Cadmium ions

The equivalent amount of cadmium ion exchanged for the silver ion can readily be determined by EDTA titration procedures. 

X 10 mol/L in 8 Mpotassium hydroxide at room temperature. In general it is believ ed tliat tlie solution process consists of anodic dissolution of cadmium ions in tlie form of complex hydroxides (see Cadmium compounds). 

Cadmium is rapidly oxidized by hot dilute nitric acid with the simultaneous generation of various oxides of nitrogen. Unlike the ziac ion, the cadmium ion is not markedly amphoteric, and therefore cadmium hydroxide [21041-95-2] Cd(OH)2, is virtually iasoluble ia alkaline media. However, the cadmium ion forms stable complexes with ammonia as well as with cyanide and haUde ions. The metal is not attacked by aqueous solutions of alkaU hydroxide. 

Because of the increasing emphasis on monitoring of environmental cadmium the detemiination of extremely low concentrations of cadmium ion has been developed. Table 2 Hsts the most prevalent analytical techniques and the detection limits. In general, for soluble cadmium species, atomic absorption is the method of choice for detection of very low concentrations. Mobile prompt gamma in vivo activation analysis has been developed for the nondestmctive sampling of cadmium in biological samples (18). 

Cadmium-ion solution. Dissolve about 6.0 g of analytical grade crystallised cadmium sulphate in 25 mL of Reagent I. 

DETERMINATION OF THE HALF-WAVE POTENTIAL OF THE CADMIUM ION IN 1 (If POTASSIUM CHLORIDE SOLUTION... 

Determine the half-wave potential from the current-voltage curve as described in Section 16.6 the value in 1M potassium chloride should be about — 0.60 vs S.C.E. Measure the maximum height of the diffusion wave after correction has been made for the residual current this is the diffusion current Id, and is proportional to the total concentration of cadmium ions in the solution. 

Standard cadmium ion solution. Prepare a standard cadmium ion solution containing ca 0.04 mg mL 1 Cd using hydrated cadmium sulphate. 

The effect of metal-ion catalysis (especially that of cadmium ion) in the above reaction has been studied628, and in Table 201 are listed the first-order rate coefficients for protodeboronation of 2,6-dimethoxybenzeneboronic acid in malonic acid-sodium malonate buffer or perchloric acid, observed in the absence ( ) or presence ( ) of cadmium ion, together with the second-order rate coefficients (k2) obtained by dividing the difference of these values by the cadmium ion concentration. The data of the first ten rows of Table 201 are plotted in Fig. 4 and the... 

Fig. 4. Variation of rate with pH for cadmium ion-catalyzed protodeboronation of 2,6-dimethoxy-...

Rows 12-16 in Table 201 show that the acceleration by cadmium ion is not linear with concentration, becoming proportionally less as the concentration is increased. The last entry shows the magnitude of the experimental error in the acid-catalysed portion of the reaction for this result now indicates that cadmium ion has no effect on the acid-catalysed reaction. 

Fig. 15-11 Effects of strong complexation on metal ion toxicity, (a) Increasing concentration of NTA, a strong multi-dentate complexing agent, decreases the toxicity of Cd to grass shrimp. All systems have equal concentrations of total Cd. (b) When the results are replotted showing survival as a function of Cd concentration, the data for all concentrations of NTA collapse to a single curve. (Reprinted with permission from W. G. Sunda et al. (1978). Effect of chemical speciation on toxicity of cadmium to grass shrimp, Palaemonetes pugio importance of free cadmium ions. Environ. Sci. Technol. 12,409-413, American Chemical Society.)...

Using the equilibrium constants below, calculate the concentrations of free (uncomplexed) cadmium ion in a freshwater with a chloride concentration of 15 mg/L, and in seawater containing 17 000 mg/L chloride. Ignore com-plexation with other ions. 

C04-0026. Cadmium ions are environmental pollutants found in mining waste, metal plating, water pipes, and industrial discharge. Cadmium ions replace zinc ions in biochemistry and cause kidney damage, high blood pressure, and brittle bones. Dissolved Cd " " impurities can be removed from a water sample... 

The wastewater contains Cd +, so an anion must also be present in the solution to balance the charge of the cadmium ions. Other species may exist as well. The problem asks only about the cadmium in the wastewater, so assume that any other ions are spectators. The sodium hydroxide solution contains Na and OH, so the major species in the treated wastewater include B.2 O, Cd ", OH", and Na. The equilibrium constant for the precipitation reaction is the inverse of for Cd (OH)2 ... 

The problem asks for the residual concentration of cadmium ions. In other words, what is the Cd ion concentration in the solution after the NaOH is added Before a concentration table can be completed,... 

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

To be specific, let us consider the global reaction between dissolved cadmium ions and thiourea molecules in ammonia solutions, which can be represented as... 

Changing the substrate from gold to silver has been shown to strongly affect the structure of the first few layers of CdS grown by ECALE. STM measurements carried out on the first CdS layer on Ag(lll) revealed a much less compact structure than the one found on Au(lll). This disparity was tentatively attributed to the different structure of the first S layer on Ag(l 11), as obtained by oxidative UPD from sulfide ion solutions, due to a higher affinity of sulfur for silver than for gold. The Cd layers were attained on S by reductive UPD from cadmium ion solutions. Precursors for both elements were dissolved in pyrophosphate/NaOH at pH 12 [43 5],... 

The exchange of Mo between the anions Mo(CN)g and Mo(CN)g has been investigated by the isotopic method ( Mo) and the separation methods (a) precipitation of Mo(CN)g with either ethanol or cadmium ions, and (b) precipitation of Mo(CN) with tetraphenylarsonium chloride. Complete exchange was observed by Wolfgang even with reactant concentrations 5x10 M. An estimate of the rate coefficient at 2 °C of >10 l.mole . sec has been sug-geMd. 

---