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Final Exam Review

Final Exam Review. Quick Buffer/Titration Review. Problem areas on the exam. Steps for buffer problem with addition of acid or base. . Step 1: Decide if it is a buffer Step 2: Write reaction of buffer with strong acid or base

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Final Exam Review

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  1. Final Exam Review

  2. Quick Buffer/Titration Review Problem areas on the exam

  3. Steps for buffer problem with addition of acid or base. • Step 1: Decide if it is a buffer • Step 2: Write reaction of buffer with strong acid or base (a generic HA+OH- H20++A- or H++ A- HA+H2Ois fine) • Step 3: Find final amounts of each species (I suggest an ICF chart) to find amount of weak acid or base • Suggested, do this in mols • Step 4: Decide what type of solution you have and continue: • If weak acid or base use: ICE chart and Ka or Kbect…as we did with other equilibrium problems. • If using Ka or Kb equation use molarity • If both weak acid/base pair is present use HH equation • If using HH equation use moles

  4. Example Problem A 100.0 mL buffer solution has 0.150 M Na2HPO4 and 0.100 M KH2PO4. a) What is the pH of the buffer? b) What is the pH if 80.0 mL of 0.0100 M NaOH is added to the buffer solution?

  5. Walking Through Species Present: Lessons Learned from exam: Memorizing the order won’t help, learn what is happening at each point!!!! Atkins and Jones

  6. Kinetics Review

  7. Unique rates of Reaction: Example A) In the reaction 3ClO-(aq)2Cl-(aq)+ClO3-(aq), the rate of formation of Cl- is 3.6 M/min. What is the rate of reaction of ClO-? B) In the reaction 3ClO-(aq)2Cl-(aq)+ClO3-(aq), the rate of formation of Cl- is 3.6 M/min. What is the unique rate of the reaction? C) What is the rate of chromate ion consumption, when the rate of dichromate ion formation is 0.14 (M/s) in the following reaction: 2CrO42-(aq)+2H+Cr2O72-(aq)+H2O(l)

  8. Why would multiple steps matter? Slow Fast Gold Metallist Olympic Team! 4x100 36.84sec World record Don’t worry I will fill in!!! Oh no I have fallen ill! New time: 9.1+8.9+9.0+30= 59.0sec But that’s worse than most high school 4x100 times!!!! That can’t be right my hair is aerodynamic. If the slowest step is way slower than the others it’s the only one that matters.

  9. Why would multiple steps matter? Slow Fast Gold Metallist Olympic Team! 4x100 36.84sec World record Don’t worry we will fill in!!! Oh no we have fallen ill! New time: 9.1+0.5+0.6+0.4= 10.6sec If the slowest step is way slower than the others it’s the only one that matters. “slow” and “fast” are relative

  10. Why would multiple steps matter? • Why would multiple steps matter? • Write the rate law based on only slow reaction. • No intermediates allowed! For Example: Rate Rate 10 M/min 5 M/day 5 M/day Slow OR 1 M/hour 1 M/sec Fast Since no intermediates present: Done!!!! What if there are intermediates????

  11. Fast Slow • But what if your rate law does have an intermediate? • Remembering that at equilibrium a forward and reverse reaction are the same speed • Solve for the intermediate, in this case [C] • Fill into rate law

  12. Example Problems • A) NO reactions with hydrogen according to the following equation, the mechanism for the reaction involves the two steps shown below. What is the predicted rate law for the reaction? (hint: Be careful not to overcomplicate this one) • The following is a mechanism of Hydrogen and bromine reacting to form hydrogen bromide (HBr). First, write the overall reaction, then find the rate law of the reaction (remember that those two aren’t necessarily related).

  13. Catalysts vs. Intermediates vs. Transition States What is the Molecularity of each step? Step 1: Bimolecular step 2: Bimolecular Assuming that the first step is slow, what is the likely order of the reaction? Second Which is the intermediate? AB Which is the catalyst? A Which is the transition state? Trick Question

  14. Experimental Setup • Hold one concentration constant while varying the other • Then switch • Observe rates of reaction and draw conclusions about the exponents

  15. Summary: 0, 1st, 2nd order Kinetics = Given on the exam

  16. Integrated Rate Law Practice • Problem 4- • A) For a decomposition reaction that is first order, after how many seconds will 11.2% of the reactant remain when K = is 0.0140M/s-1 at 673 K.? • B) The half life for a second order reaction of a substance A is 50.5s when [A]o=0.84mol/L. Calculate the time needed for the concentration of A to decrease to 1/16, 1/4 and 1/5 its original value.

  17. Other Kinetic Examples: Use the following data to determine the rate law for the reaction between nitrogen oxide and chlorine to form nitrosyl chloride. Be sure to state what k is (including units). Problem 6- Find the activation energy of the reaction using the following graph of temperature vs. Keq?

  18. Collision Theory • In order to react molecules must collide: • What happens as you increase the number of collisions? • Reaction Rate increases. • How do we increase number of collisions? • Analogy: People in a room • Increase number of particles • Increase speed of particles: aka increase temperature

  19. Atkins Catalysis • Lowers activation energy • Not used up in the process. • Works through a variety of methods, 2 will be discussed here

  20. Molecularity vs. Order (Question 7) • Molecularity: Number of colliding entities in a step of a reaction • Unimolecular, Bimolecular, Termolecular • Order refers to the whole reaction, not a single step • Molecularity: Theoretical, based on collision theory • Order is an experimental concept: Based on overall rate law. C A B bimolecular C unimolecular D 7th order

  21. Question 8: Give three ways you can speed up a reaction, why do each of these work? • Raise the temperature- increases the energy of molecules collisions and increases the number of collisions • Increase the concentration- creates more collisions • Use a catalyst- lowers the activation energy

  22. Nuclear Chemistry Review

  23. Radioactive Decay Processessummary • A nuclei decays and becomes two particles or a particle and energy. • Spontaneous • Typically measured in half-life with bulk amounts • Impossible to estimate when one particle will decay • Follows first order kinetics • We’ll discuss 5 types.

  24. Usually restricted to heavier elements (Z=83+ typically) • Occurs when Proton:Neutron ratio is too large Alpha Decay Beta Decay • Occurs in proton deficient nuclei • Transforms neutrons into a proton, emits electron or beta particle • Nucleus “captures” a surrounding electron • Effectively turns proton into neutron. • Atomic number decreases by one. • Mass number doesn’t change Positron Decay • Occurs when neutron to proton ratio is too small • A proton turns into a neutron and a positron Gamma Emission • After α or β decay an excited nuclide is formed • Energy is released in form of photon in the γ portion of the EM spectrum • Normally fast but meta-stable compounds can be formed Electron Capture

  25. Examples

  26. Fission vs. Fusion • Fission • Nuclei split • Occurs spontaneously with Z=90+ • Typically will also eject some neutrons • Example • Fusion • Comines small nuclei into more stable large ones. • No radioactive waste • More energy • Example

  27. Atom Bomb vs. Hydrogen Bomb Atom Hydrogen • Detonated with conventional explosives which detonate atom bomb, setting off hydrogen bomb • Relies on fusion • More energy=more destruction • Less radioactive exposure • Never deployed in warfare • Detonated with conventional explosives • Relies on fission • Two deployed in warfare

  28. Nuclear Stability and Binding Energy

  29. Reaching Stability Band Nuclei in proton rich areas “ below” stability band, by emitting a positron, capturing an electron, or emitting a proton. Species “above” band are neutron rich, convert neutrons into protons by  emission

  30. Examples: Predicting Radio Active Decay • Predict whether the nuclei listed is more likely to undergo beta decay or positron emission. • Ge-66 (Ideal N/Z=1.18) • Actual N/Z= (66-32)/32=1.06 • b+ • Rh-105 (1.28) • Actual N/Z=(105-45)/45=1.33 • b-

  31. Einstein Mass-Energy Relationship Things to remember/common mistakes • Total mass of nuclei is always less than sum of components. • The difference in mass is the “mass defect” Mass defect is related to nuclear binding energy by ΔE=|Δm|c2 • Be sure to use kg as mass, do not use g/mol • For a more useful comparison amongst different nuclei, divide binding energy by the number of nucleons • Sig figs: • Remember: for mass defect you are doing +/- so you need to use decimal places • For the conversion and E=mc2 you are doing * and / so you need to use significant figures.

  32. Binding Energy and Stability • The binding energy is a measure of stability • To compare nuclei you must compare binding energy per nucleon. • Higher binding energy per nucleon is more stable. • Highest amongst intermediate masses, between 40-100 • 56Fe is most stable nuclei. Fission Fusion Is 2H more likely to undergo fusion or fission? Fusion Which nuclei is more stable 6Li or 110Cd? 110Cd Atkins

  33. Kinetics of Radioactive Decay • First order kinetics (only one reactant) • Recall: Rate=K*[A] • Aka: t=λN (t=rate at a time t, λ is the decay constant, N is number of radioactive nuclei at time t) • Written as the integrated rate law • ln(Nt/No)=-λt • Half life equation • t(1/2)= 0.693/λ

  34. Electrochemistry Review

  35. Balancing Redox Reaction Practice

  36. Definitions: Galvanic vs. Electrolytic Cells • Galvanic: Chemical energy into electric energy • Spontaneous: no battery needed • Electrolytic: Electric energy into chemical energy • Non-spontaneous: external power source needed.

  37. Determining Cell Reactions Determine the spontaneous cell reaction that occurs with Zn and Ni Determine the non-spontaneous cell reaction that occurs with Zn and Ag

  38. More Electrochemistry Practice D • A) A galvanic cell uses the half-cells Pb2+/Pb and Zn2+/Zn, and a salt bridge containing KCl(aq). What does the voltage meter read? • B) In the Daniell cell, the anode is zinc metal and the cathode is copper metal. When the cell operates, the anode mass ___________ and the cathode mass __________. • C) Write the proper cell diagram for the following reaction: (concentrations unknown and therefore no need to include them)2AuCl(s) + H2(g) 2Au(s) + 2H+(aq) + 2Cl-(aq) • D) In the cell shown above, A is a standard Zn2+/Zn electrode connected to a standard hydrogen electrode (SHE). If the voltmeter reading is -0.76 V, which half-reaction occurs in the left-hand cell compartment? • E) For the cell below there is a Zn/Zn2+ half cell and a Cu1+/Cu2+half cell with a KCl salt bridge. Label each letter with the chemical species present. E

  39. More about electrolytic cells • Reminder: Changes electrical power into chemical power (i.e., the reverse of the galvanic cell) • Power must be supplied • Anode and Cathode are usually in the same container and usually only contain one electrolyte. • Electrolyte can be molten or aqueous.

  40. Example: Sodium is produced by electrolysis of molten sodium chloride. What are the products at the anode and cathode, respectively? • How many moles of O2(g) are produced through electrolysis of a water solution that contains Na2SO4(aq) after applying an electric current of 0.120 A for 65.0 min? (Hint: the O2 is produced by the electrolysis of water 2H2O2H2+O2)

  41. Electroplating

  42. Example finding oxidation state: • A current of 15.0 A electroplated 50.0 g of hafnium metal from an aqueious solution in 2.00 H. What is the oxidation number of hafnium in the solution?

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