# Pressure and gas laws problems

1. A sample of nitrogen gas is connected to a manometer. Atmospheric pressure is 722 torr. The mercury column is at 355 mm in closed end and 156 mm in the open end. What is the pressure of the nitrogen in the bulb?

2. What is P gas if the barometric pressure is 750 mmHg and the mercury levels in the manometer is 9.5 mmHg depressed on the gas end?

3. What pressure is needed to compress 455 mL of oxygen gas at 2.50 atm to a volume of 282 mL?

4. The volume of an oxygen cylinder used as a portable breathing supply is 2.025 L. When the cylinder is at 29.2 ºC, it has a pressure of 723 torr. How many moles of oxygen gas are there? What is the mass of oxygen?

5. A sample of nitrogen gas has a volume of 1.75 L at STP. How many moles of nitrogen are present?

6.We have two containers of the same size; one is filled up with N2 and the other with CO2 at the room temperature and 1atm pressure.

a.What can you predict about the number of moles of N2 and CO2? Same, or different, or cannot predict. Circle your choice.

b.Which law is used here to make this prediction? ____________

c.Will the two cylinders weigh the same? If not, which cylinder will be heavier? ____________

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1. A sample of nitrogen gas is connected to a manometer. Atmospheric pressure is 722 torr. The mercury column is at 355 mm in closed end and 156 mm in the open end. What is the pressure of the nitrogen in the bulb?

1 atm = 760 torr = 760 mmHg

pressure of the nitrogen + (355-156) = 722

pressure of the nitrogen = 523 mmHg

2. What is P gas if the barometric pressure is 750 mmHg and the mercury levels in the manometer is 9.5 mmHg depressed on the gas end?

= 750 + 9.5 = 759.5 mmHg

3. What pressure is needed to compress 455 mL of oxygen gas at 2.50 atm to a volume of 282 mL?

P₁V₁ = P₂V₂

(2.5)(455) = P₂(282)

P₂ = 4.03 atm

4. The volume of an oxygen cylinder used as a portable breathing supply is 2.025 L. When the cylinder is at 29.2 ºC, it has a pressure of 723 torr. How many moles of oxygen gas are there? What is the mass of oxygen?

PV = nRT

(723/760)(2.025) = n(0.08206)(273+29.2)

n = 0.0777 mole

5. A sample of nitrogen gas has a volume of 1.75 L at STP. How many moles of nitrogen are present?

Molar volume at STP = 22.4 dm³

1.75/22.4 = 0.0781 mole

6.We have two containers of the same size; one is filled up with N2 and the other with CO2 at the room temperature and 1atm pressure.

a.What can you predict about the number of moles of N2 and CO2? Same, or different, or cannot predict. Circle your choice.

b.Which law is used here to make this prediction? _Avogadro's law

c.Will the two cylinders weigh the same? If not, which cylinder will be heavier? ___CO₂_________