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Equilibrium 1994A Teddy Ku 1994 A • • MgF2(s) Mg2+(aq) + 2F-(aq) In a saturated solution of MgF2 at 18 degrees Celsius, the concentration of Mg2+ is 1.21x103 molar. The equilibrium is represented by the equation above. a) Write the expression for the solubility-product constant, Ksp, and calculate its value at 18 degrees Celsius. Ksp = [Mg2+] [F-]2 [F-] = 2(1.21x10-3) Ksp = (1.21x10-3)(2.42x10-3)2 = 7.09x10-9 1994 A • • b) MgF2(s) Mg2+(aq) + 2F-(aq) In a saturated solution of MgF2 at 18 degrees Celsius, the concentration of Mg2+ is 1.21x103 molar. The equilibrium is represented by the equation above. Calculate the equilibrium concentration of Mg2+ in 1.000 liter of saturated MgF2 solution at 18 degrees Celsius to which .100 mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible. MgF2(s) Mg2+(aq) + 2F-(aq) Initial (M) 0 Change (M) 0 -x Equilibrium (M) 0 1.21x10-3 - x 1.21x10-3 2.42x10-3 + .100 -2x 2.42x10-3 + .100 - 2x Kc = [Mg2+] [F-]2 = (1.21x10-3 - x)(2.42x10-3+.100 - 2x)2 = 7.09x10-9 Solve for x on calculator X= 1.20929x10-3 [Mg2+] = 1.21x10-3 + x = 2.42x10-3 • • c) • • • 1994 A MgF2(s) Mg2+ + 2F-(aq) In a saturated solution of MgF2 at 18 degrees Celsius, the concentration of Mg2+ is 1.21x103 molar. The equilibrium is represented by the equation above. Predict whether a precipitate of MgF2 will form when 100.0 milliliters of a 3.00x10-3 molar Mg(NO3)2 solution is mixed with 200.0 milliliters of a 2.00x10-3 molar NaF solution at 18 degrees Celsius. Calculations to support your prediction must be shown. Set up the equilibrium law and calculate (did in a) – Ksp=7.09x109 Calculate ion product – (3.00x10-3)(2.00x10-3)2=1.2x10-8 Compare ion product with Ksp – If the ion product > Ksp, the solution is supersaturated, and precipitate will form. – If the ion product is < or = to the Ksp, no precipitate will form. – 1.2x10-8 < 7.09x109 • No precipitate 1994 A • • MgF2(s) Mg2+ + 2F-(aq) In a saturated solution of MgF2 at 18 degrees Celsius, the concentration of Mg2+ is 1.21x103 molar. The equilibrium is represented by the equation above. At 27 degrees the concentration of Mg2+ in a saturated solution of MgF2 is 1.17x10-3 molar. Is the dissolving of MgF2 in water an endothermic or an exothermic process? Give an explanation to support your conclusion Equilibrium shifts to the left when temperature increases d) • – • Heat must be a product Exothermic if heat is a product