The way the problem is stated makes it appear there is a lot of information that isn't used. Most of these problems want to know the pressure of the dry H2 gas at STP; however, this one just asks for pressure of dry H2 gas so I assume that is pressure at 25 C but dry gas instead of wet. That simplifies the problem quite a bit.
Ptotal = pH2 dry + pH2O
754 mm Hg = pH2 + pH2O.
Look up pH2O in your text/notes. It is a function of T and it will be called "vapor pressure" tables or vapor pressure H2O. I don't have these tables memorized but at 26 C the vapor pressure of H2O will be approx 25 mm.
Substitute that into the formula above and solve for pH2. That will be the pressure of dry H2 at 26 C. The problem asks for P in atm so convert. P in atm = P in mm/760 = ?
472 mL of H2 was collected over water when 1.256g Zn reacted with excess HCl. The atmospheric pressure during the experiment was 754 mmHg and the temp was 26C. What is the pressure in atm of the dry hydrogen gas in the mixture.
I don't know how to answer this.
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