Experiments yellow

Purification of anthracene. Dissolve 0-3 g. of crude anthracene (usually yellowish in colour) in 160-200 ml. of hexane, and pass the solution through a column of activated alumina (1 5-2 X 8-10 cm.). Develop the chromatogram with 100 ml. of hexane. Examine the column in the hght of an ultra-violet lamp. A narrow, deep blue fluorescent zone (due to carbazole, m.p. 238°) will be seen near the top of the column. Immediately below this there is a yellow, non-fluorescent zone, due to naphthacene (m.p. 337°). The anthracene forms a broad, blue-violet fluorescent zone in the lower part of the column. Continue the development with hexane until fluorescent material commences to pass into the filtrate. Reject the first runnings which contain soluble impurities and yield a paraffin-hke substance upon evaporation. Now elute the column with hexane-benzene (1 1) until the yellow zone reaches the bottom region of the column. Upon concentration of the filtrate, pure anthracene, m.p. 215-216°, which is fluorescent in dayhght, is obtained. The experiment may be repeated several times in order to obtain a moderate quantity of material. 

In a number of cases, identifications have been extremely difficult, because the materials were synthetic and knowledge of their existence had actually been lost. For example, several rather commonly encountered synthetic pigments, such as the lead-tin yellow often found in Renaissance and Baroque paintings, were originally misidentified or left unidentifiable until extensive research, including analyses of elemental composition and chemical and physical properties, and repHcation experiments, led to proper identification of the material and its manufacturing process. 

Consumers expectations depend on several factors including cultural background, past experiences, desire for color coordination, esthetic appeal, local customs, fads, etc. Thus, eg, a Texas red hot sold ia the South is often colored quite differently than one sold ia the North, Midwesterners prefer butter with a deep yellow color, and on birthdays the decoration on a boy s cake are often blue and those on a gid s are often pink. 

The crucial experiment suggesting that the H2 molecule might act as a dihapto ligand to transition metals was the dramatic observation that toluene solutions of the deep purple coordinatively unsaturated 16-electron complexes [Mo(CO)3(PCy3)2] and [W(CO)3-(PCy3)2l (where Cy = cyclohexyl) react readily and cleanly with Ha (I atm) at low temperatures to precipitate yellow crystals of [M(CO)3H2(PCy3)2] in 85-95% yield. The... 

The most satisfactory test for caramel is to shake with Fuller s earth, as recommended - by Crampton and Simons. If the colour is due to caramel and a grade of I uller s earth is used, which experience has proved suitable, the solution, after filtering, is yellow or colourless. This test does not positively identify the colour, as some other brown substances may give similar reactions, but no such substance is liable to be present in vanilla extract. 

B g (0 mol) of p-eminophenol hydrochloride is dissolved in 500 cc of water and added to 99 g (0.5 mol) of 4,7-dichloroquinoline. After a few minutes of warming in a steam bath, 4-(4 -hydroxyanilino)-7-chloroquinoline hydrochloride, of sufficient purity for use in further experiments, precipitates as a yellow crystalline solid. Recrystallized from methanol, the MP Is over 300. ... 

EL experiments showed that the yellow-emitting LEDs prepared from LPPP 12 exhibit quite remarkable characteristics (single layer construction ITO/LPPP 12/Ca quantum efficiency ca. 1.0%, applied voltage 4-6 V 135]). These figures are in the range of the best values described hitherto for polymeric emitters in a single layer arrangement, for example, poly(pcira-phenylenevinylene) PPV and PPV derivatives. 

A solution of 3-oxatetracyclo[3.2.0.02 7.04 f,]heptane (941 mg, 10 mmol) in anhyd benzene (10 mL), that had been treated with basic alumina prior to the experiment, was heated in a sealed tube for 4 h at 100 C. After cooling, Et2G (10 mL) was added. The mixture was chromatographed (silica gel, 30 g, Et20/pentane 7 3) to yield benzene as the first fraction and 900 mg (95%) of product. After careful evaporation of the Et20/pentane mixture, the product was purified by distillation to give a light yellow oil. 

FIGURE 8.31 An experiment to illustrate osmosis. Initially, the tube contained a sucrose solution and the beaker contained pure water the initial heights of the two liquids were the same. At the stage shown here, water has passed into the solution through the membrane by osmosis, and the level of solution in the tube has risen above that of the pure water. The large inset shows the molecules in the pure solvent (below the membrane) tending to join those in the solution (above the membrane) because the presence of solute molecules there has led to increased disorder. The small inset shows just the solute molecules the yellow arrow shows the direction of flow of solvent molecules. 

Schematic view of Miiiikan s oii drop experiment. An atomizer generated a fine mist of oil droplets (yellow circles). Bombarding the dropiets with X rays gave some of them extra negative charge orange circle). In the presence of sufficient eiectricai force, these negativeiy charged droplets could be suspended in space. ...

If we were to conduct a second solubility experiment in which solutions of KI and NaN03 were mixed, we would find that no precipitate forms. This demonstrates that K and NO3 ions do not form a solid precipitate, so the bright yellow precipitate must be lead(II) iodide, Pbl2. As the two salt solutions mix, cations and r anions combine to produce lead(II) iodide, which precipitates from the solution. On standing, the yellow precipitate settles, leaving a colorless solution that contains potassium cations and nitrate anions. The molecular blowups in Figure depict these solutions at the molecular level. 

The complex has been separated by ion exchange and characterised by direct analysis . The complex has a distinctive absorption spectrum (Fig. 11), quite unlike that of Np(V) and Cr(III). The rate coefficient for the first-order decomposition of the complex is 2.32 x 10 sec at 25 °C in 1.0 M HCIO. Sullivan has obtained a value for the equilibrium constant of the complex, K = [Np(V) Cr(III)]/[Np(V)][Cr(III)], of 2.62 + 0.48 at 25 °C by spectrophotometric experiments. The associated thermodynamic functions are AH = —3.3 kcal. mole" and AS = —9.0 cal.deg . mole . The rates of decay and aquation of the complex, measured at 992 m/t, were investigated in detail. The same complex is formed when Np(VI) is reduced by Cr(II), and it is concluded that the latter reaction proceeds through both inner- and outer-sphere paths. It is noteworthy that the substitution-inert Rh(lII), like Cr(III), forms a complex with Np(V) °. This bright-yellow Np(V) Rh(III) dimer has been separated by ion-exchange... 

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