The
Golden Book of Chemistry Experiments (1960)
by Robert Brent. Illustrated by Harry Lazarus.
[ pdf |
Scribd ]
This excellent children's book was banned from public libraries because some of the experiments were
(over-protectively) judged too dangerous for the intended audience.
Anne-Marie Helmenstine, Ph.D. has posted several comments:
2007 |
2008 |
2010 |
(2011-07-31) Chemistry Set from a Bygone Era (c. 1964)
The contents of the chemistry set I had as a child (if memory serves).
A chemistry set should be fun but it should also serve as
an initiation to safety procedures.
Here is the list of the basic equipment in the chemistry set which
I learned to use safely as a child.
Two wooden racks were provided with small quantities of inorganic and
organic chemicals in labeled glass tubes with plastic stoppers.
Some of those tubes were empty, probably because their intended content was deemed
too dangerous (lye) or too expansive (silver nitrate).
The silver nitrate container was darkened.
(2011-07-12) PTFE = polytetrafluoroethylene (Teflon® )
(CF2 )n was discovered accidentally by
Roy J. Plunkett in 1938.
On April 6, 1938, Plunkett and his assistant, Jack Rebok, found that a
steel cylinder in which they had stored
tetrafluoroethylene (TFE)
contained a waxy powder instead (they had to cut the cylinder open).
The compressed gas had spontaneously polymerized into PTFE.
(2011-07-12) Joints
Ground-glass joints, hose connections, etc.
Ground-glass conical joints
In the trade, the inner contact surface is known as the grind.
All standard joints have a precise 1:10 taper. Their sizes are specified by
two numbers; the largest diameter of the grind (in mm)
and the length of the grind (in mm).
A mismatch in length is usually inconsequential.
A slight diameter discrepancy can also be tolerated.
The 10/30 long joint seems to be for thermometers only...
Sizes (diameter/length in mm) of Ground-Glass Conical Joints
Keck Clip
Size
Wall Thickness
US (long)
DIN 12249
Other (short)
3.5-5.0 mm
100/60
3.5 mm
85/55
3.2 mm
71/51
2.5-3.2 mm
60/46
2.5-3.2 mm
55/50
55/44
2.3-2.5 mm
50/50
50/42
brown
2.3-2.5 mm
45/50
45/40
gold
6
2.0-2.3 mm
40/38
orange
5
2.0-2.3 mm
34/45
34/35
34/28
red
4
2.0 mm
29/42
29/32
29/26
green
3
1.8-2.0 mm
24/40
24/29
24/25
blue
2
1.8 mm
19/38
19/26
19/22
yellow
1
1.5-1.8 mm
14/35, 14/20
14/23
14/19
violet
1.5-1.8 mm
12/32
12/21
turquoise
0
thermometer
10/30
1.5 mm
10/30
10/19
1.5 mm
7/25
7/16
0.8 mm
5/20
5/13
Keck clips were patented in 1984 (US patent
4,442,572) by Hermann Keck.
They are available mostly for medium-sized glassware joints (10 mm to 45 mm
in diameter) in the above Delrin® color coding.
(2011-07-11) Titration (volumetric analysis)
Measuring volumes and concentrations.
Titration is an elementary method of analytical chemistry
which consist in measuring what volume a known titrant
(or titrator) solution should be added to an unknown solution
for an observable reaction to occur.
Often, what makes the reaction observable is the addition to the unknown solution
of a minute quantity of a color indicator which changes
color under precise conditions.
Three type of titrations are based on color changes brought about, respectively,
by a change in acidity, oxydizing potential or the concentration of
complexified metal cations.
A related fourth type of titration is based on the observation of the precipitation
of a sparingly soluble specific solute.
1. Acid-base titration :
This is the most common form of titration;
it serves as an introduction to the subject at the high-school level.
Student are introduced to pH indicators
and trained in the basic titration techniques, using a
burette.
2. Redox titration :
A spectacular introduction is the blue bottle demonstration.
3. Complexometric titration :
A complexometric
indicator (also known as a "pM indicator", where "M" stands for "metal")
changes color as it forms a weak complex with a specific metallic cation.
(2015-07-18) Acid-base indicators
(pH color indicators).
Solutes whose colors depend on the acidity of the solution.
An acid-base color indicator is a substance which undergoes a reversible
color change with varying pH.
Substances that undergo an irreversible color-changing degradation
above or below a certain pH can be used to spot-check an existing
acidity level, but they are not proper indicators.
Most commonly,
a pH color indicator is a
weak acid HA (of dissociation constant
Ka)
which differs in color from its conjugate base
A- .
[ H+ ] [ A- ]
/ [ HA ] = Ka
Somewhere in the color transition range (exactly where depends on
the optical characteristics of the two colored species)
there's a point where the two conjugate concentrations are equal.
At that point, we have:
pH = pKa
Some weak acids undergo multiple color changes at different
pKa values.
Color transitions of some pH indicators.
Roman numerals indicate multiplicity.
Data compiled from multiple sources. Precision and/or reliability may vary greatly.
The highlighted names (first column) are the indicators routinely used by the author.
Before the invention of digital pH-meters,
there were many more color indicators to choose from.
Eastman-Kodak alone was once offering up to 67 different indicators
(Ellen McCrady, 1995).
Litmus :
The oldest indicator of acidity still in use is
Litmus,
which was discovered around 1300 by the Catalan physician
Arnau de Vilanova (c.1240-1311).
Traditional litmus (CAS 1393-92-6)
is a mixture of about a dozen substances extracted from
Roccella tinctoria
(Orchilla weed, described by Pyrame de Candolle in 1805)
or, more recently,
other lichens
(which are also the source of Orcein).
Such dyes have been known generically, since ancient times,
as lichen purple.
Litmus was first analyzed in 1840 by the Irish chemist Sir
Robert Kane (1809-1890).
The main constituents of commercial litmus are:
Red-cabbage juice :
The active ingredients are anthocyanins
which are the pigments that make red-cabbage purple, poppies red and cornflowers blue.
Arguably, this is the most readily available pH indicator.
Its multiple active components induce several color transitions.
Red-beet juice :
There are no anthocyanins in red beets.
The single
active dye is
betanin (E162, Beetroot red)
at a concentration of about 500 mg/kg (0.05%).
It changes from red to yellow between pH 11 and pH 12.
Turmeric :
The active dye is curcumin
(E100, Turmeric yellow) which is also a redox indicator.
It gives its yellow color to
curry (curry contains turmeric).
Curcumin is yellow below pH 7.4 and red above pH 8.6.
Red carmine :
Carminic acid
(C22H20O13 )
is the active constituent (12%) in cochineal powder,
obtained by grinding the bodies of dried female cochineal insects
(Dactylopius coccus)
mixed with aluminium or calcium salts.
It takes about 70000 insects to obtain a pound of
cochineal powder, containing about 50 grams of carminic acid.
This was a substantial trade in Mexico during Spanish colonial times.
Renewed interest in natural dyes has made the product profitable again
for cosmetics (Peru is now the leading exporter).
Carminic acid (CAS 1260-17-9) has a pKa of 3.13
(2010).
Yellow in acid, it has a deep violet color in an alkaline solution.
Universal Indicators :
Universal indicators are just mixtures of
several simple indicators from the above list,
carefully chosen to produce different colors
in successive ranges covering a large part of the pH spectrum.
The most popular universal indicators give the illusion of taking
on a color varying continuously from red (very acidic)
to violet (very alkaline) like the
colors of the rainbow.
(2015-08-13) Methylene blue
The classic blue bottle demonstration.
More recently, another more colorful version of the same demonstration has become
popular. By using indigo carmine
instead of methylene blue the different stages are
indicated by three different colors (red, yellow, green).
Ferroxyl indicator is an aqueous solution containing
red prussiate (potassium ferricyanate), with
phenolphthalein and sodium chloride.
It turns blue in the presence of ferrous ions (Fe++)
due to the formation of
Prussian blue.
(2015-08-15) Sugar Snake
Dehydration of sugar produces a steaming column of foamy carbon.
Sugars are called carbohydrates because they
can decompose into carbon, water and nothing else.
(Experiment with sucrose, glucose, fructose, etc.)
A very strong dessicant like concentrated sulfuric acid is able to break down
sugar molecules to extract the water and leave only pure carbon behind.
The reaction combines sugar dehydration and dilution of water in sulfuric acid,
which are both strongly exothermic. Some of the heat produced converts water to steam.
(2011-08-28) Negative-X A mixture that's ignited by water.
The main reaction is:
NH4NO3 + Zn
®
N2 + ZnO + 2 H2O
However, it is best ignited by the following reaction,
catalyzed by Cl- ions:
NH4NO3
®
N2O + 2 H2O
That subsidiary reaction can be started with a drop of concentrated hydrochloric acid.
Alternately, pure water (or just moisture) will ignite a mixture that
already contains a little bit of chlorine ions, in the form of
ammonium chloride (or sodium chloride).
Also, the acidity may remove the oxidation layer
of zinc to make the metal available for the main event.
(2011-07-10) Basic Glassware
