. Louis. Being at 1000 feet will make little difference. If you're a fellow Californian, a more familiar comparison: you can't see the Tehachapis from the Bay Area, and these are still closer than St. Louis and the Rockies.
 * As for the longest line of sight on Earth, well, looks like we don't have an article! A brief Web search seems to indicate disagreement. Apparently the Guinness Book of World Records claims it is 550 km between Slættaratindur and Vatnajökull due to atmospheric refraction, but a lot of people question the veracity of this. --47.146.63.87 (talk) 02:33, 21 February 2019 (UTC)

What could happen when one doesn't tie the umbilical cord after cutting off?
It's interesting to me what could happen when one doesn't tie the umbilical cord after cutting off? Is the blood can come out of the baby (bleeding) or it's for reasons of infection prophylaxis? I checked out the article here, but I didn't find an answer for it.93.126.116.89 (talk) 23:58, 20 February 2019 (UTC)
 * See which links to lotus birth (note: some images contain nudity and a kind-of-yucky-looking placenta). As those links state, cord clamping and removal are done to prevent infection. Once the placenta is expelled, it's dead tissue connected to a healing wound (the umbilicus), which gives a great pathway for infection. --47.146.63.87 (talk) 01:52, 21 February 2019 (UTC)
 * Thank you for the comment. I learnt something new:) What about the bleeding from the umbilical cord? If it's not tied, then it bleeds? I'm asking to understand what happens from the side of the baby's belly. It says, if it's tied for reason of infection or reason of bleeding. 93.126.116.89 (talk) 02:58, 21 February 2019 (UTC)
 * It doesn't normally "bleed", if by "bleeding" you mean blood leaving the cardiovascular system. The umbilical cord in humans contains two arteries and one vein. In the womb, the baby's blood flows through these to and from the placenta. After birth, the cord begins to shrink and clamp shut to occlude the flow of blood. Tying it off hastens this, and serves as a "backup" in case things don't go as they should. Tying of the umbilical cord, then, serves both of the purposes you mentioned: to stop blood flowing into the cord and placenta, and to hasten the natural "dropping off" of the cord. Although, when a sterile environment can be provided, standard practice is to sever the cord with a cutting instrument after tying it off, instead of leaving the cord and placenta attached until they disconnect naturally, which can take several days. --47.146.63.87 (talk) 06:45, 22 February 2019 (UTC)