This time the concentration of the chloride ions is governed by the concentration of the sodium chloride solution. The calculations are different from before. As before, define s to be the concentration of the lead II ions. If an attempt is made to dissolve some lead II chloride in some 0. This type of response occurs with any sparingly soluble substance: it is less soluble in a solution which contains any ion which it has in common. The lead II chloride becomes even less solubleand the concentration of lead II ions in the solution decreases. Of course, the concentration of lead II ions in the solution is so small that only a tiny proportion of the extra chloride ions can be converted into solid lead II chloride. What happens to that equilibrium if extra chloride ions are added? The chloride ion is common to both of them this is the origin of the term "common ion effect". Sodium chloride shares an ion with lead II chloride. Consider what happens if sodium chloride is added to this saturated solution. Consider the lead II ion concentration in this saturated solution of PbCl 2. John poured If a common ion is added to a weak acid or weak base equilibrium, then the equilibrium will shift towards the reactants, in this case the weak acid or base. The following examples show how the concentration of the common ion is calculated. Consideration of charge balance or mass balance or both leads to the same conclusion. For example, a solution containing sodium chloride and potassium chloride will have the following relationship. Contributions from all salts must be included in the calculation of concentration of the common ion. If the salts contain a common cation or anion, these salts contribute to the concentration of the common ion. If several salts are present in a system, they all ionize in the solution. The solubility products K sp 's are equilibrium constants in hetergeneous equilibria i. The Bohr Model.The common-ion effect is used to describe the effect on an equilibrium involving a substance that adds an ion that is a part of the equilibrium. Stoichiometric Calculations: Amounts of Reactants and Products. Calculations Involving a Limiting Reactant.Ĭhemical Equations and Balancing Chemical Equations. Potential inside a non conducting solid sphereĪP Chemistry.
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