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Unformatted text preview: [ Print View ] General Chemistry II Assignment 5 Due at 11:00am on Tuesday, August 12, 2008 View Grading Details Common Ion Effect on Solubility Lead thiocyanate, , has a of . Part A Calculate the molar solubility of lead thiocyanate in pure water. The molar solubility is the maximum amount of lead thiocyanate the solution can hold. Part A.1 Identify the chemical equation Part not displayed Part A.2 Identify the expression Part not displayed Part A.3 Express in terms of the molar solubility Part not displayed Express the molar solubility numerically. ANSWER: 1.7110 2 Part B Calculate the molar solubility of lead thiocyanate in 0.900 . Part B.1 Express in terms of the molar solubility Part not displayed Part B.2 Simplify the expression Part not displayed Express the molar solubility numerically. ANSWER: 2.4710 5 Effect of pH on Solubility Different salts have different solubilities in water. For some salts, the addition of or to the solution can actually increase its solubility. Part A , , and are all sparingly soluble salts. Which of these salts will be more soluble in an acidic solution than in water? Hint A.1 How to approach the problem Hint not displayed Part A.2 Describe the anion of AgI Part not displayed Part A.3 Describe the anion of BaF 2 Part not displayed Part A.4 Describe the anion of AgBr Part not displayed ANSWER: is the correct answer. The addition of ions (from a strong acid such as is useful to aid the solubility of because the ions react with the ions to form the weak acid . Because is a weak acid, it has a relatively small . In other words, the equilibrium of the dissociation reaction lies to the left. Thus the ions are effectively removed from solution, since they form with the ions. This pulls the equilibrium of the dissociation reaction of the sparingly soluble salt, to the right, increasing the solubility of . Part B As a chemist for an agricultural products company, you have just developed a new herbicide,"Herbigon," that you think has the potential to kill weeds effectively. A sparingly soluble salt, Herbigon is dissolved in 1 acetic acid for technical reasons having to do with its production. You have determined that the solubility product of Herbigon is 9.2010 6 . Although the formula of this new chemical is a trade secret, it can be revealed that the formula for Herbigon is X- acetate ( , where "X" represents the top-secret cation of the salt). It is this cation that kills weeds. Since it is critical to have Herbigon dissolved (it won't kill weeds as a suspension), you are working on adjusting the pH so Herbigon will be soluble at the concentration needed to kill weeds. What pH must the solution have to yield a solution in which the concentration of is 4.5010 3 ? The of acetic acid is 4.76....
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