Iodate is a salt of iodic acid, which contains triangular pyramidal iodate ions—IO³−, in which the valence of iodine is +5.
Copper iodate is an inorganic compound with the chemical formula Cu(IO3)2, which is a green monoclinic crystal. The relative density is 5.241 (15 oC). The solubility volume constant of copper iodate refers to the equilibrium state of copper iodate dissolved in water at a certain temperature, the product of ion concentration, namely Ksp. Ksp is an important chemical parameter, which can be used to predict the concentration of ions in the solution, thus helping us understand the trends and results of chemical reactions.
The solubility volume constant of copper iodate is a very important parameter, which can be used to predict the solubility of copper iodate in water. At a certain temperature, the solubility of copper iodate is proportional to its solubility volume constant. The larger the solubility volume constant is, the greater the solubility of copper iodate in water is. Therefore, we can predict the solubility of copper iodate in water by measuring its solubility volume constant.
1. Experimental Principle
Cu(IO3)2 is an insoluble strong electrolyte. In its saturated solution, there is an equilibrium as follows:
At a certain temperature, the product of the square of Cu2+ concentration and IO3- concentration in the above equilibrium solution is a constant:
Ksp is called the solubility product constant. Like other equilibrium constants, the solubility product constant is a function of temperature and changes with temperature. Therefore, if the Cu2+ concentration and IO3- concentration in the Cu(IO3)2 saturated solution can be measured at a certain temperature, the Ksp at that temperature can be obtained.
In this experiment, a copper iodate saturated solution was prepared by the action of copper sulfate and potassium iodate, and then Cu2+ in the saturated solution was used to react with excess NH3.H2O to generate a dark blue complex ion [Cu(NH3)4]2+. Ions have strong absorption of light with a wavelength of 600 nm, and at a certain temperature, the degree of its absorption of light (that is, the absorbance A) is proportional to the concentration of the solution. Therefore, the absorbance of the complex ion [Cu(NH3)4]2+ solution generated by the interaction of Cu2+ and excess NH3·H2O in the copper iodate saturated solution was measured by a spectrophotometer, and the working curve (also known as the standard curve) was used to calculate the concentration of Cu2+ in the saturated solution.
The drawing of the working curve: prepare a series of standard solutions with different concentrations of [Cu(NH3)4]2+, determine the absorbance of each solution in the standard series by spectrophotometer, and then draw the graph with absorbance A as ordinate and a series of Cu2+ concentrations as the abscissa, and the straight line obtained is the working curve.
Finally, according to the relationship between the concentration of Cu2+ and the concentration of IO3- in the equilibrium of precipitation and dissolution, the solubility product constant Ksp of copper iodate can be obtained.
2. Instruments and Reagents
1) Instruments
721W spectrophotometer, cuvette (1 cm), beaker, pipette, funnel, quantitative filter paper, lens paper, volumetric flask (50 mL), thermometer, and bench scale.
2) Reagents
CuSO4·5H2O (s), KIO3 (s), NH3·H2O (1:1), CuSO4 (0.1000 mol·L-1), BaCl2 (0.1 mol·L-1).
3. Experimental Content
1) Drawing of the Working Curve (Standard Curve)
Accurately remove the CuSO4 (0.1000 mol·L-1) standard solution of 0.40 mL, 0.80 mL, 1.20 mL, 1.60 mL and 2.00 mL into the 50 mL volumetric flask numbered 1~5 with a pipette, then add 4.00 mL NH3·H2O (1:1) to the volumetric flask, shake well, dilute it to the scale with distilled water, and shake well.
With pure solvent distilled water as the reference solution, select a 1 cm cuvette, select the incident light wavelength as 600 nm, measure the absorbance of each numbered solution with a spectrophotometer, and the data are listed in Table 1.
2) Preparation of Cu(IO3)2 Solid
Weigh 2.0 g CuSO4·5H2O (s) and 3.4 g KIO3 (s) and react with the appropriate amount of water to obtain Cu(IO3)2 precipitate, wash the precipitate with distilled water until it does not contain SO42-.
3) Preparation of Cu(IO3)2 Saturated Solution
In the Cu(IO3)2 solid without SO42- after the above washing, add 80 mL distilled water, which is prepared as a saturated solution of Cu(IO3)2, then filter the saturated solution with a dry double-layer quantitative filter paper, and collect the filtrate in a dry beaker.
4) Determination of Cu2+ Concentration in Cu(IO3)2 Saturated Solution
Accurately remove the 20.00 mL filtered Cu(IO3)2 saturated solution into the 50 mL capacity bottle with a pipette, add 4.00 mL NH3·H2O (1:1), shake well, dilute it to the scale with distilled water, and then shake well. Then the absorbance of the solution was determined by spectrophotometer with pure solvent distilled water as a reference solution, 1 cm colorimetric plate, and an incident light wavelength of 600 nm. The concentration of Cu2+ in saturated solution is calculated according to the working curve.
According to the relationship between Cu2+ concentration and IO3- concentration in Cu(IO3)2 (s)
Cu2+( aq )+2IO3- (aq) equilibrium, the solubility product Ksp of copper iodate can be calculated.
4. Data Recording and Processing
1) List the working curve measurement data in Table 1.
Table 1 Absorbance at different concentrations
| Serial number | 1 | 2 | 3 | 4 | 5 |
| VCuSO4/mL | 0.40 | 0.80 | 1.20 | 1.60 | 2.00 |
| CCu2+/mol·L-1 | |||||
| Absorbance A |
2) Draw the working curve (standard curve) with the absorbance A as the ordinate and the Cu2+ concentration as the abscissa.
3) Calculate the Cu2+ concentration in the Cu(IO3)2 saturated solution according to the working curve, and calculate the solubility product Ksp of copper iodate.
5. Matters Needing Attention
1) Pipettes must be used exclusively.
2) Pay attention to the correct operation of the pipette.
3) When using a volumetric flask to prepare a standard solution, the volume must be determined strictly according to the scale of the container.
4) Pay attention to the way and direction of the cuvette and the amount of solution added to the cuvette.
5) Reasonable selection of a reference solution.
6) Use the spectrophotometer correctly.
7) The waste liquid generated in the experiment should be collected and treated in a centralized manner.
