Question

Picture of 2010 Todd Abronowitz Gas Laws problems, super fun if you’re in AP chem. Can you help a pre-AP struggling student out please?

Answer 1

Answer:

1. 0.422 atmospheres

2. 633281.25 Pascals

3. (a) Move up

(b) 868 mmHg

4. 868 mmHg

5. 775 mmHg

6. Partial pressure of He is 0.64 atm.

Partial pressure of oxygen is 1.29 atm.

Partial pressure of N is 2.57 atm.

7. 445.72 torr.

Explanation:

1. To convert 321  torr to atmospheres

1  atmosphere = 760 torr

∴ 1 torr = 1/760 atmospheres

Hence, 321 torr = 321 × 1/760 = 321/760 atmospheres = 0.422 atmospheres

2. To convert 6.25 atmospheres to Pascals, we have;

1 atmosphere = 101325 Pascals

∴ 6.25 atmospheres = 6.25 × 101325 Pascals = 633281.25 Pascals

3. (a) Here we have, given that the value of the pressure on the bottle = 830 mmHg, when the valve is opened, the mercury in the open-end arm will move up because the pressure of the gas inside the flask is more than the pressure on the other side of the open-end arm

(b) After the mercury stops moving the difference between the two columns will be the difference between the two pressures, that is 830 mmHg - 745 mmHg = 85 mmHg

4. From the diagram, it is seen that the differenc beteen the two columns is 123 mm, therefore, the pressure in the flask is 123 mmHg more than the external pressure, hence the pressure of the as in the flask = 745 mmHg + 123 mmHg = 868 mmHg

5. Here we have that the height of the mercury in the open-end is less than the height of the mercury on the arm closer to the flask, therefore, the pressure of the gas in the flask = 825 mmHg - 50 mmHg = 775 mmHg

6. Number of moles of He = 1 mole

Number of moles of oxygen, O = 2 mole

Number of moles of nitrogen, N = 4 mole

From Dalton's law of partial pressure we have that, the total pressure of a given mass of gas is equal to the partial pressure of the individual gases

$That \ is \ \chi _i = \frac{n_i}{n_{total}} \ and \ P_i = \chi_i \cdot P_{total}$

Hence;

Total number of moles = 1 + 2 + 4 = 7 moles

Mole fraction of He = 1/7

Partial pressure of He = 1/7×4.5 = 0.64 atm.

Mole fraction of oxygen, O = 2/7

Partial pressure of oxygen= 2/7×4.5 = 1.29 atm.

Mole fraction of N = 4/7

Partial pressure of N = 4/7×4.5 = 2.57 atm.

7. From Boyle's law

P₁×V₁ = P₂×V₂

Hence;

P₂ = P₁×V₁/V₂

Where:

P₁ = Initial pressure = 2.57 atm

V₁ = Initial volume =1.57 liters

V₂ = New volume = 6.88 liters

P₂ = New pressure = 2.57×1.57/6.88  = 0.59 atm.

To convert 0.59 atm. to torr, we multiply by 760 thus;

0.59 atm. = 0.59 × 760 torr = 445.72 torr.