## Multiple Choice and Short Answer

Problem One
What pressure is necessary to increase the volume of 1.0 L of a gas at a pressure of 450 torr to a solume of 10 L?

Incorrect
Volume and pressure are inversely proportional. If the pressure increases, the volume decreases.

Correct
(450 torr x 1.0 L) / 10 L = 45 torr

Incorrect
This is the standard pressure but has no bearing on the problem.

Problem Two
A 1.0 L sample of a gas is at a pressure of 2 atmospheres. What volume will the sample have at a pressure of 1 atmosphere?

Incorrect
Volume and pressure are inversely proportional. If the pressure decreases, the volume increases.

Incorrect
Volume and pressure are inversely proportional. If the pressure decreases, the volume increases.

Correct
1.0 L x (2 atm/ 1atm) = 2.0 L

Problem Three
A 1.0 L sample of a gas is at a temperature of 273 K. What will the volume be if the temperature is increased to 546 K?

Incorrect
Volume is directly proportional to absolute temperature. If the temperature doubles, the volume doubles.

Incorrect
Volume is directly proportional to absolute temperature. If the temperature doubles, the volume doubles.

Correct
1.0 L x (546 K/ 273 K) = 2.0 L

Problem Four
A 1.0 L sample of a gas is at a temperature of 25 °C and a pressure of 670 torr. If the volume is kept constant and the temperature is increased to 50 °C, what will the new pressure be?

Incorrect
Pressure is directly proportional to absolute temperature (the absolute temperature has increased by a factor of 323 K/298 K.)

Incorrect
Pressure is directly proportional to absolute temperature (the absolute temperature has increased by a factor of 323 K/298 K.)

Correct
670 torr x (323 K / 298 K) = 726 torr

Problem Five
A 1.0 L sample of a gas is at a temperature of 100 K and a pressure of 1.0 atm. If the temperature is increased to 200 K and the pressure is increased to 2.0 atm, what will the new volume be?

Incorrect
Because the absolute temperature doubles and the pressure doubles, the volume remains the same.

Correct
Because the absolute temperature doubles and the pressure doubles, the volume remains the same.

Incorrect
Because the absolute temperature doubles and the pressure doubles, the volume remains the same.

Problem Six
A 1.0 L sample of a gas is at a temperature of 100 K and a pressure of 0.50 atm. When the conditions are changed to STP, what is the new volume?

Correct
1.0 L x (273 K/100 K) x (0.50 atm/1.0 atm) = 1.4 L

Incorrect
This accounts only for the change in temperature.

Incorrect
This accounts only for the change in temperature.

Problem Seven
A 1.0 L sample of a gas is at a temperature of 25 °C and a pressure of 670 torr. How many moles of the gas are present?

Correct
n = PV/RT = (670 torr/760 torr)(1.00 L) / (0.0821 L-atm/K-mole)(298 K) = 0.036 moles

Incorrect

Incorrect

Problem Eight
A 2.8 g sample of N2 occupies a volume of 2.2 L at 0.0 °C. What is the pressure of the sample?

Incorrect
2.8 g is 2.8 g 28 g/mole = 0.10 mole, which at STP occupies 2.2 L.

Correct
2.8 g is 2.8 g 28 g/mole = 0.10 mole, which at STP occupies 2.2 L.

Incorrect
2.8 g is 2.8 g 28 g/mole = 0.10 mole, which at STP occupies 2.2 L.

Problem Nine
A 2.8 g sample of a compound occupies a volume of 2.2 L at 0.0 °C and 1.0 atm. What is the molecular weight of the compound?

Correct
At STP 2.2 L is 2.2 L 22.4 L/mole = 0.10 mole. If 2.8 g is 0.10 mole, what is the mass of 1.0 mole?

Incorrect
At STP 2.2 L is 2.2 L 22.4 L/mole = 0.10 mole. If 2.8 g is 0.10 mole, what is the mass of 1.0 mole?

Incorrect
At STP 2.2 L is 2.2 L 22.4 L/mole = 0.10 mole. If 2.8 g is 0.10 mole, what is the mass of 1.0 mole?

Problem Ten
A 0.10 g sample of N2 is present with 0.20 mole of O2. The total pressure of the mixture is 1.0 atm. What is the partial pressure of O2?

Incorrect
The number of moles of O2 is two-thirds of the total number of moles. Thus, it exerts two-thirds of the total pressure.

Incorrect
The number of moles of O2 is two-thirds of the total number of moles. Thus, it exerts two-thirds of the total pressure.

Correct
The number of moles of O2 is two-thirds of the total number of moles. Thus, it exerts two-thirds of the total pressure.

Problem Eleven
A sample of carbon dioxide has a volume of 200 mL at -10 °C and a pressure of 670 torr. What volume will the sample have at -10 °C and 230 torr?

583 mL

Problem Twelve
A sample of carbon dioxide has a volume of 200 mL at -10 °C and a pressure of 670 torr. What volume will the sample have at 50 °C and 670 torr?

246 mL

Problem Thirteen
A sample of carbon dioxide has a volume of 200 mL at -10 °C and a pressure of 670 torr. What volume will the sample have at 50 °C and 230 torr?

715 mL

Problem Fourteen
A sample of carbon dioxide has a volume of 200 mL at -10 °C and a pressure of 670 torr. How many grams of carbon dioxide are present in the sample?

0.36 g

Problem Fifteen
What is the density of carbon dioxide at STP?

1.96 g/L

Problem Sixteen
What is the density of carbon dioxide at 500 torr and 50 °C?

1.09 g/L

Problem Seventeen
What volume of carbon dioxide will contain 6 x 1022 molecules at 500 torr and 50 °C?

4.0 L

Problem Eighteen
A sample of N2 occupies 500 mL at 25 °C and 350 torr. What pressure is required at a temperature of 100 °C to achieve a volume of 1000 mL?

219 torr

Problem Nineteen
A 1.0 g sample of ethane (C2H6) occupies 1.0 L at a temperature of 25 °C. What is the pressure of the gas?

0.81 atm

Problem Twenty
A gas has a density of 1.67 g/L at 35 °C and 700 torr. What is the molecular weight of the gas.

46 g/mole

Problem Twenty One
A 0.450 g sample of a gas occupies 2.05 L at 0.0 °C and 0.5 atmospheres. What is the molecular weight of the gas?

10 g/mole

Problem Twenty Two
The composition of air is approximately 21% oxygen, 78% nitrogen, and 1% argon. If the total pressure is 1.0 atmosphere, what is the partial pressure of argon?

0.01 atm

Problem Twenty Three
If 1.6 g of methane (CH4) at a pressure of 600 torr is collected over water at 25 °C, what volume is collected? [The vapor pressure of water at 25 °C is 25 torr.]