High School

8. A solution contains a mixture of two volatile substances, A and B.

The mole fraction of substance A is 0.35. At 32°C, the vapor pressure of pure A is 87 mmHg, and the vapor pressure of pure B is 122 mmHg. What is the total vapor pressure of the solution at this temperature?

a) 110 mmHg
b) 209 mmHg
c) 99.3 mmHg
d) 73.2 mmHg

Answer :

The total vapor pressure of the solution is (c) 99.3 mmHg.

What is temperature?

A substance's or an object's temperature is a measurement of how hot or cold it is. It is a characteristic of matter that has to do with the typical kinetic energy of the atoms or molecules that make up the thing or material. Normally, temperatures are expressed in either degrees Celsius (°C) or degrees Fahrenheit (°F).

How do you determine it?

Raoult's law, because substance A's mole fraction is 0.35, it follows that substance B's mole fraction must be 0.65. (since the two mole fractions must add up to 1). The partial pressures of A and B in the solution can be determined using Raoult's law:

A's partial pressure is calculated as 0.35 x 87 mmHg, or 30.45 mmHg.

B's partial pressure is equal to 79.3 mmHg (0.65 x 122 mmHg).

The partial pressures of A and B are added to determine the solution's overall vapor pressure:

Total vapor pressure equals partial pressures of A and B, or 30.45 mmHg, 79.3 mmHg, and 109.75 mmHg respectively.

Rounding to the nearest tenth, we obtain 109.8 mmHg, which is the value that is most similar to option (c) 99.3 mmHg. Hence, the correct response is (c) 99.3 mmHg.

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The total vapor pressure of the solution at 32°C with a mole fraction of substance A at 0.35 is approximately 110 mmHg, calculated using Raoult's Law.

To calculate the total vapor pressure of the solution at 32°C with a mixture of two volatile substances A and B, where the mole fraction of substance A is 0.35, and the vapor pressures of pure A and B are 87 mmHg and 122 mmHg respectively, we use Raoult's Law:

Total vapor pressure (Ptotal) = (mole fraction of A × vapor pressure of A) + (mole fraction of B × vapor pressure of B)

Since the mole fraction of B is 1 - 0.35 = 0.65, the calculation is as follows:

(0.35 × 87 mmHg) + (0.65 × 122 mmHg)

(30.45 mmHg) + (79.3 mmHg)

109.75 mmHg

The correct answer is approximately 110 mmHg, which corresponds to option a).