Fluorine, colour preparation

Iodide ions reduce Cu to Cu , and attempts to prepare copper(ll) iodide therefore result in the formation of Cul. (In a quite analogous way attempts to prepare copper(ll) cyanide yield CuCN instead.) In fact it is the electronegative fluorine which fails to form a salt with copper(l), the other 3 halides being white insoluble compounds precipitated from aqueous solutions by the reduction of the Cu halide. By contrast, silver(l) provides (for the only time in this triad) 4 well-characterized halides. All except Agl have the rock-salt structure (p. 242). Increasing covalency from chloride to iodide is reflected in the deepening colour white yellow, as the... 

Barium Arsenide, Ba3As2.—By passing arsine over barium oxide at red heat Soubeiran 4 obtained a mixture of arsenide and arsenite. Lebeau 6 prepared the pure arsenide by reduction of barium arsenate with carbon in an electric furnace. Barium arsenide is very similar in properties to the arsenides of calcium and strontium it is slightly darker in colour, more readily fusible and more reactive chemically. Its density at 15° C. is 4-1. It burns spontaneously in fluorine, chlorine or bromine vapour. In oxygen it burns at about 300° C. and in sulphur vapour at dull red heat. 

In the preparation of binary fluorides using the general method for the synthesis of polymeric binary fluorides [1] it was noted that when an excess of Lewis acid (beyond the stoichiometric amount) was added to binary fluorides in aHF, a coloured solution resulted without immediate loss of fluorine. This coloured solution contains solvated fluorospecies obtained by the action of excess of Lewis acid on the binary fluoride, probably by removal of F from it. In the case of NiF4 the simplest cationic species would be [NiF3(HF)v]+ [15]. 

Transfer 2.4 ml of the buffered alizarin and 20 ml of distilled water to a 50 ml beaker. Add 1 ml of test solution and mix. Finally add 2 ml of cerous nitrate solution and mix again. Prepare a similar blank solution. When fluorine is present a mauve colour will be developed in the test solution compared with a pink colour in the blank. If a semi-quantitative estimation of fluorine is required measure the optical density of the test solution against the blank at 600 nm in 10 mm cells. Useful calibration figures are given below ... 

Transfer the remaining 100 ml of distillate to a Nessler cylinder and add an amount of 0 05N hydrochloric acid to make the total acidity equal to 5 0 ml of 0 05N acid. Prepare a control cylinder containing 5 0 ml of 0 05N hydrochloric acid and water and add to both test and control cylinders 2 ml of 0 01 per cent alizarin S solution. From a burette which can be read to 0 02 ml add to the test cylinder a solution of thorium nitrate (approximately 0 25 g per litre) until a slight pink colour persists as compared with the yellow of the control cylinder. Add an exactly similar volume of the thorium nitrate solution to the control cylinder, which then becomes more pink than the test solution. Then add slowly, from a suitable burette, standard solution of sodium fluoride (0 0221 g of NaF per litre 1 ml = 10 / g of fluorine) until the tints of... 

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