Colour of solution

Nessler tubes Cylinders of thin glass, generally graduated, used for comparing turbidities and colours of solutions. 

A large number of miscellaneous characteristics are usually included in many official compendia to ascertain the purity, authenticity and identification of drugs—including sulphated ash, loss on drying, clarity and colour of solution, presence of heavy metals and specific tests. 

Substance being tested Indicator Colour of solution... 

Sodium thiosulphate solution yellow colour of solution discharged and sulphur precipitated, owing to reduction. 

Ammonium fluoride solution yellow colour of solution is discharged but no precipitate is produced, due to the formation of hexafluorocerate(IV) anions, [CeF6]2. ... 

In qualitative analysis copper is detected by precipitation as cupric sulphide from hydrochloric-acid solutions of its salts. To prevent the formation of a colloidal precipitate, the solution should be hot, and should contain excess of the acid. The sulphide is soluble in hot, dilute nitric acid, and in potassium-cyanide solution, but almost insoluble in solutions of alkali-metal sulphides. It dissolves to some extent in ammonium-sulphide solution. Other aids in the detection of copper are the blue colour of solutions of cupric-ammonia salts the reddish-brown precipitate of cupric ferrocyanide, produced by addition of potassium ferro-cyanide to cupric solutions the formation of an intense purple coloration by the interaction of hydrogen bromide and cupric salts, a very delicate reaction2 the formation of a bluish-green borax bead and the ready isolation of the metal from its compounds by the action of reducers. 

The colour of solutions and/or precipitates has to be interpreted from written or oral information. Interpretation of colour can be subjective, so you will need to gain sufficient experience using solutions of known content to establish how a particular colour appears to you. 

An antioxidant to stabilize the colour of solution could be added (0.02% sodium bisulfite or 0.5% cysteine). 

The visible and the near UV regions are characterized by absorption bands owing to intra-atomic d-d transitions. This kind of transition is specific for ions of transition metals with an incomplete d shell. Splitting of the d sub-levels in the ligand field creates a possibility of transitions between the levels due to absorption of appropriate radiation quanta. The colour of solutions of transition metal ions is connected with the intra-atomic d-d transitions. The transition metals are capable of forming coloured complexes even with colourless reagents, which do not contain chromophoric groups. 

Time of heating at 120° C min) Change in colour of solution by heating Concentration which carries a bacteriostatic effect on the dysentery bacillus... 

Colour of the crystalline salt the colours of solutions may deviate slightly depending on the concentration and the solvent.6 Synthetic preparation. 

The changing in colour of solution is measured in visible range and proportional to the quantity of sugar inside the sample. 

The time of initial colouration on mixing of reactants depends upon the temperature and protonic acid used. When HCl is used as a protonic acid, the colouration of solution occurs almost after 1 minute at room temperature and around 1-5°C it is 3-5 minutes. The sequence of colouration is light blue—blue green -> coppery tint green precipitates. 

The pale colour of solutions of Fe(III) nitrate or the ammonium iron(III) sulphate is reflected in the veiy weak absorption bands, similar to those of high spin Mn(II) salts. Spectra of Fe(IIl) chloride solution in HCI or in some oxygenated organic solvents are reported in both the visible and uv regions in J.Am.Chem.Socl3 951). It was concluded by the Authors that the tetrahedral FeCU was the main absorbing species. 

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