# FInd the height of the column water when densities of mercury and water given

How high must a column of water be to exert a pressure equal to that of a 760.-mm column of mercury? (The density of water is 1.00 g/mL, whereas that of mercury is 13.6 g/mL.)

I understand the concept of barmeter but here they are talking about water column which is confusing me.How to corelate that with the densities given,please advice.

thanks

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Since Hg is 13.6 times as "heavy" as water, the equivalent height of the column can be calculated using a proportion:

1 mm H2O / 13.6 mm Hg = x mm H2O / 760 mm Hg

When we solve the proportion we find

x mm H2O = 1 mm H2O / 13.6 mm Hg x 760 mm Hg

If we wanted to generalize this to other substances (as you do in your next question)

height of substance A = density of substance A / density of substance B x height of substance B

spock

Tue, 2012-08-07 07:17

Ok, can. U explain how u are relating the height of column with density.The concept behind this relation has anything related to manometer or barometer or not ?

Please explain

mychemistry

Tue, 2012-08-07 13:49

Here is a picture of a eudiometer (which functions pretty much in the same manner as a barometer).

The pressure of the air in the open arm is balanced by the pressure created by the Hg in the closed arm.

The pressure of the Hg depends only on the height of the Hg column and the density (how heavy) the liquid is. You might want to think about a scuba diver to help you understand this. The deeper the diver goes (the taller the column of water pressing down on him), the higher the pressure exerted on him.

spock

Tue, 2012-08-07 19:10

Thank you but I am getting wrong answer, the answer that I got is 55.8 mm but the correct Answer is 10.3 meters

mychemistry

Wed, 2012-08-08 16:49

I'm sorry I reversed the numbers when I set up the ratio. I was correct when I said:

"

Since Hg is 13.6 times as "heavy" as water, the equivalent height of the column can be calculated using a proportion:"But the equation should have been

13.6 mm H2O / 1 mm Hg = x mm H2O / 760 mm HgWhen you solve this for x you get

x = 13.6 mm H2O/ 1 mm Hg x 760 mm Hg

x = 10,336 mm = 10.336 meters.

Sorry for the confusion.

spock

Wed, 2012-08-08 23:16