I got confused with calculating the molar mass

Question

Trial#	Mass of Mg (g)	Vol of H2 (mL)	Barometric Pressure (mmHg)	Temperature	Calculated Molar Mass of Mg
1	0.0354	36.2	745.9	21.0
2	0.0340	34.0	746.3	21.0
3	0.0352	35.8	755.5	20.5

Answer 1

First you will have to find the number of moles using the Ideal Gas Law equation: PV = nRT. The gas constant I will be using has units of L atm/ mol K. Therefore, the above units have to converted as follows:

P = 745.9 mmHg x 1 atm/ 760 mmHg = 0.9814 atm

V = 36.2 mL x 1 L/1000mL = 0.0362 L

n= ?

R = 0.0821 L atm/mol K

T = 21.0 C + 273 = 294 K (Based on my experience, I am assuming the Temperature is

given in Celsius)

Solve for n:

n = PV/RT = 0.9814 atm(0.0362 L) / 0.0821 L atm/mol K( 294 K) = 0.00147 mole

To find Molar Mass, you divide the mass by the moles:

MM = 0.0354g / 0.00147 mole = 24.08 g/mol

You will follow this same procedure for the remaining trials. Let me know if you have any problems.