The total pressure in a flask containing air and ethanol at 257C is 878 mm Hg. If the pressure of the air in the flask is 762 mm Hg, the vapor pressure of ethanol is mm Hg.
To find the vapor pressure of ethanol, we need to subtract the pressure of air in the flask from the total pressure.
Vapor pressure of ethanol = Total pressure - Pressure of air
Let's substitute the given values:
Vapor pressure of ethanol = 878 mm Hg - 762 mm Hg
Now we can calculate this:
Vapor pressure of ethanol = 116 mm Hg
Therefore, the vapor pressure of ethanol in the flask is 116 mm Hg.