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In a multi-liquid barometer, the following liquids are present in a column along with trapped gases NH3 and He (temperature = 300 K, atmospheric pressure = 1 atm). Liquid-1: height h1 = 19 cm, density d1 = 27.2 g/cc. Liquid-2: height h2 = 15.2 cm, density d2 = 13.6 g/cc. Liquid-3: height h3 = 15.2 cm, density d3 = 6.8 g/cc. What is the pressure exerted by the trapped NH3 gas?
- 0.4 atm
- 0.5 atm
Correct answer: 0.4 atm
Solution
Each liquid column exerts a pressure proportional to h*d. Converting to atm using mercury equivalent (76 cm Hg = 1 atm, density of Hg = 13.6 g/cc): P_liquid = h*d/(76*13.6). Summing all three columns and subtracting from 1 atm gives the gas pressure.
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