ap10_chemistry_scoring_guidelines - AP Chemistry 2010...

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AP ® Chemistry 2010 Scoring Guidelines The College Board The College Board is a not-for-profit membership association whose mission is to connect students to college success and opportunity. Founded in 1900, the College Board is composed of more than 5,700 schools, colleges, universities and other educational organizations. Each year, the College Board serves seven million students and their parents, 23,000 high schools, and 3,800 colleges through major programs and services in college readiness, college admission, guidance, assessment, financial aid and enrollment. Among its widely recognized programs are the SAT ® , the PSAT/NMSQT ® , the Advanced Placement Program ® (AP ® ), SpringBoard ® and ACCUPLACER ® . The College Board is committed to the principles of excellence and equity, and that commitment is embodied in all of its programs, services, activities and concerns. © 2010 The College Board. College Board, ACCUPLACER, Advanced Placement Program, AP, AP Central, SAT, SpringBoard and the acorn logo are registered trademarks of the College Board. Admitted Class Evaluation Service is a trademark owned by the College Board. PSAT/NMSQT is a registered trademark of the College Board and National Merit Scholarship Corporation. All other products and services may be trademarks of their respective owners. Permission to use copyrighted College Board materials may be requested online at: www.collegeboard.com/inquiry/cbpermit.html. Visit the College Board on the Web: www.collegeboard.com. AP Central is the official online home for the AP Program: apcentral.collegeboard.com.
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AP ® CHEMISTRY 2010 SCORING GUIDELINES Question 1 (10 points) Several reactions are carried out using AgBr, a cream-colored silver salt for which the value of the solubility- product-constant, K sp , is 5.0 × 10 13 at 298 K. (a) Write the expression for the solubility-product constant, K sp , of AgBr. K sp = [Ag + ][Br ] One point is earned for the correct expression (ion charges must be present; parentheses instead of square brackets not accepted). (b) Calculate the value of [Ag + ] in 50.0 mL of a saturated solution of AgBr at 298 K. Let x = equilibrium concentration of Ag + (and of Br ). Then K sp = 5.0 × 10 13 = x 2 x = 7.1 × 10 7 M One point is earned for the correct value with supporting work (units not necessary). (c) A 50.0 mL sample of distilled water is added to the solution described in part (b), which is in a beaker with some solid AgBr at the bottom. The solution is stirred and equilibrium is reestablished. Some solid AgBr remains in the beaker. Is the value of [Ag + ] greater than, less than, or equal to the value you calculated in part (b) ? Justify your answer. The value of [Ag + ] after addition of distilled water is equal to the value in part (b). The concentration of ions in solution in equilibrium with a solid does not depend on the volume of the solution.
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