Question

If an ideal gas sample at 534 torr pressure occupies 345 mL at 25°C, how many moles of that gas are present? Report your answer to 3 significant figures.

If If an ideal gas occupies 736 mL at 45°C and 719 torr, what volume will it occupy at 105°C and 972 torr? Report your answer in mL to 3 significant figures.

A 2.43 g sample of a gaseous compound has a pressure of 496 torr in a volume of 250 mL at 37°C. What is its molar mass? Report your answer to 3 significant figures

Answer 1

1.

PV = nRT

P   = 534 torr   = 534/760   = 0.7 atm

V   = 345ml   = 0.345L

T   = 25+273 = 298K

PV   = nRT

n     = PV/RT

       = 0.7*0.345/0.0821*298    = 0.00987moles

2.

Initial                                                                                          Final

V1   = 736ml                                                                            V2 =

T1   = 45+273 = 318K                                                            T2 = 105+273   = 378K

P1   = 719 torr                                                                           P2 = 972 torr

              P1V1/T1     =         P2V2/T2

                      V2       = P1V1T2/T1P2

                                 = 719*736*378/318*972   = 647.15ml >>>>answer

3. PV = nRT

     n    = W/M

PV   = WRT/M

M    = WRT/PV

P   = 496torr = 496/760   = 0.652atm

V    = 250ml   = 0.25L

T = 37+273    = 310K

W   = 2.43g

M    = WRT/PV

       = 2.43*0.0821*310/0.652*0.25   = 379g/mole