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Hands-on Chemistry

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Making TCPO for a Glow Stick (revisited)  |  Test-Tube Thunderstorm
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 International Year 
 of Chemistry - 2011

Hands-on Chemistry
 Beaker  Beaker

(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.

  • Glass stirring rod.
  • Round-bottom and flat-bottom boiling flasks.
  • Verres à pied  (no beakers).
  • One-hole and two-hole stoppers.
  • Thistle funnels and glass tubes.
  • Retort
  • Mortar and pestle.
  • Evaporating dishes.
  • Crucible.
  • Tripod and wire gauze  (with asbestos center).
  • Alcohol burner with wick.
  • Test tubes and wooden rack.
  • Wooden test-tube clamp.
  • Test-tube cleaning brush.
  • Plastic crystallizers  (one with built-in electrodes).
  • Earthenware gizmo  (pierced bowl with sideways indentation).
  • Litmus paper  (French:  papier de tournesol ).

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.

  • Iron filings.   Fe   55.845 g/mol.
  • Sulfur.   S   32.065 g/mol.
  • Zinc dust.   Zn   65.379 g/mol.
  • Pyrolusite = Manganese dioxide.   MnO2   86.937 g/mol.
  • Condy's crystals = Potassium permanganate.   KMnO4
  • Sodium bisulfite.   NaHSO3
  • Copper sulfate.   { CuSO4 , 5H2O }   249.685 g/mol.
  • Lunar caustic = Silver nitrate   { AgNO }   169.873 g/mol.
  • Baking soda = Sodium bicarbonate.   NaHCO3
  • Washing soda = Sodium carbonate.   Na2CO3
  • Caustic potash.   KOH   56.106 g/mol.
  • Lye = caustic soda = sodium hydroxide.   NaOH   39.997 g/mol.
  • Glucose.   H(CHOH)5HCO   180.156 g/mol.
  • Oxalic acid.   { (COOH)2 , 2HO }   126.066 g/mol.
  • Citric acid.   { (CHCOOH)COH COOH , HO }   210.139 g/mol.
  • Tartaric acid.   { (CHOH COOH)2 }   150.087 g/mol.
  • Malic acid.   { COOH CH2 CHOH COOH }   134.087 g/mol.

A few other common compounds may provide a slightly richer playfield:

  • Table salt = sodium chloride.   NaCl   58.442 g/mol.
  • Epsom salt = magnesium sulfate.  { MgSO4 , 7H2O }  246.475 g/mol.
  • Table sugar = sucrose = saccharose.   C12H22O11   342.297 g/mol.
  • Fruit sugar = fructose.   C6H12O6   180.156 g/mol.
  • Galactose.   C6H12O6   180.156 g/mol  (vs. glucose & fructose).

 Aspirator bottle (2011-07-10)   Basic Glassware
Handling liquids  (and gases).

  • Test tube.  Boiling tube  [ tube à essai ].
  • Stirring rod  [ agitateur ].
  • Crystallizer, crystallizing dish  [ cristallisoir ].
  • Petri dish  [ Boîte de Petri ].
  • Watch glass  [ Verre de montre ].
  • Measuring cylinder  [ éprouvette graduée ].
  • Volumetric flask  [ fiole jaugée ].
  • Buret  [ burette ].
  • Pipet  [ pipette ].
  • Thistle funnel, thistle tube.
  • Separatory funnel  [ ampoule à décanter ].
  • Dropping funnel  [ ampoule de coulée ].
  • Pressure-equalizing dropping funnel  [ ampoule à brome ].
  • Eudiometer  (Landriani, 1775).
  • Aspirator bottle  (bottom side-arm).
  • Bottle  [ flacon ].
  • Squeeze bottle  [ pissette ].
  • Round-bottom flask, Boiling flask, Florence flask  [ ballon ].
  • Flat-bottom flask.
  • Beaker  [ bécher ].
  • Conical flask  (Emil Erlenmeyer, 1861).
  • Filter flask, side-arm vacuum flask, Büchner flask, Kitasato flask.
  • Büchner funnel  (with either filter paper or sintered/fritted glass).
  • Büchner ring.
  • Desiccator jar.
  • Water aspirator  [ trompe à eau ].
  • Retort [ Cornue ]  (Geber, c. AD 750).
  • Alembic, still  [ alambique ].
  • Liebig (straight) and Graham (coiled) condensers  [ réfrigérants ].
  • Kjeldahl bulb  (or "ball").
  • Bump trap  (reflux trap).
  • Rotary evaporator  (or "rotovap").   [ video | MIT | use ]

Wikipedia :   Laboratory glassware   |   Laboratory glassware
French :   Verrerie de chimie   |   Matériel de chimie  (Quizz about names of glassware in French)

(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.

PTFE  has a very low  friction coefficient  and is virtually inert chemically.

 Come back later, we're
 still working on this one...

(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
 Size  Wall
   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 mm55/50 55/44
   2.3-2.5 mm50/50 50/42
brown  2.3-2.5 mm45/5045/40 
gold6 2.0-2.3 mm  40/38
orange5 2.0-2.3 mm34/4534/3534/28
red4 2.0 mm29/4229/3229/26
green3 1.8-2.0 mm24/4024/2924/25
blue2 1.8 mm19/3819/2619/22
yellow1 1.5-1.8 mm14/35, 14/2014/2314/19
violet  1.5-1.8 mm12/3212/21 
  turquoise   0   thermometer  10/30  
1.5 mm10/3010/19 
   1.5 mm7/257/16 
   0.8 mm5/205/13 

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.

 Come back later, we're
 still working on this one...

Wikipedia :   Ground glass joint   |   Sciencemadness Forum
Scribd's e-book :   Interchangeable Ground-glass Joints, Stopcocks
Trade :   Eagle Laboratory Glass Company   |   Glasscraft   |   Witeg   |   Duran Group

 Bottom of the meniscus in a buret
(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 :

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.

4.   Precipitation titration :

 Come back later, we're
 still working on this one...

Titrimetric methods  by  Marcin Borkowski.       Wikipedia :   Titration   |   Acid-base titration

(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  indicatorsRoman numerals indicate multiplicity.
Thymolphthalein (I) C28H30O4 Red0.0Colorless
Phenolphthalein (I) C20H14O4 Orange0.0Colorless
Picric acid (TNP) OHC6H2(NO2)3 Colorless0.20.381.0Yellow
Cresol red (I) C21H17NaO5S Red0.21.01.8Yellow
Crystal violet 10B C25H30N3Cl Yellow-
Phenol red (I) C19H14O5S Red1.2Yellow
Malachite green (I) C23H25N2Cl Yellow0.21.301.8Green
Thymol blue (I) C27H30O5S Red1.21.652.8Yellow
Methyl green C27H35N3BrCl ZnCl2 Yellow2.03.0Blue
Quinaldine red C21H23N2I Colorless1.32.633.2Red
Methyl violet 2B C23H26N3Cl Yellow0.152.1?3.2Violet
Methyl yellow C14H15N3 Red2.93.34.0Yellow
Methyl orange C14H14N3SO3Na Red3.13.464.4Yellow
Bromophenol blue C19H10Br4O5S Yellow3.03.854.6 Blue
Congo red C32H22N6(SO3Na)2 Blue3.04.15.2Red
Helianthine (??) C8H10N3SO3Na Orange3.45.0Pink
Bromocresol green C21H14Br4O5S Yellow3.84.85.4Blue
Resazurin C12H7NO4 Orange3.86.5Violet
Methyl red C15H15N3O2 Red4.44.956.3Yellow
Propyl red C19H23N3O2 Red4.85.486.6Yellow
Azolitmin (Litmus) C10H11N3O Red4.58.3Blue
Chlorophenol red C19H12Cl2O5S Yellow5.06.256.7Red
Bromocresol purple C21H16Br2O5S Yellow5.26.356.8Purple
p-Nitrophenol OHC6H4NO2 Colorless5.47.157.6Yellow
Neutral red C15H17N4Cl Red6.87.28.0Amber
Bromothymol blue C27H28Br2O5S Yellow6.07.307.6 Blue
Phenol red (II) C19H14O5S Yellow6.87.78.2Fuchsia
Curcumin (Turmeric) C21H20O6 Yellow7.47.88.6Red
m-Nitrophenol OHC6H4NO2 Colorless6.88.288.6Yellow
Cresol red (II) C21H17NaO5S Yellow7.18.468.8Purple
Thymol blue (II) C27H30O5S Yellow8.09.209.6Blue
o-Cresolphthalein C22H18O4 Colorless8.29.619.8Violet
Phenolphthalein (II) C20H14O4 Colorless8.39.710.0Fuchsia
Thymolphthalein (II) C28H30O4 Colorless9.310.110.5Blue
Alizarin yellow R C13H8N3NaO5 Yellow10.111.012.0Red
Trinitrotoluene (TNT) CH3C6H2(NO2)3 Colorless11.213.0Orange
Indigo carmine C16H8N2O8S2Na2 Blue11.412.213.0Yellow
Phenolphthalein (III) C20H14O4 Fuchsia12.013.0Colorless
Malachite green (II) C23H25N2Cl Green11.613.2Colorless
Titan yellow C28H19N5O6S4Na2 Yellow12.213.2Red
1,3,5-Trinitrobenzene C6H3(NO2)3 Colorless12.014.0Orange
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).

 Augustin Pyrame de Candolle (1778-1841) 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:

Contributions to the Chemical History of Archil and of Litmus  by  Robert Kane.  Philosophical Transactions of the RS130 (1840), pp. 273-324.
Mémoire pour servir à l'histoire chimique de l'orseille et du tournesol
by  Robert Kane.  Annales de chimie et de physique,  ser. 3, vol. 2  (1841).

Natural Indicators :

Besides  litmus,  several plant extracts are noteworthy for historical reasons:

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.

  • Yamada's Universal Indicator (1933).
  • Bogen's Universal Indicator.

pH scale (1909)   |   pH calculator   |   Acid-base indicators  by Fred Senese.   |   RSC: Indicators.
Determination of the pKa of Phenolphthalein  by  Manuel Alonso  et al.  (September 2010).
pKa of Drugs and Reference Compounds   |   Dissociation constants of organic acids and bases
The colors and chemistry of pH indicators  by  Andy Brunning   (Compound Interest, 2014-04-04).
pH-meter   |   Chempendix     Wikipedia :   pH indicator   |   Universal pH indicator
Video :   Chemical Curiosities:  Surprising Science and Dramatic Demonstrations  by  Chris Bishop.

(2015-08-13)   Methylene blue
The classic  blue bottle  demonstration.

 Come back later, we're
 still working on this one...

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).

Wikipedia :   Methylene blue   |   Blue bottle
Videos :   Blue Bottle Equilibrium   |   Blue Bottle & Stop Light Reaction  by  Irwin Talesnick.

(2015-09-18)   Detecting Metallic Cations

 Leopold Gmelin 
 (1788-1853)  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.

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 still working on this one...

Wikipedia :   Ferroxyl indicator solution   |   Red prussiate   |   Leopold Gmelin (1788-1853)

(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.

The Dehydration of Sucrose  (RSC)   |   Dehydration of Sugar by H2SO4  (NCSU lecture demonstration)
Videos :   Dehydration of Sugar (Black Snake Experiment)   |   Don't try this at home: Sulfuric Acid and Sugar

(2011-08-27)   Waterlock :  Extreme Water Retention
1 g of  sodium polyacrylate  can hold  825 mL  of water.

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 still working on this one...

Wikipedia :   Sodium polyacrylate   |   Superabsorbent polymer
Videos :   Vanishing Water (The Trick)   &   Vanishing Water Revealed  by  Edward Kent

(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.

United Nuclear
Video :   Chemical fire  (Ammonium nitrate and zinc, ignited with HCl)

(2011-09-06)   Nitrogen Triiodide
An explosive set off by the touch of a feather or by  alpha radiation.

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 still working on this one...

Wikipedia :   Nitrogen triiodide 
Video :   Nitrogen Triiodide Detonation

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