Free Test Prep MCAT Exam Questions

Section: Physical Sciences 

TMS (tetramethylsilane) is commonly added to nuclear magnetic resonance (NMR) samples. It has a chemicalshift which is upfield of most organic signals, and it gives a strong, sharp singlet peak and can be easilyremoved. Why is TMS added to NMR samples?Section: Physical Sciences 

What is the relationship between suicide rates and social change according to the sociologist Emile Durkheim?Section: Psychology and Sociology 

Several techniques have been developed to determine the order of a reaction. The rate of a reaction cannot bepredicted on the basis of the overall equation, but can be predicted on the basis of the rate-determining step.For instance, the following reaction can be broken down into three steps.A + D → F + GStep 1A → B + C(slow)Step 2B + D → E + F(fast)Step 3E + C → G(fast)Reaction 1In this case, the first step in the reaction pathway is the rate-determining step. Therefore, the overall rate of thereaction must equal the rate of the first step, k1 [A] where k1 is the rate constant for the first step. (Rateconstants of the different steps are denoted by kx, where x is the step number.)In some cases, it is desirable to measure the rate of a reaction in relation to only one species. In a secondorder reaction, for instance, a large excess of one species is included in the reaction vessel. Since a relativelysmall amount of this large concentration is reacted, we assume that the concentration essentially remainsunchanged. Such a reaction is called a pseudo first-order reaction. A new rate constant, k', is established, equalto the product of the rate constant of the original reaction, k, and the concentration of the species in excess.This approach is often used to analyze enzyme activity.In some cases, the reaction rate may be dependent on the concentration of a short-lived intermediate. This canhappen if the rate-determining step is not the first step. In this case, the concentration of the intermediate mustbe derived from the equilibrium constant of the preceding step. For redox reactions, the equilibrium can becorrelated with the voltage produced by two half-cells by means of the Nernst equation. This equation statesthat at any given moment:Equation 1Whena A + b B → c C + d DReaction 2Note: R = 8.314 J/K·mol; F = 9.6485 × 104 C/mol.)Catalysts are effective in increasing the rate of a reaction because they:Section: Physical Sciences

In the course of gathering data in an experiment, a researcher develops the following correlation matrix:Table 1 Correlation MatrixWhich of the following pairs of variables are most strongly correlated?Section: Psychology and Sociology