Quiz 4 1 A sample of gas has an initial volume of 40 L at a

Quiz 4 1. A sample of gas has an initial volume of 40 L at a pressure of 730 torr, what will be the volume of the gas when the pressure decreases to 560 torr? 2. What is the pressure of 6.2 g hydrogen in a 35 L container at 25°C? 3. 4 g of a gas sample takes up volume of 44.8 L at STP. If the gas identity is that of a diatomic molecule, what would you suspect the gas to be? 4. If a certain reaction produced 5.67 g of O2 that was collected into a balloon, what would the expected volume of the balloon be at 23°C and 0.894 atm? 5. An isolated bacterial culture produced 51.5 mL of methane, CH, at 33 C and 752 mmHg. What is the volume of this methane at standard temperature and pressure (STP)?

Solution

1. initial                              final
   V1 = 40L                            V2 =
   P1 = 730 torr                       P2 = 560 torr
             P1V1 = P2V2
               V2 = P1V1/P2
                    = 730*40/560   = 52.14L
2. no of moles of H2(n) = W/G.M.Wt
                      = 6.2/2 = 3.1moles
T = 25+273 = 298K
V = 35L

PV = nRT
P   = nRT/V
      = 3.1*0.0821*298/35   = 2.16atm
3.22.4 L of gas = 1 mole
44.8 L of gas = 1mole*44.8/22.4 = 2 moles
molar mass of gas = 4/2 = 2 g/mole
that diatomic gas is H2
4. no of moles of O2(n) = W/G.M.Wt
                          = 5.67/32   = 0.18 moles
P = 0.894atm
T = 23+273 = 296K
PV = nRT
V   = nRT/P
    = 0.18*0.0821*296/0.894   = 4.9L

5. experimetal conditions                           STP conditions
   V1 = 51.5ml                                      V2 =
   P1 = 752mmHg                                     P2 = 760mmHg
   T1   = 33+273 = 306K                             T2 = 273K
                 P1V1/T1   = P2V2/T2
                      V2   = P1V1T2/T1P2
                           = 752*51.5*273/306*760
                            = 45.46ml