CH 102 1st Edition Lecture 18Outline of Current Lecture I. Preparation of a Tris BufferII. Titration of bicarbonate ion with strong acidIII. Titration Curve for Piperazine and HClIV. ThermodynamicsV. EntropyVI. Changes in EntropyVII. CrystallizationVIII. Gibbs Free EnergyCurrent LectureI. Preparation of a Tris Buffera. In the study of biochemical processes, a common buffering agent is the weak base trishydroxymethylaminomethane, (HOCH2)3CNH2, often abbreviated as Tris. At 25 ∘C, Tris has a pKb of 5.91.The hydrochloride of Tris is (HOCH2)3CNH3Cl, which can be abbreviated as TrisHCl.i. What volume of 10.0 M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of TrisHCl?1. pH = pKa + log [conjugate base]/[acid]II. Titration of bicarbonate ion with strong acida. Carbonic acid (H2CO3) is a weak diprotic acid with Ka1=4.43×10−7 and Ka2=4.73×10−11. The bicarbonate ion, HCO3−, reacts with the acid as shown in the equationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. HCO3- (aq) + H3O+ (aq) → H2CO3 (aq) + H2Ob. Salts of the bicarbonate ion, such as sodium bicarbonate (NaHCO3) act as weak bases. i. A 10.0-mL sample of 1.0 M NaHCO3 is titrated with 1.0 M HCl (hydrochloric acid). Approximate the titration curve by plotting the following points: 1. pH after 0 mL HCl added,2. pH after 1.0 mL HCl added,3. pH after 9.5 mL HCl added,4. pH after 10.0 mL HCl added (equivalence point),5. pH after 10.5 mL HCl added, and6. pH after 12.0 mL HCl added.III. Titration Curve for Piperazine and HCla. Piperazine, HN(C4H8)NH, is a diprotic weak base used as a corrosion inhibitor and an insecticide and has the following properties: i. pKb1=4.22ii. pKb2=8.67 b. For writing the reactions of this base in water, it can be helpful to abbreviate the formula as Pip: i. Pip + H2O D HPip+ + OH-ii. HPip+ + H2O D H2Pip2+ + OH-c. The piperazine used commercially is a hexahydrate with the formula C4H10N2⋅6H2O.IV. Thermodynamicsa. Thermodynamics determines whether a process is spontaneousb. Thermodynamics drives a process toward equilibriumc. Kinetics determines how fast.d. The process may be physical, e.g. melting, evaporation, expansion of a gase. The process may be chemicalf. Thermodynamics introduces two new state functionsi. Entropy -Sii. Gibbs free energy -GV. Entropya. Entropy is a thermodynamic function that increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular statei. S = k·logW1. Where:a. K is the Boltzmann constantb. W is the number of energetically equivalent statesb. For the complex systems we encounter, it is difficult, if not impossible, to determine Sc. We are more concerned with the change in entropy, ΔS.VI. Changes in Entropya. Entropy is a measure of the amount of disorder in a system b. S is a measure of the change in disorder for a process.c. Consider meltingd. The initial state is a crystalline substance, where the atoms (or molecules) are sitting in their lattice positions. This state has a low entropy.e. The final state is a liquid with the atoms (or molecules) moving from place to place with no positional order. This state has a higher entropy.VII. Crystallizationa. Crystallization of sugarb. A saturated solution of sucrose in water at high temperaturei. The initial state consists for water molecules and sucrose molecules in close contact, randomly moving through the liquidc. The solution is slowly cooled until the sucrose begins to crystallizei. Sucrose molecules moving around the solution collide with other sucrose molecules and stick together forming nuclei – the tiniest of sugar crystals (nanometers in size)ii. More sucrose molecules collide with the nuclei and are added to the surface of the crystal, thus growing the crystal.d. The solution is cooled until almost all the sucrose has crystallizedi. The system consist of highly crystalline sucrose and a very dilute solution of sucrose in waterii. Pure solvents have a lower entropy than solutionsiii. Crystals have a low entropye. For this process ΔS < 0VIII. Gibbs Free Energya. ΔG = ΔH – TΔS : Determines whether a process is spontaneousb. If ΔG < 0i. The process is spontaneous in the forward directionc. If ΔG > 0i. The process is not spontaneous in the forward directionii. It will be spontaneous in the reverse