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CEGEP • Montreal

Chemistry of Solutions, 202-SN2-RE (formerly 202-NYB)

Chemistry of Solutions, 202-SN2-RE in the revised program (formerly 202-NYB), revolves almost entirely around a single idea, chemical equilibrium, applied in turn to acids and bases, to solubility and to redox reactions. A student who has truly mastered the ICE table gets through the term without trouble.

9 fully corrected exercise sets (102 exercises), 9 revision sheets, and a practice paper. Free, no account needed. The same course in French.

Measurement and reaction rates

  1. 1 Measurement, uncertainty and graphical analysis The chemistry of solutions laboratory, where the constant you are after is no longer a reading but a slope. Tolerances of volumetric glassware and the accumulation of uncertainties in a serial dilution, a Beer-Lambert calibration curve calculated by hand by least squares, the coefficient of determination and what it does not say, the uncertainty on the slope by the extreme-lines method, reading an unknown concentration backwards and the range of linearity. Then an exam-level part: the plot that decides between first and second order, the passage through a logarithm that turns a hundredth of a pH unit into five percent on a concentration, the exponent that triples a relative uncertainty in a solubility product, an iron tablet assayed by spectrophotometry with its uncertainty budget and its waste, and an activation energy read from an Arrhenius slope. Sheet
  2. 2 Chemical kinetics Average rates and stoichiometric ratios, the method of initial rates with the units of k to justify, the three integrated rate laws told apart by the behaviour of their successive half-lives, the Arrhenius equation and activation energy. Then an exam-level part: the energy profile that shows why a catalyst lowers both barriers by the same amount and so cannot shift the equilibrium, a pre-equilibrium mechanism whose intermediate must be eliminated and which explains a negative apparent activation energy, a mechanism tested against the experimental rate law, drug elimination and the industrial choice between heating and catalyzing. Sheet

Equilibrium, acids and bases

  1. 3 Chemical equilibrium Writing an equilibrium constant and predicting a direction with the reaction quotient, manipulating Kc (reversing, halving, combining equations), the ICE table with the 5% test and then the full quadratic, the relation Kp = Kc(RT) to the power delta n with the wrong-R trap, and heterogeneous equilibria where solids drop out of the expression. Then an exam-level part: the degree of dissociation that changes with dilution while the constant does not move, the three Le Chatelier traps (inert gas at constant volume, then at constant pressure, and a catalyst) settled by calculating Q rather than by reciting a rule, a perfect square that avoids the quadratic, and the van 't Hoff relation used to work back to the enthalpy. Sheet
  2. 4 Acids and bases The pH scale and strong solutions, Brønsted conjugate pairs and the favoured direction, the weak acid whose percent ionization rises on dilution, the weak base and the Ka times Kb relation, and polyprotic acids, where the carbonate ion concentration is shown to equal Ka2 numerically, whatever the dilution. Then an exam-level part: the strong acid-strong base titration point by point, the weak-acid titration with its four regions, including the half-equivalence point that gives the pKa by simple reading, the four cases of salt hydrolysis, a buffer compared with pure water, and the preparation of a buffer pushed until its capacity breaks down. Sheet
  3. 5 Titrations and buffer solutions A titration curve read for four pieces of information, including the pKa that is read directly at the half-equivalence point, the titration of a weak base by a strong acid where the equivalence point falls on the acidic side, the diprotic acid and its two unequal jumps, the buffer index worked out and compared with its theoretical maximum, and the dilution that leaves the pH unchanged but divides the robustness by ten. Then an exam-level part: the titration error worked out at minus sixty-nine percent when the wrong indicator is chosen, the first derivative method, five statements to correct, the back titration of an antacid tablet, and the bicarbonate buffer of blood with its acidosis and its respiratory compensation. Sheet

Solubility and electrochemistry

  1. 6 Solubility and the solubility product Going from Ksp to molar solubility for three stoichiometries and making the reverse trip from a solubility measured in grams per litre, the common-ion effect justified by Le Chatelier, the ion product that decides whether a precipitate will form, and selective precipitation. Then an exam-level part: complex ions that make silver chloride four thousand times more soluble in ammonia yet leave the iodide untouched, amphoteric hydroxides with the calculation of the pH of minimum solubility, the solubility of hydroxides as a function of pH, the softening of hard water and a gravimetric analysis in which the washing error is put in numbers. Sheet
  2. 7 Redox and electrochemistry Oxidation numbers and their two exceptions, balancing by half-reactions in acidic and then basic solution, the galvanic cell with its salt bridge, the three ways of writing the same information (E°, ΔG° and K), the Nernst equation and the concentration cell, Faraday's laws, and predicting the products of an aqueous electrolysis, where water sets the limit. Then an exam-level part: the titration of iron with permanganate, corrosion and cathodic protection with the sizing of a sacrificial anode, and the lead-acid battery compared with gasoline in energy density. Sheet

Thermodynamics and solutions

  1. 8 Chemical thermodynamics The enthalpy of reaction from enthalpies of formation, Hess's law to reach an enthalpy that no calorimeter can measure, the predictable sign of the entropy change, Gibbs free energy and its four cases, and the crossover temperature read off a straight line. Then an exam-level part: the entropy of the universe, which shows that the criterion delta G below zero is just the second law rewritten, the step from delta G to the equilibrium constant, the calculation away from standard conditions that explains why a swept lime kiln works well below its crossover temperature, the Haber process and the reduction of a metal oxide by carbon. Sheet
  2. 9 Solutions and colligative properties The chapter on solutions revisited with the tools of the second course: dissolution becomes an equilibrium that can be put in numbers. The enthalpy of solution from the lattice-versus-hydration cycle, the entropy that makes a dissolution that cools spontaneous, Henry's law treated as an equilibrium constant and run through van 't Hoff on the oxygen of a warmed river, the Ka of a weak acid recovered by freezing-point depression and the reason the method is worthless, ionic strength and the activity coefficients that explain the salt effect. Then colligative properties read off the phase diagram, deviations from Raoult's law and azeotropes, five statements to correct, freeze-drying from the triple point to the energy balance, and liquid-liquid extraction, where splitting the solvent divides the loss by ten. Sheet

When the chapters are done

A full paper under exam conditions, on the whole course. Do it once every chapter is behind you: it measures what you can do on a question you have never seen.

Practice exam

Practice final exam, 202-SN2-RE

A full final-exam paper: 12 exercises in 3 hours, marked out of 100, with a detailed solution for every question. Each exercise crosses several chapters and no question announces its method. An equilibrium constant read from the ratio of rate constants, the activation energies of the two directions tied to the enthalpy, sulfides precipitated under pH control, a selective separation by a buffer, the choice of a colour indicator, a standard potential deduced from a solubility product, a fuel cell compared with Carnot efficiency, and an unknown species identified from four measurements.

  • 12 questions
  • 100 points
  • 180 minutes
Sit the paper

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