Bismuthyl ion

However, if there was sufficient amount of H+ ions in the solution, equilibrium shifted towards the left and bismuth remained in the solution as Bi3+. Therefore, during sonication activated water molecules were formed which reacted with Bi3+ ions. But instead of forming Bi(OH)3, they formed bismuthyl ions, BiO+, due to the fact that Bi(OH)3 was a weaker base, therefore hydrolysed readily to generate bismuthyl ion, BiO+. These steps could be summarised as under ... 

The amount of precipitated bismuth decreased as the concentration of bismuth salt increased (Table 9.16) and the duration of sonication required to bring about hydrolysis also increased. The initial reaction was spontaneous as per Eq. (9.111), which, however, seemed to be facilitated by ultrasonic cavitation at high concentration of bismuth. Since the H+ ions were also produced during the formation of bismuthyl ion, at the point where the sum of concentration of H+ ions present initially and formed by Eq. (9.110) was equal to the concentration required to shift the equilibrium of Eq. (9.111) towards left side, the hydrolysis did not occur even after sonication. 

The bismuthyl ion, BiO+ forms insoluble salts, like bismuthyl chloride, BiOCl, with most ions. If we want to keep bismuth ions in solution, we must acidify the solution, when the above equilibrium shifts towards the left. 

To 0.5 mg of the substance to be examined add 10 ml of dilute hydrochloric acid R or use 10 ml of the prescribed solution. Heat to boiling for 1 min. Cool and filter if necessary. This procedure should bring the most likely otherwise insoluble bismuth salt into solution. In the next step of analysis, 1 ml of the solution obtained is added to 20 ml of water R, upon which a white or slightly yellow precipitate is formed. Bismuth(lll) hydrolyzes water, forming the bismuthyl ion. 

There is considerable evidence for the association of Bi3+ ion with nitrate ions in aqueous solution. The nitrate ions appear to be mainly bidentate, and all members of the set Bi(N03) (H20)3 +. .. Bi(N03)4 appear to occur.70 From acid solution various hydrated crystalline salts such as Bi(N03)3 5H20, Bi2(S04)3 and double nitrates of the type M3[Bi(N03)6]2,24H20 can be obtained. Treatment of Bi203 with nitric acid gives bismuthyl salts such as BiO(N03) and Bi202(0H)(N03). Similar bismuthyl salts are precipitated on dilution of strongly acid solutions of various bismuth compounds. Bismuthyl salts are generally insoluble in water. 

---