Ji Zhang
12/12/1998
Period 1 Chem
Lab: Molar Volume of a Gas

Objectives:
	The objectives of this lab are to determine an experimental molar volume for hydrogen; to study 
mass-volume relationships in chemical reactions; and to become familiar with the relationship between the 
density and molecular mass of a gas.

Data:






1
length of Mg ribbon


4.00cm
2
mass of 1 cm Mg ribbon


.0116g
3
mass of Mg ribbon used


.0464g
4
moles of Mg ribbon used


.00191m
5
volume of H gas collected


46mL
6
temp. of water and of gas


25C
7
barometric pressure


775mm
8
vapor pressure of water


23.8mm
*9
pressure of dry hydrogen gas


751.2mm
*10
volume in liters of hydrogen gas 


41.65mL

(corrected to STP)



11
moles of hydrogen gas (equal


.00191m

to moles of Mg)



12
molar volume (liters/1mole)


21806  l/m
13
theoretical molar volume for 


22400  l/m

perfect gas



14
percentage deviation of exp.


97.35%

and theo. Value








calculation
s




*9
barometric pressure- vapor pressure of H2O= 
pressure of dry hydrogen gas




775mm - 23.8mm= 751.2mm








*10
PV/T = PV/T









751.2t*45mL

760t * 
XmL


----------------  =

--------------
--


298K

273K (this is STP)







X= 41.65mL (by cross multiplication)




Sketch of experiment: please see next page

Conclusion question: sources of error
  There were various possible sources of error in this experiment.  If air was let in the gas tube during or 
before the magnesium reaction, then the volume of the gas inside the tube will be too big.  If the 
magnesium did not completely react with the hydrochloric acid, then not enough gas will be produced and 
the volume of the gas produced will be too small.  Magnesium may not react completely due to various 
reasons.  For example, it may not be 100% pure.