Re-Cap of Gen Chem III

Hey everyone!

Your Required Homework before Verbal Reasoning III is as follows:

• Chapter 9, question 2 in Writing Sample Review Notes
• Critical Reading Challenge Workshop & Quiz
• Argument Dissection Challenge Workshop & Quiz

For those of you who would like some additional Verbal Reasoning review before class, I recommend the following:

• Verbal Reasoning Foundation Review Unit 3

Moving on, let’s discuss the review assignments for Gen Chem III:

• Acids & Bases Test 1
• Electrochemistry Test 1
  • Both of these topical tests serve as a nice recap on the concepts we discussed in the lesson.  There are a few questions that get carried away with the math, but the exams get the job done: they serve as a nice test on all the general chemistry you need to know for the exam.

Content Note:  A real-world application of redox reactions is demonstrated in this “explosive” YouTube video.  A violent redox reaction occurs when you put an alkali metal and water together as electrons are transferred from the metal to water.  Alkali metals are potent reducing agents, and this comes at no surprise given the low ionization energy of metals.  The other reactant, water, is the oxidizing agent as the hydrogen in water (+1 oxidation state) gets reduced to hydrogen gas (0 oxidation state).  So why the explosion?  When H₂ and O₂ hook up we get a combustion reaction, and there’s plenty of O₂ in the atmosphere.  (Side note: the glass shatters because the product of the redox reaction, CsOH, is a strong enough base to etch glass).  So this one tiny 25-second video combines concepts we discussed in Gen Chem I (ionization energy), Gen Chem II (combustion reactions), and Gen Chem III (redox reactions)!      

Helpful Hints:

• Now that we are in the 3^rd Unit of the Kaplan MCAT course, our focus is on integration of all our methods and strategies in the context of timed sections.  From this point on, make sure that you complete all Section Tests and Full Length Practice Tests under timed conditions.  In addition to practicing your pacing, you must work on building stamina and focus in anticipation of Test Day.
• The Gen Chem III lesson applies many of the same concepts we discussed in Gen Chem II.  Remember that the dissociation constant of an acid or base (K_a and K_b, respectively) is a measure of the equilibrium position in the same way that K_eq and K_sp are.
• Concentration cells are like voltaic (galvanic) cells in that they house a spontaneous redox reaction which releases energy.  Unlike voltaic cells, however, concentration cells have a standard EMF of 0 V because the redox reaction is “motivated” not by a difference in reduction potentials between two chemically different electrodes but rather by a concentration gradient of an ionic species (e.g. the proton-motive force across the inner mitochondrial membrane – the mitochondrion IS a concentration cell/battery!)

Also, here’s an interesting link.

• The Big Picture: fascinating pictures from the world of microscopy.  Those of you who like picture books may enjoy this blog, because all they do is post big pictures with scant explanation.