Into a 250 ml. Claisen flask place 72 g. of cinnamic acid and 60 g. (37 ml.) of redistilled thionyl chloride. Stopper the side arm, fit the flask with a reflux condenser the top of which is connected to a gas absorption device, and mount the entire apparatus at an angle so that the condensate will not run into the side arm. Heat the mixture on a water bath, cautiously at first, until hydrogen chloride ceases to be evolved (about 1 hour), allow to cool, and add 47 g. of pure (e.g., A.R.) phenol. Heat the mixture on a water bath until no further evolution of hydrogen chloride is observed (about 1 hour). Then place the apparatus on an asbestos-centred wire gauze and heat the flask until the contents are brought just to the reflux temperature in order to complete the reaction : do not heat unduly long as prolonged heating leads to loss of product due to decomposition and polymerisation. Allow the reaction -mixture to cool and distil under diminished pressure ; collect the fraction of b.p. 190-210°/15 mm. This solidifies to a pale yellow solid, m.p. 66-69°, weighing 98 g. Grind it to a powder in a glass mortar and wash the powder with 250 ml. of cold 2 per cent, sodium bicarbonate solution. Recrystallise from rectified spirit (150 ml.) : 81 g. of pure phenyl cinnamate (white crystals) of m.p. 75-76° are obtained.
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Senin, 02 Agustus 2010
PHENYLHYDRAZINE
Dissolve 35 g. of sodium nitrite in 75 ml. of water, cool to 0-3°, and run in the cold solution from a separatory funnel, the stem of which reaches nearly to the bottom of the flask. During the addition of the nitrite solution (ca. 20 minutes), stir vigorously and keep the temperature as near 0° as possible by the frequent addition of crushed ice. There should be a slight excess of nitrous acid (potassium iodide- starch paper test) at the end of 10 minutes after the last portion of nitrite is added.
In the meantime, prepare a sodium sulphite solution as follows. In a 2-litre beaker or bolt-head flask place 50 g. of sodium hydroxide (2) and add 500 ml. of water. When the sodium hydroxide has dissolved, add 112-5 g. of recrystallised sodium bisulphite (3), and stir mechanically until the solid has dissolved. Cool the resulting solution to about 25° and add a few drops of phenolphthalein indicator solution. Introduce small quantities of sodium bisulphite until the pink colour of the solution just disappears, then stir in a further 12 g. of sodium bisulphite (the total weight required should not exceed 135-140 g.). Cool this solution, with stirring, to about 5° by immersion in an ice bath, then add about 60 g. of crushed ice. Run in the ice-cold diazonium solution as rapidly as possible, while stirring vigorously.
The reaction mixture immediately acquires a bright orange-red colour. Slowly heat the solution to 60-70° on a water bath and maintain this temperature for 30-60 minutes, i.e., until the colour becomes quite dark. Acidify the solution to litmus with con- centrated hydrochloric acid (40-50 ml. are required) ; continue the heating on a boiling water bath until the colour becomes much lighter and in any case for 4-6 hours. If any solid is present, filter the solution. To the hot, clear solution add, with stirring, 500 ml. of concentrated hydrochloric acid ; cool, first in running water, and then in a freezing mixture to 0°. The phenylhydrazine hydrochloride separates as yellowish or pinkish crystals. Collect them on a Buchner funnel, drain, wash with 25 ml. of dilute hydrochloric acid (1:3) , and press well with a large glass stopper (4). Liberate the free base by adding to the phenylhydrazine hydrochloride 125 ml. of 25 per cent, sodium hydroxide solution. Extract the phenyl- hydrazine with two 40 ml. portions of benzene, dry the extracts with 25 g. of sodium hydroxide pellets or with anhydrous potassium carbonate : thorough drying is essential if foaming in the subsequent distillation is to be avoided. Most of the benzene may now be distilled under atmo- spheric pressure, and the residual phenylhydrazine under reduced pressure. For this purpose, fit a small dropping funnel to the main neck of a 100 ml. Claisen flask (which contains a few fragments of porous porcelain) and assemble the rest of the apparatus but do not connect the " Perkin triangle " to the pump. Run in about 40 ml. of the benzene, solution into the flask, heat the latter in an air bath so that the benzene distils over steadily. Allow the remainder of the benzene solution to run in from the dropping funnel as fast as the benzene itself distils over. When all the benzene solution has been introduced into the flask, close the stopcock on the funnel, and continue the heating until the temperature on the thermometer reads about 90°. Allow to cool. Replace the dropping funnel by a rubber stopper carrying a capillary tube reaching to the bottom of the flask, and distil under diminished pressure.
Collect the phenylhydrazine at 137-138°/18 mm. (or at 119-120°/12 mm.). The yield of almost colourless liquid is 70 g. ; it crystallises on cooling in ice and then melts at 23°. Phenylhydrazine slowly darkens on exposure to light.
CAUTION. Phenylhydrazine is highly poisonous and produces unpleasant burns in contact with the skin. Wash off immediately any liquid which has come into contact with the skin first with 2 per cent, acetic acid, then with soap and water.
Notes.
(1) External cooling may be dispensed with if more ice is added.
(2) This weight assumes 100 per cent, purity of the sodium hydroxide. If the commercial solid is used, its purity should be determined and a corresponding adjustment made in the weight.
(3) The sodium sulphite solution may also be prepared by dissolving 100 g. of pure (or a corresponding quantity of commercial) sodium hydroxide in about 125 ml. of water, and then diluting to 750 ml. The flask is cooled in running water, a few drops of phenolphthalein indicator are added, and sulphur dioxide passed in until the pink colour just disappears (it is advisable to add a further 1-2 drops of the indicator at this point) and then for 2-3 minutes longer. It is best to remove a sample for test from time to time, dilute with 3-4 volumes of water, and test with 1 drop of phenolphthalein.
(4) If desired, the phenylhydrazine hydrochloride may be purified by recrystallisation. The crude hydrochloride is boiled with 6 times its weight of water and a few grams of decolourising carbon. After filtering, a volume of concentrated hydrochloric acid equal in volume to one-third of the solution is added, and the mixture cooled to 0°. Pure white crystals are obtained in 85-90 per cent, yield.
STANDARD EDTA SOLUTIONS
Disodium dihydrogenethylenediaminetetra-acetate of analytical reagent quality is available commercially but this may contain a trace of moisture. After drying the reagent at 80 OC its composition agrees with the formula Na2H2C1,H1 20,N2,2H20 (relative molar mass 372.24), but it should not be used as a primary standard. If necessary, the commercial material may be purified by preparing a saturated solution at room temperature: this requires about 20 g of the salt per 200 mL of water. Add ethanol slowly until a permanent precipitate appears; filter. Dilute the filtrate with an equal volume of ethanol, filter the resulting precipitate through a sintered glass funnel, wash with acetone and then with diethyl ether. Air-dry at room temperature overnight and then dry in an oven at 80 OC for at least 24 hours. Solutions of EDTA of the following concentrations are suitable for most experimental work: O.lM, 0.05M, and 0.01M. These contain respectively 37.224 g, 18.612 g, and 3.7224 g of the dihydrate per litre of solution. As already indicated, the dry analytical grade salt cannot be regarded as a primary standard and the solution must be standardised; this can be done by titration of nearly neutralised zinc chloride or zinc sulphate solution prepared from a known weight
of zinc pellets, or by titration with a solution made from specially dried lead nitrate. The water employed in making up solutions, particularly dilute solutions, of EDTA should contain no traces of multicharged ions. The distilled water normally used in the laboratory may require distillation in an all-Pyrex glass apparatus or, better, passage through a column of cation exchange resin in the sodium form - the latter procedure will remove al1 traces of heavy metals. De-ionised water is also satisfactory; it should be prepared from distilled water since tap water sometimes contains non-ionic imiuriiies not removed by an ion exchange column. The solution may be kept in Pyrex (or similar borosilicate glass) vessels, which have been thoroughly steamed out before use. For prolonged storage in borosilicate vessels, the latter should be boiled with a strongly alkaline, 2 per cent EDTA solution for several hours and then repeatedly rinsed with de-ionised water. Polythene bottles are the most satisfactory, and should always be employed for the storage of very dilute (e.g. 0.001 M) solutions of EDTA. Vessels of ordinary (soda) glass should not be used; in the course of time such soft glass containers will yield appreciable amounts of cations (including calcium and magnesium) and anions to solutions of EDTA. Water purified or prepared as described above should be used for the preparation of al1 solutions required for EDTA or similar titrations.
DETERMINATION OF COPPER AS THE DIETHYLDITHIOCARBAMATE COMPLEX
Sodium diethyldithiocarbamate (B) reacts with a weakly acidic or ammoniacal solution of copper(I1) in low concentration to produce a brown colloidal suspension of the copper(I1) diethyldithiocarbamate. The suspension may be extracted with an organic solvent (chloroform, carbon tetrachloride or butyl acetate) and the coloured extract analysed spectrophotometrically at 560 nm (butyl acetate) or 435 nm (chloroform or carbon tetrachloride). Many of the heavy metals give slightly soluble products (some white, some coloured) with the reagent, most of which are soluble in the organic solvents mentioned. The selectivity of the reagent may be improved by the use of masking agents, particularly EDTA. The reagent decomposes rapidly in solutions of low pH.
Procedure. Dissolve 0.0393 g of pure copper(I1) sulphate pentahydrate in 1 L of water in a graduated flask. Pipette 10.0 mL of this solution (containing about 100 pg Cu) into a beaker, add 5.0 mL of 25 per cent aqueous citric acid solution,render slightly alkaline with dilute ammonia solution and boil off the excess of ammonia; alternatively, adjust to pH 8.5 using a pH meter. Add 15.0mL of 4 per cent EDTA solution and cool to room temperature. Transfer to a separatory funnel, add 10mL of 0.2 per cent aqueous sodium diethyldithio- carbamate solution, and shake for 45 seconds. A yellow-brown colour develops in the solution. Pipette 20 mL of butyl acetate (ethanoate) into the funnel and shake for 30 seconds. The organic layer acquires a yellow colour. Cool, shake for 15 seconds and allow the phases to separate. Remove the lower aqueous layer; add 20 mL of 5 per cent sulphuric acid (v/v), shake for 15 seconds, cool, and separate the organic phase. Determine the absorbance at 560 nm in 1.0 cm absorption cells against a blank. Al1 the copper is removed in one extraction. Repeat the experiment in the presence of 1 mg of iron(II1); no interference can be detected.
GLASSWARE
Cleaning of glass apparatus. Before describing graduated apparatus in detail, reference must be made to the important fact that al1 such glassware must be perfectly clean and free from grease, otherwise the results will be unreliable. One test for cleanliness of glass apparatus is that on being filled with distilled water and the water withdrawn, only an unbroken film of water remains. If the water collects in drops, the vesse1 is dirty and must be cleaned.
Various methods are available for cleaning glassware. Many commercially available detergents are suitable for this purpose, and some manufacturers market special formulations for cleaning laboratory glassware; some of these, e.g. 'Decon 90' made by Decon Laboratories of Portslade, are claimed to be specially effective in removing contamination due to radioactive materials. 'Teepol' is a relatively mild and inexpensive detergent which may be used for cleaning glassware. The laboratory stock solution may consist of a 10 per cent solution in distilled water.
For cleaning a burette, 2 mL of the stock solutiondiluted with 50 mL of distilled water are poured into the burette, allowed to stand for 4 to 1 minute, the detergent run off, the burette rinsed three times with tap water, and then several times with distilled water. A 25 mL pipette may be similarly cleaned using 1 mL of the stock solution diluted with 25-30 mL of distilled water. A method which is frequently used consists in filling the apparatus with 'chromic acid cleaning mixture' (CARE), a nearly saturated solution of powdered sodium dichromate or potassium dichromate in concentrated sulphuric acid, and allowing it to stand for several hours, preferably overnight; the acid is then poured off, the apparatus thoroughly rinsed with distilled water, and allowed to drain until dry. [It may be mentioned that potassium dichromate is not very soluble in concentrated sulphuric acid (about 5 g per litre), whereas sodium dichromate (Na2Cr20,,2H20) is much more soluble (about 70 g per litre); for this reason, as well as the fact that it is much cheaper, the latter is usually preferred for the preparation of 'cleaning mixture'. From time to time it is advisable to filter the sodium dichromate-sulphuric acid mixture through a little glass wool placed in the apex of a glass funnel: small particles or sludge, which are often present and may block the tips of burettes, are thus removed.
A more efficient cleaning liquid is a mixture of concentrated sulphuric acid and fuming nitric acid; this may be used if the vessel is very greasy and dirty, but must be handled with extreme caution. A very effective degreasing agent, which it is claimed is much quicker-acting than 'cleaning mixture' is obtained by dissolving 100 g of potassium hydroxide in 50mL of water, and after cooling, making up to 1 litre with industrial methylated spirit.
Amazing detergent
What you need
To do this activity you will need
- a saucer
- milk
- food colouring (four different colours)
- detergent.
What to do
- Fill the saucer with milk.
- Add one drop of each food colour to the milk around the edge of the saucer.
- Add one drop of detergent into the centre of the saucer.
What's happening
The colours swirl and zoom around the saucer.
Milk stays together as one liquid because of surface tension. This acts like a skin and keeps the milk in a puddle. When you add the detergent, it breaks the surface tension of the milk in one spot.
The pull of the surface tension from the milk at the edge of the saucer causes the milk in the centre to move to the outside, taking the colours along with it.
The colours keep moving until the detergent stops affecting the milk.
Sabtu, 20 Maret 2010
ELECTRONEGATIVITY
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.
What happens if two atoms of equal electronegativity bond together?
Consider a bond between two atoms, A and B. Each atom may be forming other bonds as well as the one shown - but these are irrelevant to the argument. If the atoms are equally electronegative, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average half way between the two atoms. To get a bond like this, A and B would usually have to be the same atom. You will find this sort of bond in, for example, H2 or Cl2 molecules. This sort of bond could be thought of as being a "pure" covalent bond - where the electrons are shared evenly between the two atoms.
What happens if B is slightly more electronegative than A?
B will attract the electron pair rather more than A does. That means that the B end of the bond has more than its fair share of electron density and so becomes slightly negative. At the same time, the A end (rather short of electrons) becomes slightly positive. In the diagram, " Defining polar bonds This is described as a polar bond. A polar bond is a covalent bond in which there is a separation of charge between one end and the other - in other words in which one end is slightly positive and the other slightly negative. Examples include most covalent bonds. The hydrogen-chlorine bond in HCl or the hydrogen-oxygen bonds in water are typical. What happens if B is a lot more electronegative than A? In this case, the electron pair is dragged right over to B's end of the bond. To all intents and purposes, A has lost control of its electron, and B has complete control over both electrons. Ions have been formed. In this case, the electron pair is dragged right over to B's end of the bond. To all intents and purposes, A has lost control of its electron, and B has complete control over both electrons. Ions have been formed. Lithium iodide, on the other hand, would be described as being "ionic with some covalent character". In this case, the pair of electrons hasn't moved entirely over to the iodine end of the bond. Lithium iodide, for example, dissolves in organic solvents like ethanol - not something which ionic substances normally do.
CHEMICAL BOND
Ionic bonds arise from elements with low electronegativity(almost empty outer shells) reacting with elements with high electronegativity (mostly full outer shells). In this case there is a complete transfer of electrons.
A well known example is table salt, sodium chloride. Sodium gives up its one outer shell electron completely to chlorine which needs only one electron to fill its shell. Thus, the attraction between these atoms is much like static electricity since opposite charges attract.
Covalent bond
Covalent bonds involve a complete sharing of electrons and occurrs most commonly between atoms that have partially filled outer shells or energy levels. Thus if the atoms are similar in negativity then the electrons will be shared. Carbon forms covalent bonds. The electrons are in hybrid orbitals formed by the atoms involved as in this example: ethane. Diamond is strong because it involves a vast network of covalent bonds between the carbon atoms in the diamond.
Polar covalent bond
These bonds are in between covalent and ionic bonds in that the atoms share electrons but the electrons spend more of their time around on atom versus the others in the compound. This type of bond occurs when the atoms involved differ greatly in electronegativity. The most familiar example is water. Oxygen is much more electronegative than hydrogen, and so the electrons involved in bonding the water molecule spend more time there. The fact that water is a polar covalently bonded moleccule has a number of implications for molecules that are disolved in water. In particular, molecules with polar covalent bods can break apart when they encounter water molecules. They are broken apart because of the electrical attraction between the dissimilar charges of the molecules. Also, since ionically bonded molecules involve ions with opposite charges, water with its polar covalent bonds can separate ions from each other and then surround the ions which prevents them from recombining. The properties of water all relate to this polar covalent bonding. Indeed the sorts of so called hydrophilic and hydrophobic interactions water has with varios organic compounds depend on the nature of the polar covalent bond in water.
Hydrogen bond
The fact that the oxygen end of a water molecule is negatively charged and the hydrogen end positively charged means that the hydrogens of one water molecule attract the oxygen of its neighbor and vice versa. This is because unlike charges attract. This largely electrostatic attraction is called a hydrogen bond and is important in determining many important properties of water that make it such an important liquid for living things. Water can also form this type of bond with other polar molecules or ions such as hydrogen or sodium ions. Further, hydrogen bonds can occurr within and between other molecules. For instance, the two strands of a DNA molecule are held together by hydrogen bonds. Hygrogen bonding between water molecules and the amino acids of proteins are involved in maintaining the protein's proper shape.
from http://staff.jccc.net/pdecell/chemistry/bonds.html
Selasa, 16 Maret 2010
WHAT IS INORGANIC CHEMISTRY
The term organic has traditionally referred only to animal or plant matter. Therefore, there is a common misconception that organic chemistry always refers to life processes, or that inorganic chemistry applies to everything that does not. This assumption is inaccurate. Many chemical processes veer away from this line of thinking. There are many chemical life processes that depend on inorganic chemical processes.
There are exceptions to every rule. Although carbon is the main common element in organic chemistry, inorganic chemical compounds can contain carbon, too. For example, carbon monoxide and carbon dioxide both contain carbon, but are inorganic compounds. Carbon dioxide, in particular, is also very important to chemical processes necessary for life, especially plant life. The truth is that the lines between inorganic and organic chemistry are often blurred.
There are many branches of inorganic chemistry available for specialization. Geochemistry is the study of the chemicals of the Earth and other planets. It covers the chemical compositions of rocks and soil. Within the field of geochemistry, there are several subfields. These subfields include isotope geochemistry, cosmochemistry and biogeochemistry.
Another type of inorganic chemistry is physical chemistry, which relates to the concept of physics in chemical systems. This field is also sometimes called physicochemistry. It uses the principles of thermodynamics, quantum chemistry and kinetics as its basis.
On the other hand, bioinorganic chemistry is the study of compounds containing metal-carbon bonds within biological systems. This is a particularly interesting branch of inorganic chemistry because it also incorporates aspects of organic chemistry into it. Bioinorganic chemistry focuses on the pretense of metal ions in biochemical processes.
Inorganic chemistry lends itself to many different industries, including education, environmental science, and government agencies. A scientist who focuses on inorganic chemistry might create or improves formulas for household cleansers. He may also work in chemical research, coming up with new ways to manipulate the properties of metallic elements into useful functions.
FROM http://www.wisegeek.com/what-is-inorganic-chemistry.htm
WHAT IS ANALYTICAL CHEMISTRY
Early analytical chemistry was mainly focused on identifying elements and compounds and discovering their attributes. Discovery gave way to systematic analysis, which took a giant step forward with the invention in the 1850’s of the first instrument for chemical analysis—flame emissive spectrometry—by Robert Bunsen, a German chemist who is better known for his invention of the Bunsen burner, and his colleague Gustav Kirchoff, a German physicist who is known for his 1862 coining the name "black body" radiation for an object that absorbs all of the electromagnetic radiation that reaches it.
Other separation processes were developed, including various kinds of chromatography such as paper, gas, and liquid; electrophoresis; crystallography; microfiltration; and other spectrometers, including atomic absorption spectrometers, infrared spectrometers, and mass spectrometers. Other changes in the field took place, for example, the extension of analytical chemistry allowing for bioanalytical chemistry to develop. Bioanalytics includes areas such as genomics, lipidomics, metabolomics, peptidomics, proteomics, and transcriptomics.
The traditional subdivisions of analytical chemistry followed the same paradigm as in statistical analysis: a qualitative approach that was focused on determining what elements and/or compounds were present and a quantitative approach that aimed to establish the precise amount of an element or compound in a given sample. Either, or both, of these approaches to analytical chemistry can be applied to materials in a variety of fields, including the food and beverage industry, the pharmaceutical industry, synthetic materials such as polymers, and natural materials, such as minerals and water samples. As the field grew, analytical chemistry also broadened to embrace applications of its techniques in forensics, and medicine.
Analytical chemists today use a wide variety of techniques in their analyses, including some involving robotics, digital microscopes, a Fourier transform infrared spectophotometers, chip-based technology, and chemometrics, for example. They also use techniques in which technologies are combined, resulting in approaches referred to as hyphenated or hybrid techniques, characteristically referred to by initials. Examples include CE-MS—capillary electrophoresis-mass spectrometry; GC-MS—gas chromatography-mass spectrometry; CE-UV—capillary electrophoresis-ultraviolet; and HPLC/ESI-MS—high performance liquid chromatography/electrospray ionization-mass spectrometry.
FROM http://www.wisegeek.com/what-is-analytical-chemistry.htm