1._____________ refers to the method by which an optically reactive reagent or catalyst is used to transform an optically inactive starting material into an optically active product. A. Racemization B. Enantioenrichment C. Chiral chromatography D. Asymmetric induction Correct Answer: D. Asymmetric induction Racemization refers to the conversion of an optically active substance to a racemic form (has equal amounts of left- and right-handed enantiomers of a chiral molecule). Enantioenrichment refers to the act of enriching an already existing mixture of stereoisomers such that it contains more than 50% of one enantiomer. Chiral chromatography involves the separation of stereoisomers using a chiral stationary phase, which does not involve chemical transformations. “Optical reduction” as a technique or phrase does not exist. -------------------------------------- 2.A liquid that has stronger cohesive forces than adhesive forces would have which type of meniscus? A. flat B. concave C. convex D. parabolic Correct Answer: C. convex. The meniscus is the curved upper surface of liquid. This is formed because of unequal cohesion and adhesion attractions. For example, in water the adhesive forces are greater than the cohesive forces, therefore the water is able to “walk up the sides” of the surface. In the case of water, a U-shaped or concave meniscus is formed. Mercury, for example has stronger cohesive attractions between the mercury molecules than adhesive attractions between the mercury and the glass surface, therefore producing a convex meniscus, which looks like an inverted U. -------------------------------------- 3.Which expression gives the acceleration of a 1kg mass on a frictionless inclined plane at 30o to the horizon, given that g = 9.8 m/s2? A. a = 9.8 m/s2 B. a = cos 30o x 9.8 m/s2 = 8.5 m/s2 C. a = sin 30o x 9.8 m/s2 = 4.9 m/s2 D. a = tan 30o x 9.8 m/s2 = 5.7 m/s2 Correct Answer: C. a = sin 30o x 9.8 m/s2 = 4.9 m/s2 Gravity is calculated from the vertical component of the force on the mass: sin theta = opposite/hypotenuse. -------------------------------------- 4.Which of the following should be observed with the addition of a catalyst to a chemical reaction? A. the formation of a new product B. the consumption of the catalyst C. the activation energy is lowered D. the decrease in enthalpy Correct Answer: C. the activation energy is lowered A catalyst speeds up a chemical reaction by lowering the activation energy of a reaction. The catalyst is never consumed, nor does it alter the reactants or products. The total enthalpy of the reaction is also not changed from what it would have been without the catalyst. Only the rate at which the reaction occurs and the activation energy is affected. The only answer option that is correct is [C]. -------------------------------------- 5.Enzymes are one of the key proteins in cells and facilitate chemical reactions. How does a typical enzyme catalyze a chemical reaction? A. It eliminates the activation energy of a chemical reaction B. It reduces the activation energy of a chemical reaction C. It provides additional energy to the chemical reaction D. It contains a covalently bound substrate, which is needed for the chemical reaction Correct Answer: B. It reduces activation energy of a chemical reaction Enzymes reduce the activation energy of chemical reactions by binding substrate(s) into energetically favorable orientations. They greatly reduce the activation energy, but do not eliminate it completely. Enzymes are completely reusable—they do not participate in the reaction as a substrate. Even when cofactors are needed for the successful action of the enzyme and though they may be tightly bound, they are not covalently bound to the enzyme. Enzymes do not add additional energy to chemical reactions as heat would.
Posted on: Fri, 25 Jul 2014 10:19:41 +0000
Trending Topics
Recently Viewed Topics
© 2015