alleryStart learning →A closed-end mercury manometer shows a difference in levels of 26.4 cm. What is the gas pressure in pascals?
A3.52 x 10^4 Pa
B2.64 x 10^4 Pa
C3.52 x 10^3 Pa
D2.64 x 10^5 Pa
Answer & Solution
Correct answer: A. 3.52 x 10^4 Pa
1. In a closed-end manometer the gas pressure equals the full mercury height, with no atmospheric term to add.
2. Convert centimetres to millimetres: 26.4 cm x 10 mm/cm = 264 mm Hg.
3. Use 1 mm Hg = 1 torr, so the pressure is 264 torr.
4. Convert torr to atmospheres: 264 / 760 = 0.3474 atm.
5. Convert atmospheres to pascals using 1 atm = 101,325 Pa: 0.3474 x 101,325 = 35,200 Pa.
6. Written in standard form that is 3.52 x 10^4 Pa.
7. The option 2.64 x 10^4 Pa is the torr figure with a pascal label stuck on it, which is the trap.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 9 "Gases", section 9.1 Gas Pressure_
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