posted by K .
A 0.0677g sample of magnesium metal reacted with excess hydrochloric acid to produce 69.9 ml of hydrogen gas. The gas was collected over water at 21.0 degrees Celsius. The levels of water inside and outside the gas collecting tube is identical. The water vapor pressure at 21.0 degree Celsius is 18.6 mmHg and the atmospheric pressure is 755 mmHg. Calculate the experimenal molar volume of hydrogen gas at STP. Write a balanced chemical equation for the reaction.
Mn + 2HCl ==> MnCl2 + H2
g Mn = 0.0677
moles Mn = 0.0677/54.94 = ?? = n
P = (755-18.6)/760 = ??atm
T = 21 + 273 = ??K
Use PV = nRT and substitute the above numbers. Solve for V (in liters). This will be the volume in liters for n moles you calculated above. Then Volume from above/n from above will give you the volume (in liters) for 1 mole which, by definition, is the molar volume. If this is an experiment you conducted, the answer is close to the accepted value.