Pressure - MCAT Chemical and Physical Foundations of Biological Systems

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Question

Ethanol has a specific gravity of 0.780. If a long barometer tube is placed in a dish of ethanol, with the top end open to the atmosphere, to what height in the tube will the ethanol rise?

Atmospheric pressure = 1.01 * 105 Pa

g = 9.81 m/s2

Density of water = 1000 kg/m3)

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Answer

The pressure exerted by the air on the top of the ethanol must equal the fluid pressure in the column of liquid at equilibrium. Fluid pressure is the product of density, gravity, and height of the fluid.

The density of ethanol, , may be calculated by multiplying specific gravity times the reference density of water, as specific gravity is simply a ratio of a compound's density to that of water.

Using this density in the pressure equation allows us to solve for the height of the ethanol.

1.01 * $10^{5}$ Pa = left ( $780$\frac{kg}{m^{3}$$} right )left ( $9.81$\frac{m}{s^{2}$$} right )h

After calculating, h = 13.2 m

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