Sedimentary equilibrium in the system - solution. Solubility product in analytical practice is wide

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Sedimentary equilibrium in the system - solution. Solubility product in analytical practice is widely used the formation and dissolution of precipitates. The solubility of different substances in the same solvent or a substance in various solvents can vary within very wide limits. Quantitatively determine the solubility of substance content (concentration) in a saturated solution, ie that which is characterized by dynamic equilibrium provided constant temperature, the undissolved rational ovens usa substance (precipitate)? substance rational ovens usa in solution. All salts, including soluble, refer to the strong electrolytes. Because of this, during the deposition or dissolution rational ovens usa of soluble salts in aqueous solution rational ovens usa in equilibrium with the sediment are only ions of salt. The equation of dynamic equilibrium should rational ovens usa look. In equilibrium constant provided rational ovens usa the temperature per unit of time goes into solution so many compounds, which by this time of the solution precipitates. This dynamic heterogeneous equilibrium solubility product described rule. In a saturated solution at a constant temperature of product activities soluble electrolyte ions is constant and known solubility product of (DR). or (3.1), (3.2) where - according concentrations of cations and anions; and - the activity coefficients of cations and anions. Because soluble electrolyte solubility in water is very small, and the concentration of ions in solution will be low, and ionic strength of the solution will be close to zero. Therefore, rational ovens usa the activity coefficient of ions in such solutions will be equal to the unit or move toward it. Because of this, in terms of products solubility product of activities can instead take the product ion concentrations. . (3.3) This greatly simplifies the calculations solubility soluble compounds. The expression product of solubility soluble rational ovens usa compound that dissociates the equation to have a look. (3.4) Terms of sediment isolation and dissolving electrolyte - if, the supersaturated solution, precipitated; - If the solution is saturated, the system is in equilibrium; - If the solution is unsaturated, the precipitate dissolved. Precipitation is considered complete if the concentration of ions in solution does not exceed 10 -6 mol / L or 10 -4 g / l (limit of sensitivity of analytical scales). The value of the solubility product is used not only in solving issues related to the ions by precipitation in the form of soluble compounds, but also in determining the conditions of transfer of soluble precipitates in the solution. An important characteristic of soluble compounds is their solubility in different solvents. For binary sparingly soluble compounds solubility is calculated by equation (3.5) for soluble compounds such. (3.6) to dissolve sludge should reduce rational ovens usa the concentration of at least one of the ions, which is part of sparingly soluble compounds. This is possible due to: the formation of a weak electrolyte; formation of stable complex ions; binding of ions in volatile compound; changes in the degree of oxidation. Solving typical tasks Task 1. Determine the number of grams in 1 liter of ion saturated solution of barium orthophosphate. Calculate how to change the concentration of ions, if 1 liter of solution dissolved orthophosphate Sodium rational ovens usa 16,4h? . Solution. Ba 3 (PO 4) 2 - is sparingly soluble compounds which dissociates the equation. rational ovens usa Since one molecule of salt Ba 3 (PO 4) 3 2 formed ions and ions 2, then taking the salt concentration in the solution for x, we get and. Then. Calculate the solubility of the compound of the equation (3.6). The concentration of ions in solution is mol / L and in g / l g / l. The introduction of the salt solution Na 3 PO 4 can be assumed that the total concentration of ions in solution will be equal to the concentration of salt. The concentration of ions formed by the dissolution of Ba 3 (PO 4) 2, can be neglected because the solubility of this compound is very low. Define the molar concentration of salt Na 3 PO 4: g / mol; mol / l; mol / l. The expression product of the solubility of Ba 3 (PO 4) 2 after adding the salt solution Na 3 PO 4 will look. It mol / l. The concentration of ions after adding to 1 liter of solution 16,4h Na 3 PO 4 reduced in times. Task 2. Determine the solubility rational ovens usa product rational ovens usa of strontium carbonate, if its solubility at 25 C is 0,001554h / l. g / mol. Solution. Determine the solubility in mol / L mol / l. Strontium carbonate dissociates scheme. Based on the dissociation equation, we obtain a formula product solubility. Problem 3. Calculate the pH at which precipitation begins and ends cobalt rational ovens usa hydroxide solution of 0.1 M cobalt sulfate. . Solution. In solution dissociates scheme. Then the solubility product will be. Oskol