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# CHEMISTRY HELP!!!!!!!!!!!!!!?

What is the pressure of dry carbon dioxide gas if it was collected over water at 28°C and had a total pressure of 45.7 kPa?

please explain what your doing step by step i really dont get this and dumb it down a bit i got a test tomorrow

also my study guide says that you may need to refer to vapor pressure table for water for some problems.... idk if you need it for this prob or not. tell me if you used it please

and can you tell me the formula for this? i know its something like ptotal=......

### 1 Answer

- BrendaLv 47 years agoFavorite Answer
The total pressure = the sum of the two pressures you have, that of the CO2 and that of the water vapor that gets into it when it is collected "over water." The CO2 was bubbled into a tube of water, pushing the water out as the gas entered, but some evaporated water stays in the CO2)

so YES - you need to look up the partial pressure of that water vapor on your table (at 28 degrees.)

Subtract that value from the total pressure to get the pressure of just the "dry" CO2

Here's the official equation to use: Dalton's Law of Partial Pressures

P (total) = P (CO2) + P (water at 28 C)

Good luck on your test tomorrow.

Source(s): retired Chemistry teacher