Question

Why cannot we use water instead of mercury in barometer?

Answer 1

In a barometer mercury is used to balance the atmospheric pressure with the mercury column in the tube and thus take the reading for pressure by letting out excess mercury. Now atmospheric pressure is very large thus a considerable weight of liquid is necessary to balance and take the reading. 

Now since mercury is dense (around 14 times than that of water) it needs only 1 meter tube to accommodate for the air pressure. Say instead water be taken in place of mercury then it would need a tube of 14 meters to balance atmospheric pressure and let out excess water, this tube would be too large to keep in a laboratory. 

Thank you

Answer 2

mercury has relative denser than water

mercury has low vapour pressure

mercury has low freezing point

mercury is a metal so it shines brightly which is easy to mark readings

meecury does not evaporate easily

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