This is because Le Chateliers principle states the reaction will shift toward the left (toward the reactants) to relieve the stress of the excess product.
![]() In the water treatment process, sodium carbonate salt is added to precipitate the calcium carbonate. The very pure and finely divided precipitate of calcium carbonate that is generated is used in the manufacture of toothpaste. Fluoride is more effective than calcium as a common ion because it has a second-power effect on the solubility equilibrium. ![]() Adding an additional amount of one of the ions of the salt generally leads to increased precipitation of the salt, which reduces the concentration of both ions of the salt until the solubility equilibrium is reached. The effect is based on the fact that both the original salt and the other added chemical have one ion in common with each other. There exists an equilibrium between unionized molecules and the ions in an aqueous medium as follows. Due to the increase in concentration of H ions, the equilibrium of dissociation of H 2 S shifts to the left and keeps the value of K a constant. As a result, the concentration of sulphide ions is decreased. The solubility is therefore reduced to 1.40 x 10 4 M, about five times smaller. ![]() The very pure and finely divided precipitate of calcium carbonate that is generated is a valuable by-product used in the manufacture of toothpaste. Addition of sodium chloride reduces the solubility of the soap salts. The soaps precipitate due to a combination of common-ion effect and increased ionic strength. In the presence of excess Na, the solubility of soap salts is reduced, making the soap less effective. For example, if both sodium acetate and acetic acid are dissolved in the same solution they both dissociate and ionize to produce acetate ions. Sodium acetate is a strong electrolyte, so it dissociates completely in solution. According to Le Chateliers principle, the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its equilibrium to the left. Thus the percent dissociation of the acetic acid will decrease, and the pH of the solution will increase. The ionization of an acid or a base is limited by the presence of its conjugate base or acid. For example, copper(I) chloride is insoluble in water, but it dissolves when chloride ions are added, such as when hydrochloric acid is added. This salting in is called the uncommon-ion effect (also salt effect or the diverse-ion effect). It occurs because as the total ion concentration increases, inter-ion attraction within the solution can become an important factor. This alternate equilibrium makes the ions less available for the precipitation reaction. Water Quality: An Introduction. Springer. pp. 56. ISBN 978-3-319-17446-4. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
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