Homework Help: Chemistry

Posted by Bill on Wednesday, October 17, 2012 at 10:28pm.

A 0.528 gram sample of a metal, M, reacts completely with sulfuric acid according to: M+H2SO4 -> MSO4+H2

A volume of 205 mL of hydrogen is collected over water; the water level in the collecting vessel is the same as the outside level. Atmospheric pressure is 756.0 Torr and the temperature is 25°C. Calculate the atomic mass of the metal.

? g/mol

Is the answer 3.24x10^-3 g/mol?

Chemistry - DrBob222, Wednesday, October 17, 2012 at 10:40pm
No. If you will show your work I will look for the error. I think I answered this for you yesterday. I used as pressure of Ptotal = 756 mm + pH2O
and a table gave 23.8 mm for vapor pressure of H2O at 25C.
Chemistry - Bill, Wednesday, October 17, 2012 at 10:50pm
n=.0833 mols
molar mass=(.0833mols/.528g)=.158g/mol
Chemistry - DrBob222, Wednesday, October 17, 2012 at 10:54pm
What did you substitute for PV = nRT?
Chemistry - Bill, Wednesday, October 17, 2012 at 10:56pm
P=.995atm
V=.205L
n=?
R=.0821 Lxatm/molxk)
T=298K
Chemistry - Bill, Wednesday, October 17, 2012 at 11:08pm
It is 65.4g/mol
Chemistry - DrBob222, Wednesday, October 17, 2012 at 11:14pm
I would use P = (756-23.8)/760 = 0.963 atm; however, going with your number will still get close to the right answer.
PV = nRT or
n = PV/RT = 0.995*0.205/0.8206*298
n = 0.00834. You had to use some other (incorrect) version of n = PV/RT.
Then n = grams/molar mass or
molar mass = grams/n
molar mass = 0.528.0.00834 = ?
If you use P = (756-23.8)/760 I think you will get 65.4 which is Zn.

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