Question

a mercury manometer is used to measure the pressure of a confined sample of gas in a bulb, as shown in the figure below. atmospheric pressure is 747 torr and the temperature is 25°c.
if this is a closed - end manometer and h = 11.3 cm, what is the pressure of the gas in the bulb (in torr)?
torr
if this is an open - end manometer and h = 11.3 cm, what is the pressure of the gas in the bulb (in torr)?
torr

Explanation:

Step1: Closed - end manometer pressure calculation

For a closed - end manometer, the pressure of the gas \(P_{gas}\) is equal to the pressure difference indicated by the mercury column. Since \(h = 11.3\ cm=113\ mm\) (because \(1\ cm = 10\ mm\)), and pressure in terms of mercury column height (in mm) is equivalent to torr (since \(1\ mm\ Hg=1\ torr\)).
\(P_{gas}=h\)

Step2: Open - end manometer pressure calculation

For an open - end manometer, the pressure of the gas \(P_{gas}\) is related to the atmospheric pressure \(P_{atm}\) and the height of the mercury column. If the gas pressure is higher (as the mercury is pushed towards the open end), \(P_{gas}=P_{atm}+h\). Given \(P_{atm} = 747\ torr\) and \(h = 113\ torr\) (since \(h = 11.3\ cm = 113\ mm\) and \(1\ mm\ Hg = 1\ torr\))
\(P_{gas}=747 + 113\)

Answer:

113 torr
860 torr