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MCAT

Unit 3: Lesson 1

Chemical and physical sciences practice passage questions

Alcohol production and absorption

Problem

Ethanol (CH3CH2OH) is a clear, colorless liquid with a distinct odor and is the alcohol found in alcoholic beverages. In addition to its other physical properties (Table 1), alcohol is flammable and volatile, lending it to be used as a solvent, an antiseptic, a fuel, in thermometers, and in other laboratory procedures. As a psychoactive substance, it is one of the most widely consumed recreational drugs by humans. It suppresses certain functions of the brain while causing the classic symptoms of intoxication including slurred speech, unsteady walk, and disturbed sensory perceptions.
Melting pointminus, 114, point, 1, degrees, C
Boiling point78, point, 5, degrees, C
Density0.79 g/mL
Molar mass46.07 g m, o, l, start superscript, minus, 1, end superscript
Table 1: Physical properties of ethanol at 20°C
Ethanol is produced by the fermentation of sugar. This process is catalyzed by zymase, an enzyme in yeast which changes simple sugars into ethanol and carbon dioxide. This fermentation reaction is represented by the equation in Figure 1.
C, start subscript, 6, end subscript, H, start subscript, 12, end subscript, O, start subscript, 6, end subscript ------> 2 C, H, start subscript, 3, end subscript, C, H, start subscript, 2, end subscript, O, H plus 2 C, O, start subscript, 2, end subscript
Figure 1. The alcohol fermentation reaction
Starches from potatoes, corn, wheat, and other plants can also be used to produce ethanol through fermentation. However, the starches must first be broken down. This is accomplished by enzymes, such as diastase, which converts starches into simple sugars. This step is typically associated with the brewing of beer from starchy plants such as corn and wheat.
After an alcoholic beverage is consumed, it passes through the stomach into the small intestine where the ethanol is absorbed and later distributed throughout the body. Ethanol is toxic, and the body begins to dispose of it upon its consumption. In the liver, the alcohol dehydrogenase enzyme converts ethanol into acetaldehyde. Acetaldehyde is later destroyed almost immediately by the aldehyde dehydrogenase enzyme.
Figure 2: The conversion of ethanol to acetaldehyde
What would be the volume of 1.58 moles of ethanol at 20°C?
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