posted by amy .
The following reaction is carried out as a source of hydrogen gas in the laboratory:
Zn(s) + 2HCl(aq) ---> ZnCl2(aq) + H2(g)
If 305 mL of hydrogen gas is collected over water at 25 °C at a total pressure of 746 mm Hg , how many grams of Zn reacted?
Use PV = nRT to solve for n = number of moles H2 gas. Remember V is in liters, p in atmospheres, and T in Kelvin. You will need to look up the vapor pressure of water at 25 C and calculate pressure as follows:
(746 mm - mm vapor pressure @ 25C)/760.
Using the coefficients in the balanced equation, convert moles H2 to mols Zn.
Finally, convert moles Zn to grams. g = moles x molar mass.