(2011-07-31) 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 asan initiation to safety procedures. Here is the list of the basic equipment in the chemistry set whichI learned to use safely as a child.
Two wooden racks were provided with small quantities of inorganic andorganic chemicals in labeled glass tubes with plastic stoppers. Some of those tubes were empty, probably because their intended content was deemedtoo dangerous (lye) or too expansive (silver nitrate). The silver nitrate container was darkened.
(2011-07-12) (Teflon®) (CF2)n was discovered accidentally by Roy J. Plunkett in 1938.
On April 6, 1938, Plunkett and his assistant, Jack Rebok, found that asteel cylinder in which they had storedtetrafluoroethylene (TFE) contained a waxy powder instead (they had to cut the cylinder open). The compressed gas had spontaneously polymerized into PTFE.
(2011-07-12) 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 bytwo 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 patent4,442,572) by Hermann Keck. They are available mostly for medium-sized glassware joints (10 mm to 45 mmin diameter) in the above Delrin® color coding.
(2011-07-11) Measuring volumes and concentrations.
Titration is an elementary method of analytical chemistrywhich consist in measuring what volume a known titrant (or titrator) solution should be added to an unknown solutionfor an observable reaction to occur. Often, what makes the reaction observable is the addition to the unknown solutionof a minute quantity of a color indicator which changescolor 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 ofcomplexified metal cations. A related fourth type of titration is based on the observation of the precipitationof 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 topH indicatorsand trained in the basic titration techniques, using aburette.
2. Redox titration :
A spectacular introduction is the blue bottle demonstration.
3. Complexometric titration :
A complexometricindicator (also known as a "pM indicator", where "M" stands for "metal") changes color as it forms a weak complex with a specific metallic cation.
4. Precipitation titration :
(2015-07-18) 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 degradationabove or below a certain pH can be used to spot-check an existingacidity 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 onthe 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.
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, sinceancient times,as lichen purple.
Litmus was first analyzed in 1840 by the Irish chemist SirRobert 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. Thesingleactive 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 tocurry (curry contains turmeric). Curcumin is yellow below pH 7.4 and red above pH 8.6.
Red carmine : Carminic acid () 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 againfor 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 ofseveral 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 takingon a color varying continuously from red (very acidic) to violet (very alkaline) like thecolors of the rainbow.
Yamada's Universal Indicator (1933).
Bogen's Universal Indicator.
(2015-08-13) The classic blue bottle demonstration.
More recently, another more colorful version of the same demonstration has becomepopular. By using indigo carmine instead of methylene blue the different stages areindicated by three different colors (red, yellow, green).
(2015-09-18)
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) Dehydration of sugar produces a steaming column of foamy carbon.
Sugars are calledcarbohydrates because theycan 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 downsugar 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.
(2011-08-27) 1 g of sodium polyacrylate can hold 825 mL of water.
(2011-08-28) 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 thatalready contains a little bit of chlorine ions, in the form ofammonium chloride (or sodium chloride). Also, the acidity may remove the oxidation layerof zinc to make the metal available for the main event.
(2011-09-06) An explosive set off by the touch of a feather or by alpha radiation.
(2011-07-10) 
