Short questions on science and technology.

98 responses total.

Does anyone know why iron turns red when oxidized (rusted) and green when
reduced, while copper turns green when oxidized (as in copper roofs) but red
when reduced (as in Chinese pottery glazes)?
        Why does old lime (presumably CaO-H2) not remove the skins from dried
soaked corn as well as new lime (unhydrated)?  Would gypsum (Ca2SO4) work?
Epsom salts (Mg2SO4- used to make tofu by coagulating the proteins)?
        What is the fuel use (kerosene) per person per mile for air travel,
with the average occupancy?  Gallons/person/mile.

If exposed to air, my guess is that old lime contains a fair amount of
CaCO3 - which is far less reactive than CaO or Ca(OH)2.

Don't you mean CaSO4 and MgSO4?  I don't think that either would work.

Re #1:  I believe I have seen a figure in the neighborhood of 50
passenger-miles per gallon for a 747, but I could easily be way off.

Ferric (oxidized) oxides are generally red and ferrous (reduced)  oxides
are generally black. Ferric salts are usually yellowish and ferrous salts
are blue/green. Colors in compounds correspond to electronic transition
energy levels and are the subject of quantum chemistry.

Copper compounds are all blue or green but metallic copper, which
is formed when the compounds are reduced, is red. 

Lime (CaO) reacts with water to form "hydrated lime" - calcium hydroxide
-. This then reacts with CO2 in the atmosphere to make calcium carbonate
via Ca(OH)2 + CO2 = CaCO3 + H2O. 

It is the alkalinity of Ca(OH)2 that is the active property. Lye will
do the same thing. CaCO3 is not soluble.

Thanks, Rane.  I am now soaking my mostly-limestone in water and plan to
decant off the soluble part and use that as my alkali.  I will use a large
excess and hope that works.  Don't want to fool with lye.  Will washing soda
work about as well?
        Now I know why Coca Cola bottles are green.  Is the brown found on
half-oxidized copper roofs a combination of copper-red and copper-green?

Someone was claiming that flying uses less fuel per passenger than driving.
This might be true for Americans, who drive 20 mpg cars with no passengers.
A full car uses less fuel per passenger than whatever plane they got that
figure from.  A train would probably be a vast improvement over both,
especially as there is less wheel friction and less drag.

        Salts of iron with what?

Washing soda is not as alkaline as a hydrated lime solution, but nearly so.
You could try it. 

Old bottles are greenish because of iron. Removing the last trace, to make
clear bottles, is difficult.

Copper turns brown first because of oxidation - the oxide is black. With
time this converts to the green basic carbonate.

Iron salts such as chlorides, sulfates, nitrates, etc. These are all
soluble.

The decanted water from the limestone is pH at least 11 (it is a dark blue,
and pH 11 is a greenish blue).  I will compare this with a concentrated
solution of washing soda.  Are you sure the alkalinity is the essential part,
not the Ca or K found in lime or wood ash (used for hominy grits by my
neighbor in her childhood)?  Joy of Cooking suggested baking soda for hominy
grits, may check the pH on that, too.

Does oxidized iron also eventually convert to carbonate?

Have not yet tried to remove the skins after boiling my soaked corn for 1.5
hours at pH > 11.  But it still looks red, and when boiled with fresh lime
it would turn and stay green.  But that was a different corn variety.  What
in corn turns colors?

I have been making salt-pickled vegetables.  Why does sauerkraut and also
pickled daikon turn pink when pickled with salt?  They are closer to white
to start with.
Red cabbage has turned the water beet-colored, anthocyanins?

The corn skins came off without even rubbing, pH 11 it will be!  Thanks, the
tortillas were excellent and I am about to boil more corn.

I did some searching today.  I found some specs on a very
old model of 747 (the 747SP, first flown in 1976):

Fuel capacity:  49,231 gallons
Flight range:  6800 miles (current models can go 8600 miles).
Number of passengers:  244 (current models go over 400).

Assuming that a full load of passengers can be carried
for a maximum-length flight (probably doable, by carrying
less cargo), the flight would achieve 1,659,200
passenger-miles.  If all the fuel was burned on the
trip, this would amount to 33.7 passenger-miles per
gallon.  (In practice, a reserve is always carried and
is never burned except in emergencies.  No range spec
would assume use of the reserve.)

Current models of the aircraft have more efficient engines
and lower-drag airframes.  I'll wager they are beating
45 passenger-miles/gallon by now.

That assumes the plane is flying full of passengers.  What is the typical
percentage of empty seats?  Jim points out that there are more ground miles
than air miles between here and California because of hills and obstacles.
How do air-miles compare wtih highway miles?  How many miles to drive to NYC
versus to fly?  Anyone know the figure for full trains?  Long ones.

The extract from red cabbage is an indicator. Try making a solution of
it alkaline. I don't know the pH at which it changes, however. 

It turns from reddish-purple to blue, like other fruit-based stains in
clothing that you are trying to remove with soap.  Do you know the chemistry
of this?  I found 'delphinium blue', which consists of three six-carbon rings,
two sharing a side and one other linked at its corner, and the middle ring
also has an oxygen instead of a carbon, plus six estra O's.
'Many of the colors vary with acidity.  One group is red in acidic solutions,
mauve in neutral media and blue in alkalis....They are present in cornflowers,
in which the pink variety has more acidic sap than the common blue forms....
in some types of forget-me-not the acidity of the flower increases with age.
Another group of flavonoids is colorless in acidic media but turns yellow when
alkaline.'  (I got chamomile tea to turn colorless by adding baking soda).
Red-blue ones are called anthocyanins and colorless-yellow ones anthoxanthins.
Some plants have both classes.  'The juice of pickled red cabbage, for
example, is red only if it is acidic;  but if ammonia or washing soda is
added, the acid is neutralized, and so the anthocyanins turns blue and the
anthoxanthins turn yellow;  thus the juice changes through variou s shades
of purple, blue and turquoise to green.'  Quite a party trick!
        Maybe I can use the pickled red cabbage as an indicator when making
tortillas - if it turns green, the alkalinity is high enough.
        The red-orange colors in plants are usually from carotenoids, but the
reds of autumn leaves are from flavonoids (red-blue or yellow group), which
form best under cool conditions in bright sunlight.  So cold clear autumn days
produce the best leaf colors.
        Carotenoids color carrots, tomatoes, corn and marigolds.  Their
backbone is a long carbon chain with a six-carbon ring at each end.
(Hazel Rossoti, Colour  Why the World Isn't Grey)

Re #11:  The 747 was designed to be a freight carrier, so any figure
you see is going to include a lot of freight mass as well as bodies
(except maybe for the 500-passenger Japanese commuter planes).

I don't know the chemical names or color numbers of the indicators in
cabbage or delphiniums so haven't been able to look them up (my sources do
not give information based on 'cabbage' or 'delphinium'). However all
indicators are dyes that contain several reactive groups that make them
acidic or basic, such as R-COOH, R-SO3H, or R-OH (on a benzene ring),
which are acidic, and R-NH2 or R=NH, and some others, which are basic. (R-
is the general symbol for the rest of an organic molecule. The rest of the
molecule has alternating single and multiple bonds, which allow electrons
to slosh back and forth. The colors are a consequence of the frequencies
at which the electrons "resonate" on the structure, and the colors are
changed by whether a group is, say, R-COOH or its ionized form R-COO-, or,
say, R-NH2 or its ionized form, R-NH3+. ; 

Of course, there are a lot of dyes that are not indicators, such as the
flavenoids and carotenoids that you mention. These lack the acidic/basic
groups, but have the alternating single and multiple bond structures.

        Airplanes don't travel airport to airport by straightest line.
Take off and landing patterns add miles, as do air routes, such that 
a Detroit - New York flight might fly over or near Lake Erie and up
the St. Lawernce waterway, until it can turn right and head direct
east to NYC.
        However airport to airport distances are computed as curved
string lines arcross our Globe.

Yes, Detroit planes usually take off to the southwest before turning northwest
to fly over Ann Arbor.  Jim gueses actual distances might be 20% longer, but
the factor probably depends on total distance.

What makes purple green beans turn green when cooked?  Is the dye degraded?

Jim concludes that 2 people travelling in a car (with freight) is more fuel
efficient than 2 people in a plane.

Jim has a new question relating to electronics.  He has a TTL amber monitor.
When there are only a few characters on the screen they are all very dim. 
The more characters he puts on the screen, the brighter it gets.  He says no,
it is not a TTL but a monochrome VGA, is this typical of mono VGAs?  At a
certain point he gets full screen signal and guesses that the monitor is set
up on the assumptin that there will be a lot of background signal at all
times.  He has not noticed this with a paper white VGA.  A friend offered us
a similar amber VGA to compare.  When he does clear screen it quickly fades
to very dark as soon as the number of characters goes to very small.
Is this a defective monitor or a design flaw or maybe the software and/or
controller card?
        (Rane, thanks for the explanation of acidic and basic groups accepting
or losing hydrogen ions).

I got a book on dye plants (written by botanists) and they mention that
tannins (brown) are formed from other dye molecules and are found mainly inteh
bark and near wounds and in galls.  I was wondering what function dye
molecules perform for plants, other than in flowers and fruits, and it looks
like they may react with invasive organisms (those extra electrons could mess
up the metabolism of some monocellular creature, just like they messed up my
skin when I husked black walnuts).  I have also read that saffron protected
cloth from insects, and indigo prevented mildew.  Jim got a different VGA
monitor (not saffron colored but white):  'nothing happened' (he forgot to
plug it into a power source).  No problem seeing just a few characters on this
one, no dimming effect.  Maybe the other monitor is going bad.

Chemicals have colors because of the way their electrons interact with
light. It can be that some colors are totally incidental to the function
that chemical serves in the plant. Actually, ALL chemicals are colored, but
not all in the spectrum range that humans can see. 

That said, many colored chemicals (dyes) in plants evolved to serve
functions.  Chlorophyll helps collect light energy. Flower colors evolved
(were selecte4)  to attract insects (not many families of animals have
color vision, but insects and birds do, though not always in the human
spectrum range). All the chemicals that evolved for defense (by being
poisonous, or unpalatable, etc) may or may not be colored, incidentally to
their function. The color functionality has no necessary relation with
toxicity or palatability, although selection has led to some insects to
use mimic colors so they look like an unpalatable species when in fact
they themselves are not. 

I could not think of any functional reason for roots or sap to be colored.
Today I mixed up some more old lime, checked with pH paper that it was at
least pH 11 (bright blue), and then put a piece of pickled red cabbage into
it.  The cabbage quickly turned purple then blue and then exuded an emerald
green.  The cabbage itself remained purply-blue.  My book shows the transition
from red purple blue turquoise (missed that) to green, with green at the high
end of the pH.  When my pH paper runs out, all I have to do is buy a red
cabbage (hopefully it will also work without prior fermentation to the red
range of acidity).  The cabbage has been going about two weeks and tastes as
sour as pure vinegar so I refrigerated it.  I can use just the juice for pH.
The corn itself (to which I add the lime water) also turns from an orangy to
a dark green color, presumably the red turns to blue and the yellow gets
stronger or at least persists.  The kernels are bright yellow, no green. 
There is also yellow, red, or blue corn, but apparently corn is not naturally
alkaline, so no emerald-green corn.
        Many vegetables come in either purple or green versions, perhaps this
is due to variations in alkalinity (at higher pH the purple goes to green):
green beans, peppers, brussels sprouts, cabbage, lettuce, chard/beets, turnip,
red versus white runner bean seeds, onions, garlic, eggplant (white or purple,
no yellow pigment?), purple carrots were the original color, gooseberry, red
or yellow cherries (missing pigment here?), red or white currant.  Pink or
white grapefruit.

Both our red LED clocks get 10-20 minutes ahead between resettings (time
changes or power outs).  Why?  Is the local Ann Arbor current 'fast'?  The
dial clocks are okay (60 cycles).  How do LED clocks operate?

Usually they operate by counting cycles on the input line.
However, I have found that spurious signals such as high levels
of RF can cause them to count fast.  You may have a similar problem.
I don't know of a cure.  Battery-powered quartz clocks are cheap
and don't have this issue, so if you don't need to read them in
the dark, you might want to get a couple.

The speedup is not a problem, just a curiosity.  Thanks for the info.

I discovered while making tortillas that if you are too busy to finish making
them after you soak in CaCO3, boil for an hour, and then rinse 25 times, and
you leave them overnight soaking in the refrigerator in clean water, you no
longer have the caustic effect when you eat them.  There must be alkali
trapped inside after boiling that gets released slowly.  But the steam from
boiling the corn is hard on the nose.

Here's a math question for somebody. In my Algebra 2 textbook the sine and
cosine functions are defined in terms of the coordinates of the point where
the terminal side of an angle intersects the unit circle. Then they go on
to find the sine and cosine for some special angles- pi/2, pi/4, pi/3, pi/6. 
How do you find the values of these functions for an arbitrary angle, in the
absence of a calculator (or a slide rule)? I saw the series that Rane posted
in a response in agora, but it would be nice if someone could explain why it
works.

It works because that (and similar ones for cosine, etc) are the Taylor
series expansions of the function. There are such series for *all*
functions, and they are derivable by a relatively simple operation (if you
know calculus). Mathematicians have worked for hundreds of years on
deriving alternative way to express one function in terms of others. In
this case, it is the harmonic function being expressed as polynomials.
[The real answer to why it *works* is because they give the same value.
Less pedantically....an expression like sine(x) is just a shorthand for
some operations that give the ratio of the opposite side to the hypotenuse
for the an acute angle of a right triangle - the series is one such
arithmetic operation.] 

Ah well, I suppose I will have to wait until calc class next year in order
to properly understand it...thanks anyway.

Yup.

(Levity:  Did you hear about the mathematician who took dirty dancing
lessons?  He got a lambada calculus.)

In biology class the other day a couple of friends and I got to talking about
dissolving salt in water. Of course it forms Na+ and Cl- ions. Chlorine is
poisonous and sodium ignites in contact with water, but neither
of these reactions happens. Why? My guess was that since the ions have 
the same electron configurations as noble gases, they are nonreactive. Is
this right?

On a related note: Acids attack things because an H+ has no electrons and
therefore can get closer to the outer electrons of other atoms and "pull"
them away. (At least, this is what I was told in an introduction to chem
class last year.) Why are bases, with [OH]- ions, caustic?

Sodium metal reacts by giving up an electron. Once it does that, it
has the "inert gas" configuration of 8 electrons in the outer shell,
and is rather unreactive (although charged, which is its main chemical
property). Same for chlorine. It reacts by accepting an electron to
complete its outer shell with 8 electronics. It is then also relatively
unreactive. So, your right that they have the same configurations
as noble gases. 

Acids only attack things from which it can accept electrons. It may
not *take* the electronc (which would yield a hydrogen atom, which
would produce hydrogen gas, H2); it may instead simply borrow an
electronic to form a covalent bond. So, again, your are right about
acids. Bases are "caustic" because they grab protons to produce water,
and hence cause reactions that occur upon removal of a proton (H+). 

We did an "experiment" in chemistry a few weeks ago in which we filed pennies
to expose the Zn inside, then put them in HCl solution overnight. If I
remember correctly, it produced H2 gas and ZnCl (or perhaps it is ZnCl2
<oddie does not have a periodic table with him at the moment>), though the
copper did not appear to react at all. This would seem to be a  case of the
H+ ion actually stripping an electron off another atom, forming Zn+ ions
that then were attracted to the Cl- in solution. (I believe ZnCl is ionic
because it consists of a metallic and a non-metallic ion, but I could
be wrong.) In this year's chem class we are only now getting to formation
of molecular bonds; we spent much of the first quarter doing "introduction
to quantum theory." Our teacher offered us some extra credit if we could
solve the Schrodinger wave equation for neon over the weekend ;-P

ZnCl2. It is ionized in solution. Whether a metal reacts with acid to
produce hydrogen depends upon its position with respect to hydrogen in the
"electromotive servies". Zn is "above" H2; Copper is below. You can force
copper to react, though, by changing the conditions.  (Sorry for all the
typos in #32: an effect of sleep deprivation.) 

The way I heard it, you don't get H+ ions. Instead you end up with H3O+ ions,
with that loose proton attaching itself to a water molecule.

That is true to various degrees to all ions in solution, since the ions
are charged, and water is polar. 

You're right Andrew.  I reread the chapter in the chem textbook on acids and
bases last night. Wouldn't the third bond on H30+ be weaker than the original
bonds forming H2), though? What is the charge difference between the ends
of a water molecule?

I have been trying to figure out the chemical formula of isopropyl alcohol,
the stuff sometimes sold as "rubbing alcohol." An alcohol has a formula
of the form R-0H, says the textbook, and propane is a 3-carbon hydrocarbon
so my guess is this:

 | | |
-C-C-C-OH
 | | |

What does "iso" (Latin for "the same," is all I know) mean in this context?
Could you have an alcohol based on an alkene, alkyne or even a benzene
ring, rather than an alkane?

Isopropyl has the -OH on the middle carbon, I believe.

Asked my chem teacher about isopropyl alcohol today. He says that the "iso"
is sort of a leftover from an older system of naming, and indicates that
the molecule is symmetrical. It does indeed have the hydroxyl on the middle
carbon, so its proper name is 2-propanol.

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