Video Transcript
A torr is a unit that is defined as being equal to the pressure produced by one millimeter of mercury. What is the pascal-to-torr ratio? Give your answer to the nearest integer.
When we talk about one millimeter of mercury, we can think of an apparatus used to measure pressure. The way it works, mercury in the apparatus is exposed to the atmosphere. This pressure is counterbalanced by the weight of a column of mercury that’s inside a part of the apparatus shielded from the atmosphere. If the mercury in this column were to change its height by one millimeter, that will correspond to some change in atmospheric pressure.
It’s common to measure atmospheric pressure in units called pascals. What developed then is a correspondence between this unit of pressure and millimeters of mercury. Here, Hg is the atomic symbol for mercury. A change of one millimeter in the height of the mercury column is approximately equal to 133.3 pascals. This way, if we witnessed such a change in the height of the mercury column of our apparatus, we would be able to translate that change into a change in pressure in pascals.
Our question statement tells us about another unit of pressure called the torr. We’re told that one torr is defined as the pressure produced by one millimeter of mercury. Here then, we’re letting a certain height of mercury in a column correspond to a certain pressure. We saw a moment ago that this height of mercury corresponds to a certain number of pascals. If 133.3 pascals of pressure are equivalent to a change in height of the mercury column of one millimeter and that same change in the height of the column is equal to one torr, then 133.3 pascals equals one torr.
Our question asks us to give our answer to the nearest integer. 133.3 rounds to 133. And so to the nearest integer, 133 pascals is one torr. This is the pascal-to-torr ratio.
