If NaOH is added slowly, what compound would precipitate first? The two equations I wrote were. Is this correct? If the question is about what compound would precipitate first, then there can be at most one answer.
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See all problems in Ksp. Frequently Asked Questions What scientific concept do you need to know in order to solve this problem? What is the difficulty of this problem? How long does this problem take to solve? What professor is this problem relevant for? Log in with Facebook. From that, we calculate the pH. At equilibrium:. If the person doing laundry adds a base, such as the sodium silicate Na 4 SiO 4 in some detergents, to the wash water until the pH is raised to Due to their light sensitivity, mixtures of silver halides are used in fiber optics for medical lasers, in photochromic eyeglass lenses glass lenses that automatically darken when exposed to sunlight , and—before the advent of digital photography—in photographic film.
When two anions form slightly soluble compounds with the same cation, or when two cations form slightly soluble compounds with the same anion, the less soluble compound usually, the compound with the smaller K sp generally precipitates first when we add a precipitating agent to a solution containing both anions or both cations.
When the K sp values of the two compounds differ by two orders of magnitude or more e. This is an example of selective precipitation , where a reagent is added to a solution of dissolved ions causing one of the ions to precipitate out before the rest. Solubility equilibria are useful tools in the treatment of wastewater carried out in facilities that may treat the municipal water in your city or town Figure 5.
Specifically, selective precipitation is used to remove contaminants from wastewater before it is released back into natural bodies of water. An abundance of phosphate causes excess algae to grow, which impacts the amount of oxygen available for marine life as well as making water unsuitable for human consumption. One common way to remove phosphates from water is by the addition of calcium hydroxide, known as lime, Ca OH 2.
The lime is converted into calcium carbonate, a strong base, in the water. As the water is made more basic, the calcium ions react with phosphate ions to produce hydroxylapatite, Ca 5 PO4 3 OH , which then precipitates out of the solution:.
The precipitate is then removed by filtration and the water is brought back to a neutral pH by the addition of CO 2 in a recarbonation process. Other chemicals can also be used for the removal of phosphates by precipitation, including iron III chloride and aluminum sulfate. View this site for more information on how phosphorus is removed from wastewater. Selective precipitation can also be used in qualitative analysis.
In this method, reagents are added to an unknown chemical mixture in order to induce precipitation. Certain reagents cause specific ions to precipitate out; therefore, the addition of the reagent can be used to determine whether the ion is present in the solution. View this simulation to study the process of salts dissolving and forming saturated solutions and precipitates for specific compounds, or compounds for which you select the charges on the ions and the K sp.
Precipitation of Silver Halides A solution contains 0. AgNO 3 is gradually added to this solution. Which forms first, solid AgI or solid AgCl? If the solution contained about equal concentrations of Cl — and I — , then the silver salt with the smallest K sp AgI would precipitate first.
Check Your Learning If silver nitrate solution is added to a solution which is 0. As we saw when we discussed buffer solutions, the hydronium ion concentration of an aqueous solution of acetic acid decreases when the strong electrolyte sodium acetate, NaCH 3 CO 2 , is added. Because sodium acetate and acetic acid have the acetate ion in common, the influence on the equilibrium is called the common ion effect.
The common ion effect can also have a direct effect on solubility equilibria. Suppose we are looking at the reaction where silver iodide is dissolved:.
If we were to add potassium iodide KI to this solution, we would be adding a substance that shares a common ion with silver iodide. In this example, there would be an excess of iodide ions, so the reaction would shift toward the left, causing more silver iodide to precipitate out of solution. View this simulation to see how the common ion effect work with different concentrations of salts.
The K sp of CdS is 1. Solution The first thing you should notice is that the cadmium sulfide is dissolved in a solution that contains cadmium ions. We need to use an ICE table to set up this problem and include the CdBr 2 concentration as a contributor of cadmium ions:. We can solve this equation using the quadratic formula, but we can also make an assumption to make this calculation much simpler. Since the K sp value is so small compared with the cadmium concentration, we can assume that the change between the initial concentration and the equilibrium concentration is negligible, so that 0.
Going back to our K sp expression, we would now get:. Therefore, the molar solubility of CdS in this solution is 1. The equilibrium constant for an equilibrium involving the precipitation or dissolution of a slightly soluble ionic solid is called the solubility product, K sp , of the solid.
The solubility product of a slightly soluble electrolyte can be calculated from its solubility; conversely, its solubility can be calculated from its K sp , provided the only significant reaction that occurs when the solid dissolves is the formation of its ions.
A slightly soluble electrolyte begins to precipitate when the magnitude of the reaction quotient for the dissolution reaction exceeds the magnitude of the solubility product. Precipitation continues until the reaction quotient equals the solubility product. A reagent can be added to a solution of ions to allow one ion to selectively precipitate out of solution.
The common ion effect can also play a role in precipitation reactions. Sea water has a density of 1. What mass, in kilograms, of Ca OH 2 is required to precipitate Find the K sp.
There is no change. A solid has an activity of 1 whether there is a little or a lot. The solubility of silver bromide at the new temperature must be known. The reaction quotient is also called the ion product when it is calculated using concentrations of species involved in solubility equilibria. One first calculates Q , then compares it with K sp. Note that precipitation may not happen immediately if Q is equal to or greater than K sp.
A solution could be supersaturated for some time until precipitation occurs. Fractional precipitation is a technique that separates ions from solution based on their different solubilities. Suppose that an aqueous solution of potassium chromate K 2 CrO 4 is added slowly. Two precipitates can form: BaCrO 4 with K sp of 1. Since all potassium salts are soluble, the potassium ion of the aqueous solution of K 2 CrO 4 is a spectator ion and does not need to be considered in the solubility equilibrium.
If one of the ions appearing in a solubility equilibrium is the conjugate base of a weak acid , then pH can affect the concentrations of ions in the solubility equilibrium. The magnitude of this effect can be estimated from the solubility product. Example: Consider two slightly soluble salts, calcium carbonate and calcium sulfate. Which of these would have its solubility more affected by the addition of HCl, a strong acid?
Would the solubility of the salt increase or decrease?. A strong acid affects the solubility of a salt of a weak acid by providing hydronium ion that reacts with the anion of the salt in the solution.
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