My Heart Rate When...

The first panel is funny because it is impossible to finish one free response question, let alone three, with only four seconds left in class. The graph is a normal heart rate graph, but the BPM is very high (normal human heart rate is about 60-100 BPM, according to the Mayo Clinic).

The second panel is a reference to a reaction approaching the equilibrium rate. As the reactants are used up, the rate of the forward reaction decreases and the rate of the reverse reaction increases. Because the rate is proportional to the square of the concentration of one reactant, this is a second order reaction (Rate = k[A]^2). When there is less of this reactant present, there is less chance of molecules colliding in the appropriate way to cause the reaction, and the reaction occurs at a slower rate. The BPM may represent the rate constant, k.

The third panel is a reference to titrations with various strengths of base (in this case; if the experiment involved a weak base instead of a weak acid, it would be titrated with acid). The equilibrium point occurs at the same place each time (the ~vertical line where all the lines converge on the graph) because the same amount of H+ and OH- ions react each time, no matter the concentration of the (in this case) base added because the weak acid/base will dissociate more (and eventually completely dissociate) to react with the H+ or OH- ions in solution, shifting the equilibrium Towards the dissociated product that is Taken by the neutralization reaction to form water, according to Le Chatelier's Principle. The Ka value defines how much of a weak acid/base dissociates. Half equivalence is the point where half of the amount of acid/base that will react has done so. Half of the titrant needed to reach the equilibrium point has been added. Also, [A-] = [HA] (the concentration of conjugate base is equal to the concentration of undissociated acid), making the pH of the solution equal to the pKa (because of the Henderson-Hasselbalch equation of awesomeness). As pKa = -log(Ka), the pH at half equivalence can allow an experimenter to determine the Ka value, as the mural asks. The BPM may represent the pH and pKa value. especially because it is specified as being at half equivalence and helps in determining the Ka value.