# When a gas is collected in an upturned graduated cylinder in water, to what will the pressure in the cylinder when the measurement is taken is equal?

## $a . \text{the pressure of the gas PLUS}$ ${P}_{\text{saturated vapour pressure}} .$ $b . \text{the pressure of the gas LESS}$ ${P}_{\text{saturated vapour pressure}} .$ $c . \text{the pressure of the gas} .$ $d . \text{there is no relationship} .$

Feb 11, 2017

Well, $\text{option a..........}$

#### Explanation:

The given picture is the standard experimental setup.

Clearly, the gas expands against atmospheric pressure. When the level of water in the graduated cylinder is equal to the level of water in the reservoir, the PRESSURE of the gas in the CYLINDER is equal to the ambient pressure LESS the $\text{saturated vapour pressure of}$ $\text{water}$.

I again stress the level of water in the cylinder must match the level of water in the reservoir so that:

${P}_{\text{ambient"=P_"graduated cylinder"+ P_"saturated vapour pressure}}$

${P}_{\text{SVP}}$ is a constant that varies with temperature.

(sorry for all the SHOUTING! but I want to emphasize the approach.)