PART II: PCAT DIAGNOSTIC TEST in Visual Studio .NET

Making DataMatrix in Visual Studio .NET PART II: PCAT DIAGNOSTIC TEST

9 Answer: B For a molecule to be polar, the molecule must have polar bonds and the bond vectors must not cancel out All the molecules have polar bonds, but the vectors cancel, except in PF3, which is trigonal pyramidal The VSEPR structures of the molecules (lone pairs except those on the central atom have been omitted) and the orientations of the bond vectors are shown below each structure

10 Answer: A Melting is the phase transition from solid to liquid The phase diagram with the regions labeled is shown below Only the transition from A B would include melting when the substance crosses the solid-liquid line

11 Answer: D The osmotic pressure ( ) for a solution is = MRT where M is the molarity of particles, R is the gas constant, and T is the Kelvin temperature CaCl2 is an ionic solid that separates into ions: CaCl2(aq) Ca2+(aq) + 2Cl (aq) For each mole of CaCl2 that dissolves, three moles of particles are formed A 050 M solution of CaCl2 will have a molarity of 15 M in particles The temperature must be converted to K (27 + 273 = 300 K) The osmotic pressure will be: = 15 mol L atm 0082 300 K = 369 atm L mol K

Choice A uses a molarity of 05 M Choice C uses the temperature in Celsius Choice B combines the errors in A and C 12 Answer: B The rate of a reaction can be increased by increasing the concentration of the reactants (which allows more collisions), by increasing the temperature (which increases the fraction of molecules with suf cient energy to react successfully), or by adding a catalyst (which lowers the activation energy of the reaction) Increasing the volume of the reaction will decrease the concentration of the reactants, which will slow the reaction rate 13 Answer: B The equilibrium constant is the product of the concentrations of the products raised to the power equal to the coef cients in the balanced equation divided by the product of the concentrations of the reactants raised to the power equal to the coef cients in the balanced equation Pure solids and liquids are left out of the expression This is why choices C and D are incorrect 14 Answer: A A substance will be more soluble in acidic solution if the anion reacts with the acid This will happen if the anion is a base that reacts with acids Hydroxide is a strong base, so sparingly soluble metal hydroxides are more soluble in acidic solutions The anions Cl and NO3 are the conjugate bases of the strong acids HCl and HNO3, respectively Conjugate base strength is inversely related to the acid from which the base is derived, so Cl and NO3 are very weak bases The weak acid CN has a relatively strong conjugate base CN which will react with acids according to the reaction below H+(aq) + CN (aq) HCN(aq) By removing the CN ion from solution, the solubility equilibrium shifts to the right allowing more Ni(CN)2 to dissolve 15 Answer: D The reactions given in the problem are reductions, so one must be reversed to be the oxidation of the reaction Reduction occurs at the cathode and oxidation occurs at the anode The problem states that Cd is the anode, so this reaction must be reversed If the reaction is reversed, the sign of E must also be reversed The cathode half reaction must be multiplied by 2 to balance the number of electrons transferred, but the E is not multiplied by this number Remember the V = J C, so multiplying charge also multiplies energy, but the ratio J C is still the same value The incorrect answers arise from not reversing the Cd half reaction, multiplying the Ni reaction E by 2, or a combination of these two errors Cd(s) + 2OH (aq) Cd(OH)2 (s) + 2e Eo = +081V Eo = +049V